Tube Talk
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Gold Member Username: My_rantzAustralia Post Number: 2008 Registered: Nov-05 | Ever try to play Santana without distortion? It's an accurate part of reproduction of his guitar work as it is with many others back through the decades. But you know this - you stated so :-) But it's getting that faithfull reproduction - that ain't easy! Nor is an unfaithfull reproduction!!!! |
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Gold Member Username: John_aLondonU.K. Post Number: 4813 Registered: Dec-03 | Sorry I'm now a once-a-week poster. Nuck - we want the original distortion: nothing added; nothing taken away. Don't you agree? In the audio system itself, we want no distortion. Or, at least the closet approach to the original that we can get. Is that the answer.....?! Hi, MR! |
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Gold Member Username: Mike3Wylie, Tx USA Post Number: 1490 Registered: May-06 | Uh, John, that was two weeks... must be the time warp you are existing in. LOL! |
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Gold Member Username: John_aLondonU.K. Post Number: 4814 Registered: Dec-03 | The post of the week before was on another thread, Michael. Yes, I just checked - Oct 4. Well, 8 days, it's close.... https://www.ecoustics.com/electronics/forum/home-audio/21154.html I was reminded of the thread that Jan started called "Do you listen" where we all fought and argued. Seems to me it's the same question. If the original sound had distortion, then let's get a system that reveals all. Not one that gets carried away and adds some more of its own. Nuck.....? All opinions allowed, here. We've fought before, and all now accept that we are all, um, "Strange".....? I got into a discussion about recordings and background music some months ago with a female friend of a friend who kindly told me that my argument was "bonkers". I am not sure that translates. Best wishes! |
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Gold Member Username: John_aLondonU.K. Post Number: 4815 Registered: Dec-03 | Update to Sept 30, above. I obtained two JJ EL34s, one as replacement for the shot one, and one to keep as a spare. So I tried a complete and working set of 4 x EL34s on the PLPL Two and it sounded fine at moderate volumes, but distortion crept in too soon on peaks. So I replaced the 4 x EL34 with the original 4 x KT88 badged "Prima Luna". Distortion gone. Wonderful sound. KT88s go louder and that's about it. Any change in sound quality at same volume is below my threshold of awareness. With higher efficiency speakers than Quad ESL63, or ones less demanding of current, then I think one could save money and get the same result by replacing KT88 with EL34. Or buy a PLPL One in the first place. |
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Platinum Member Username: NuckPost Number: 11292 Registered: Dec-04 | John, the KT88's are going to play harder and hotter than the EL34's no doubt. Your amp has the plate voltage to run them, which is choice. I like the fuzzy 34 sound, and my Svetlana's are pretty good. I have heard different stuff about JJ tubes, so I may be wary. Good stuff John. |
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Gold Member Username: John_aLondonU.K. Post Number: 4817 Registered: Dec-03 | Thanks, Nuck. I maybe play music louder than some. I was just feeling immersed and happy when one of the folk next door knocked on the front door to ask me to turn it down. The man I spoke to in the JJ supplier probably had it right - the EL34 is the original Mullard design, and the KT 88 is similar but tweaked to give as much power as can be from the same basic set-up. So the glass bottles are bigger. But the sound quality is the same at normal levels. I said "aren't the EL34s supposed to be warmer?" and he said "If you think that then you're halfway to comparing to sound of cables.." or words to that effect. EL34: http://www.sequoia.co.uk/shop/product.php?p=145 KT88: http://www.sequoia.co.uk/shop/product.php?p=159 |
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Platinum Member Username: NuckPost Number: 11297 Registered: Dec-04 | They changeout in some amps, John, but not my little one, no transformer for the current, and thats the difference. If the output amps run out of gas, then the voltage on the plate drops in a hurry, thats a fuzzy edge for 34's in a guitar amp, but thats where some players want it to be, and I have enjoyed the little amp here with Apollo source and Ling FRSD speakers. If you can support the 88's, then I would likely play the same tubes. I love 88's and the Svetlana's, again, are hard to beat, but thats all I have heard lately. |
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Silver Member Username: Jazzman71Phoenix, AZ USA Post Number: 583 Registered: Dec-07 | Just replaced the EH KT88s in my Cary SLI-80 F1 integrated wtih SED "Winged C" 6550Cs due to a tube failure. The difference to me is striking to say the least. I will attempt to describe the main differences I hear, since they are now burned in for about 100 hours. The detail is much better. I notice that I can focus on any particular instrument, regardless of relative volume to other players, and essentially hear every note clearly. Percussion is incredible--every brush, cymbal, rim shot, block, etc is just right there in the room, from the quietest to the loudest. The ECM recordings I have and use as reference (ECM discs to me are second to none in recording quality), are just beautifully reproduced. I notice the sustain is improved. This may be related to above, and I'm not really sure how to define it, but I notice it more, especially in very quiet passages. More space around the instruments. Improved soundstage. More depth I think is probably the best way to describe it. Very noticeably improved wrt just about every measure I can think of. And mind you this is with crappy Monster ICs and speaker cabling, which are obviously the next thing to go. I just have not decided on what cables to purchase, or whether to take a shot at making some. I am really looking forward to the improvements from better cabling. These tubes seem to run a bit hotter than the EH KT88s, but are supposed to be he!! for stout, so we'll see. Biased on the low end of the 75-100 mA range spec'd for my amp, they deliver plenty of sound. http://www.sed-usa.com/index.asp?strType=Content&strPage=6550C Very, very satisfied. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13420 Registered: May-04 | . Try running the bias up just a bit and listen for improvements. By choosing a hotter bias, the amp runs closer to a class A operation than a strict class AB. Increase the bias slowly listening for changes as you go. Do not over bias the tubes into cherry red plates. . |
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Platinum Member Username: NuckPost Number: 11880 Registered: Dec-04 | Neil, what plate voltage are you running? |
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Silver Member Username: Jazzman71Phoenix, AZ USA Post Number: 590 Registered: Dec-07 | Nuck, I think plate voltage is 450 assuming 117 VAC for the mains, but Cary manual leaves a lot to be desired. JV, if the tube sticker says 62 mA bias and the amp manual says bias to 75-100 mA, which do you go by? |
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Platinum Member Username: NuckPost Number: 11888 Registered: Dec-04 | Neil, go by the amp rating and go up from there.you might end up at 75 or more. Mind that the plate voltage remains stable as you bias up. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13423 Registered: May-04 | . Yes, use the amplifier's bias setting, unless you have been told by the tube manufacturer or retailer the tube should be run "no hotter than ... ". Since you're unsure about this, I think it would be best to call the retailer and ask their opinion. You are unlikely to damage either the tube or the amp by running the bias at the minimum recommended by Cary, but why risk anything when a call will answer the questions you have? . |
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Silver Member Username: Jazzman71Phoenix, AZ USA Post Number: 591 Registered: Dec-07 | Nuck, I've pretty much followed the amp bias range. What I failed to do with the last set was to readjust the bias beyond the initial few weeks. That undoubtedly cost me some tube life as the bias probably needed adjusting as the tubes aged. Will follow up with the tube folks to make sure, which should be easy as the tube guy sold me the amp as well. Thanks to you both. |
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Silver Member Username: HawkbillyNova Scotia Canada Post Number: 545 Registered: Jul-07 | How did you end up deciding on that tube Neil ? Sounds like a great choice. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13424 Registered: May-04 | . When adjusting bias keep in mind running the bias higher will result in the tube staying on just a bit longer and switching on a bit sooner in the push/pull cycle and result in a few extra watts. It will also decrease tube life, sometimes dramatically. Running the bias lower has the opposite effects. . |
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Silver Member Username: Jazzman71Phoenix, AZ USA Post Number: 596 Registered: Dec-07 | CH, I read some on-line threads by people running the same or similar amps, and the guy who sold me the amp recommended it. It's nearly three times the cost of the EH KT88s, but wow what a difference. JV, yes I'm generally aware of the bias impact on output and tube life. These tubes are supposedly tough, but I don't want to shell out another $200 in a couple of months for new ones. After checking following one of your previous posts, I learned that I should be shooting for 75-80 mA. I will be measuring it again a few days, and will see if it has drifted at all. I will also try pushing gradually up to 80 mA and see if I notice a difference. Thanks for the info. |
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Gold Member Username: ExerciseguyBrooklyn, NY United States Post Number: 2528 Registered: Oct-04 | Any opinions? This amp seems to pack a lot of goods into a nice tidy package. http://www.acoustic-dimension.com/pure%20sound/pure-sound-A30-integrated-amplifier.htm http://cgi.ebay.com/Bewitch-6550-KT88-Russian-Tube-Integrated-Amplifier Yeah, yeah, I know it's Chinese Gray-market, I don't think I'm buying, just looking.  |
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Platinum Member Username: NuckPost Number: 12114 Registered: Dec-04 | AUDIO Pradikat: überragend, 100 Punkte, High End Klasse, 5 Ohren. "Prachtvoll aufgebaut und bestückt, extrem feinsinniger, farbenreicher Klang" What more could I add? If there is warranty support, and the Alps and other parts are genuine, then this unit deserves a shot. |
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Gold Member Username: ArtkAlbany, Oregon USA Post Number: 9445 Registered: Feb-05 | If you're shopping for a tube amp Christopher Agon seems to always have a supply of reasonably priced ones. |
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Gold Member Username: ExerciseguyBrooklyn, NY United States Post Number: 2529 Registered: Oct-04 | How did you pick up your Yaqin? |
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Gold Member Username: ExerciseguyBrooklyn, NY United States Post Number: 2530 Registered: Oct-04 | Just looking Art, this seems like a reasonably good deal, if all holds true. The Pure Sound A30/Bewitched 6550 seem to be more widely available in the UK. |
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Gold Member Username: ArtkAlbany, Oregon USA Post Number: 9447 Registered: Feb-05 | Hey...I have "One Tube" now...back in bizness! |
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Gold Member Username: My_rantzAustralia Post Number: 2160 Registered: Nov-05 | These Bewitch valve amps are often on Ebay here in Aus Chris. I read on a forum here sometime back that the buyer was very happy with his purchase and that it was well worth the money. The Yaquin seem very good value also. |
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Silver Member Username: Jazzman71Phoenix, AZ USA Post Number: 662 Registered: Dec-07 | "If you're shopping for a tube amp Christopher Agon seems to always have a supply of reasonably priced ones." PrimaLuna leaps to mind. |
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Gold Member Username: ExerciseguyBrooklyn, NY United States Post Number: 2531 Registered: Oct-04 | Yeah there are plenty of options out there, this Pure Sound/Bewitched just seemed to jump off the page at me as a good deal. Buyers seemed to be pretty satisfied. |
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Silver Member Username: Jazzman71Phoenix, AZ USA Post Number: 667 Registered: Dec-07 | CM, I would check into the guts of the amp a little bit, as I did not find much info other than the glossy 1/2 page reviews. From what I saw, it seems like a good unit, but....caveat emptor. In that price range, I would look for soft start, point-to-point wiring, WBT, etc. That's why I sort of landed on the PrimaLuna. There's a Prologue One on A'gon for under a grand, and a recent one listed (SOLD) for $725. 35 wpc, EL34 output tubes, high quality build, seems like a fabulous amp for the money. No phono stage, but I don't believe the Bewitched has one either?? Just an opinion. Cheers. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13557 Registered: May-04 | . http://web.archive.org/web/20050306024649/www.netaxs.com/~vkalia/beginner.html |
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Gold Member Username: StryvnWisconsin Post Number: 1100 Registered: Dec-06 | Great link, Jan. Thanks |
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Platinum Member Username: NuckPost Number: 12528 Registered: Dec-04 | Anybody can roll tubes, can you roll the stuff inside??? http://www.dailymotion.com/video/x3wrzo_fabrication-dune-lampe-triode_tec |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13663 Registered: May-04 | . I kept waiting for him to make one of those little glass unicorns. |
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Platinum Member Username: NuckPost Number: 12535 Registered: Dec-04 | You didn't look for partez deux, he makes glass buttplugs. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13664 Registered: May-04 | . Any EMT will tell you a Coke bottle works just as well - till it forms a vacuum and gets stuck. . |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 2632 Registered: Feb-07 | "glass buttplugs"? That sounds like a recipe for disaster. Or at least a trip to the emergency room. |
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Gold Member Username: Mike3Wylie, Tx USA Post Number: 2012 Registered: May-06 | I just got one of my amps back from its return visit to the doc's office. I had a minor issue with not being able to run a 12AX7 for the splitter and had to us a 12AU7 in its slot temporarily. Then the other morning the amp developed a humming out of the right channel. Two caps the size of extra small Red Bull cans had to be replaced. Now all I have to ask is how many of you have a neighborhood McIntosh qualified repairman who carries these in original McIntosh stock? Nothing like keeping the amp original! Then he only charged me for the parts, no labor, as he did not like it that I had to have a return visit even though these passed his initial tests about a month ago. Peaks and slams abundant with Carlos Santana's guitars tonight! A 1960's MAC amp in like new condition is a beauty to hear and behold. Two of them, priceless! |
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Platinum Member Username: ArtkAlbany, Oregon USA Post Number: 10061 Registered: Feb-05 | Excellent Mike! We have a great Mac guy in Eugene, Oregon at the Stereo Workshop, Kevin. It appears your guy earned your respect. |
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Gold Member Username: My_rantzAustralia Post Number: 2262 Registered: Nov-05 | Yep, it's great to have a "do right by you" service guy. Good one Mike, enjoy those old fellas. |
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Platinum Member Username: NuckPost Number: 12731 Registered: Dec-04 | Thats a sweet repair, Mike! So you are again running the higher gain 12AX7 in both? |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13690 Registered: May-04 | . In the phase splitter position the tube has no relevant gain - it is run as a unity gain device (1 in = 1 out) and operates only to separate positive from negative waveforms and send them on their way to the appropriate circuits in a push-pull amplifier. You could run any 12 AX"?"/ECC83/5751 tube in this position but it's best to have both amps using the same tube brand and type since this tube is the first the signal passes through it does rather obviously affect the sound of the amp. . |
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Platinum Member Username: NuckPost Number: 12734 Registered: Dec-04 | Why would dry caps allow one tube type but not another? Or did I miss the coorelation? |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13691 Registered: May-04 | . I don't think this problem had anything to do with the tube. The issue with the tube was a problem that occurred before MW had the amp serviced if I remember right. This problem occurred with the filter caps and as I understand it had nothing in particular to do with the tube. The phase splitter is run as unity gain but if you put in a lower gain tube, you will not have true unity gain out. You can run any 12A"?" in that position but you won't necessarily get the same results if you run the wrong tube. The results will just not be as dramatic as if the wrong tube was used in a driver or pre amp stage. My guess would be this amp's caps failed because it had sat for some time - possibly a few years - and when it was brought back up to power by the seller to check for operation it was just plugged in and hit with 120VAC. I think that's the story on this one amp. The other amp MW has had already been worked on when he bought it. This amp didn't work when we first plugged it in at Mike's and Les replaced all the coupling caps but not the supply or filter caps. Is that right, Mike? . |
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Gold Member Username: Mike3Wylie, Tx USA Post Number: 2013 Registered: May-06 | Jan's description is spot on. While I am not getting a volume disparity with the 12AX7 back in place I heard enough of the 12AU7 that was substituting to say without a doubt, to my ears, there is more drive from the amp with the correct tube in the phase splitter socket. Certainly on the Kim Carnes LP I am currently spinning! |
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Platinum Member Username: NuckPost Number: 12742 Registered: Dec-04 | So the splitter was getting a little 'loose' due to drainage from the caps? Maybe? Running the same plate voltage for both tubes leaves the inductence/resistance of the 12A? tubes as the variable. This could be very good info. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13692 Registered: May-04 | . The variable is the designed in gain of the tube. The 12AX7 is spec'd as a 100mu while the 12AU7 is only 20mu. That is the rough spec and tubes vary from one to the next as far as how closely they stick to that spec with some falling slightly below to some a notch above. Even though the phase splitter is not used as a gain device the circuit calls for a certain amount of voltage out of the tube. If you step that down at the front of the amplifier, nothing in the following circuits will perform at spec. Consider the effect of stepping down a 1" water pipe to a 1/4" pipe and what happens at the output of the smaller pipe if you are feeding a series of sprinkler heads. The amplifier won't sound bad with the lower gain tube in the circuit and the difference in a unity gain application would amount to a very small difference in actual output from the entire amp. Probably such a small difference the gain controls have more variance in their actual setings than would the output of the two tubes. But the amp would only perform as intended with the correct tube in place. Running the wrong tube can also produce tonal differences in the amplifier. Quite a while back Kegger mentioned using 5751's as a step down tube with half the gain of a 12AX7 and while this application works, I pointed him to an article that mentioned how running lower or higher gain at any point in a circuit could possibly affect the tonal balance of the circuit. Even back in the 1960's Mac was using tightly toleranced components - as low as 1% in some cases - to ensure their circuits worked as specified. Mac never warranted their amplifier's performance with tubes not provided by them. Inserting the incorrect value of any component at any point ensures the circuit will not operate as intended. If you were using a Dynaco tube amp with 20% tolerances in some locations, the wrong tube might not be as noticeable. . |
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Platinum Member Username: NuckPost Number: 12743 Registered: Dec-04 | I remember Keggers issue, JV, but I recall that as being in a stereo amp, and not mono amps, which is a difference. I am still lacking as to how a splitter tube would be affected by the caps and /or reverse. In mono, the issue would sem to be simply pkase split, and I wonder which phase, + or -(ref) is affected? I am taxing the issue, and have neither the smarts nor the inclination to advance the issue too far, but the splitter tube thing is interesting. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13693 Registered: May-04 | . First, these are stereo amps (MC240 = two channel amp at 40 watts per channel [as opposed to a MC40 which would be a true mono amp but still push-pull]) bridged to play in mono. Other than one side of the waveform being placed out of phase against the other side by the operation of the "mono" switch these amps operate just as they would in stereo. (One of the old tricks was to connect a stereo amp out of phase at the input and then reverse the connection and restore phase at the outputs. This put less stress on the power supply and gave slightly better sound for cheaper amplifiers with lower quality supplies. The "mono" operation of this amplifier doesn't exactly accomplish the same thingt but the idea is the similar.) Second, a push-pull amp still requires a phase splitter whether it's a mono or a stereo amplifier. Push-pull operates with the positive going waveform on one side of the channel and the negative going waveform on the other side. That's why there are two output tubes per channel in these amplifiers. Two tubes per channel don't necessarily mean push-pull, you can have 2, 3 or more paralleled output tubes in a single ended amplifier. But the most typical arrangement would be one power tube for the "+" side of the right channel and one power tube for the "-" side of the right channel and then the duplicate of that tube compliment for the left channel. With this arrangement the signal is immediately "split" from one poisitive/negative waveform into two distinct circuits and later recombined in the output transformers. Looking inside the amplifier you would see two channels, left and right, each with two identical circuits for "=" and "-" sides. So the signal path of the MC240 has four coupling caps of the same value and four bias circuits of the same value, etc. http://www.kbapps.com/audio/schematics/tubeamps/mcintosh/mc240.html If you look at the small signal tubes like the 12AX7/12AU7/12BH7 in this schematic, you'll see the pahse splitter 12AX7 and then each half of the channel is using half of the following dual triodes. A dual triode is essentially two tubes in one envelope with the ability to perform its duties to either two separate circuits, two separate channels or be paralleled as two tubes in one channel for higher gain and/or lower impedance. Not all designers use both sides of a dual triode, particularly in pre amps where the circuits are often run as single ended (and class A) so you sometimes throw away a tube that is good on its other half. Of course to use that half you would have to rewire the tube sockets. The phase splitter was not affected by the capacitor failure. And the caps did not affect the phase splitter. These are two different issues with two different solutions. . |
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Platinum Member Username: NuckPost Number: 12750 Registered: Dec-04 | Gotcha. Good stuff. |
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Gold Member Username: KeggerWarren, MICHIGAN Post Number: 2780 Registered: Dec-03 | Hey guy's what up? Actually on the MC240 the first 12AX7 is not the phase splitter it is the voltage amp. The phase splitter on this amp is the following 12AU7 in the LTP style arrangement. The last 12AX7 is a buffer/follower to drive the outputs an really not the best choice for this duty, a 12AT7 popped right in that spot "should" be a circuit upgrade. The phase splitter is the critical part of the circuit in a push pull amp and the one that needs there values properly arranged in the circuit to do it's job correctly so subs are generally not suggested there. (also any direct coupled circuits can be tricky for subs) The first 12AX7 with it's gain of 100, using a 5751 instead with it's gain of 70 should end up being about the same gain with a 100K plate load on the 12AX7 and I would gather a guess to it being a better sounding and performing tube in that spot as well. Yep, it will perform differently then the original design and should alter the "sound" of the amp, some will like the change an I'd assume some will not, never know till yu try.  Cheers, Keg |
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Gold Member Username: KeggerWarren, MICHIGAN Post Number: 2781 Registered: Dec-03 | Also not all phase splitters are unity gain, the LTP style gets about half the gain a tube normally has in a straight single ended voltage amp type circuit, so it does have gain.. |
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Platinum Member Username: NuckPost Number: 12757 Registered: Dec-04 | Kegger! The stories of your demise seen to have been premature. Good post and quite timely. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13694 Registered: May-04 | . Kegger - Good to see you again. I'm working from memory here as to the description I was given of the circuit almost 30 years ago but I seem to remember the first single 12AX7 being the splitter (and serving also as a buffer in that function). The 12AU7 then served as a phase inverter. That part I sort of remember coming straight from the Williamson design handbook and only later being bastardized by cheaper amps saving on tubes and combining functions. But I don't remember this LTP style arrangement* you mention. I don't remember pin outs and I would stand a better chance of reading my high school French lesson book than remembering how to follow the schematic well enough to decipher this circuit - it has been 30 years since I used this information. Can you provide a link or some information about the LPT arrangement? Also why change the cathode follower to a lower gain tube? What's to gain there? Particularly since there are more good sounding 12AX7's then there are 12AT7's. NOS tubes might gain something (at the expense of something else) but the 12AX7 is still the go to tube for most of these purposes from what I remember and most especially in vintage designs. And I think you and I will still disagree about the value of the 5751 in a circuit. I tend to think it would, as MW states about the 12AU7 in that socket, take away some of the drive of the amplifier's sound. Granted the 5751 and the 12AU7 are drastically different tubes but I tend to prefer the higher gain of the original. And then I thought the 5751 was half the gain of the 12AX7 and the 12AT7 was 70. *LTP = Long tail pair? But that would couple this tube to the 12BH7 then, right? I didn't think you could place the phase splitter/inverter between the two devices. It's been a long time since I actually had to remember this stuff. Finally, what have you turned the Dyna's into this year? . |
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Gold Member Username: KeggerWarren, MICHIGAN Post Number: 2782 Registered: Dec-03 | I'll post more later as we have 1 of our annual/monthly audio meets I'm leaving to shortly. (we gather at a different members house once a month to have a few cocktails an audio) Anywho on the MC240 schematic u linked, the input tube or first tube or driver is a 12ax7 and it just the first gain stage of the amp, if you look there is only one out coming from the plate, no second or inverted it is just the straight grounded cathode voltage amp there in which it drives the following stage which is the LTP splitter then through differential stage to the follower. Here is 2 links to talk of splitters and the Long Tailed Pair, LTP, on the 70's I use schmidt type phase splitters which is a variant on the LTP. http://www.angelfire.com/electronic/funwithtubes/Amp-Phase.html http://www.bonavolta.ch/hobby/en/audio/split.htm No the issues isn't gain with the 12ax7 being used on the last stage as a follower as there really isn't any gain it's the plate resistance of the 12ax7 with leads to low current output an high output impedance, 2 things that are not good for a follower and quite the opposite of what they "are" good for, a 12at7 would do much better there in that regard. Also I'm not the biggest fan of the 12ax7, both for it's eletrical properties and it's sound, I'd much prefer using a 5751 where I "had" to use a 12ax7, but when I build or rebuild my own I use low gain an low plate resistance tubes which yeild more current, tend to be a bit more linear and require less feedback to get the job done, also I've found most to sound better. Just not the 12AX7 fan here, not to say I don't use them I do in my phono stage or gear that has them with no real easy or beneficial way to replace them. (just not my cup of tea though) Not a 70 by any stretch of the imagination anymore (I do still have the 2 Jan, 1 orig 1 mod) but here is a link to what I did using a 70's chassis to build a new amp on, only the PT used. http://www.audiokarma.org/forums/showthread.php?t=208576 Lately I've been into Single Ended Ultra Linear, but I'm going to convert one/pair into push pull. Cheers Keg |
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Gold Member Username: KeggerWarren, MICHIGAN Post Number: 2783 Registered: Dec-03 | You can place the phase splitter pretty much anywhere in the circuit. And most often placing it between 2 stages that are "steady" is a better place. |
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Gold Member Username: KeggerWarren, MICHIGAN Post Number: 2784 Registered: Dec-03 | 12ax7 is 100mu, 5751 is 70mu and 12at7 is 60mu. The big difference is in there plate resistances. 12ax7 is roughly 80,000 5751 is roughly 58,000 12at7 is roughly 13,000 So in a given circuit the 12at7 will garner more current, and quite often people don't realize that you can get more gain from the 12at7 in a lot of curcuits from the sheer voltage that isn't available to get the true 100mu out of a 12ax7 as the plate load should be say 300K or more to do so but if you do that and set your cathode/bias resistor for decent current the plate volts will end up way less 100 and loose all the gain you were hoping for with 12ax7. Also quite often I find 12AX7's being used in circuits then all this feedback to knock the gain back down to useable levels to where a low gain tube coulda been used in the first place with less to no feedback being "needed" in the end. Cheers, Keg |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13695 Registered: May-04 | . "Paralell Single Ended Ultra linear" Well, I recognize the chassis. But I don't think that's what Hafler had in mind. OK, I get the parallel. But single ended UltraLinear?!!! What's the point of that one? . |
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Gold Member Username: KeggerWarren, MICHIGAN Post Number: 2785 Registered: Dec-03 | You've got.. Push Pull Triode Push Pull Pentode and Push Pull Ultra Linear I prefer Push Pull UL for the power portion, the easy supply verse pentode an the sound. Well you have.. Single Ended Triode Single Ended Pentode So why not Single Ended Ultra Linear with all the same stated above attributes then I say. With going Single Ended UL you get a very simple circuit that let's pentodes perform in a single ended amp that doesn't have the typical overblown mids many find bothersome. (quite a flat presentation from this type of amplifier layout but keep the SE "sweetness") (And then obviously more power verse running triode strapped pentodes here to.) Pretty much all new SE output transformers have UL taps on them these days for pentodes. Some pentodes perform very very well in UL, and many are fine sounding in this config also. Just another way of running the output section that has been getting more exploring as of late. The Site DIYAUDIO has a tube section that can get rather creative at times with new things to think about and ways of doing things, I do not agree with all of of it, but it is nice to see people "thinking" and trying things not just rehashing the same thing over and over. One thing I like and have been experimenting with is using LED's instead of cathode resistors on driver or preamp tubes, no need for a cathode bypass cap and can be handy when your in the need or want for full gain from the tube, the amp I linked to uses that and you can "roll" out different ones with the sockets I installed on the driver board, you can use them to change the operating point of the circuit with different voltages and current properties as well. Cheers! ------ Nuck, good to see your still around, |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13696 Registered: May-04 | . "Some pentodes perform very very well in UL, and many are fine sounding in this config also." Is that what you meant to type? Yep! Pentodes have been performing well in UltraLinear since Hafler and crew introduced it in the late '50's. Most designers abandoned a simple pentode connection (and the Mac and Quad variations were available only under licenc) and more complicated) and we have seen virtually every new p-p tube amp with output transformers being done in UL for nearly 60 years. "Pretty much all new SE output transformers have UL taps on them these days for pentodes." That's almost too bad. I have less than favorable opinions of the ability to switch pentodes into triode or SE operation. UL was the point of combining the better qualities of pentodes and triodes. Beam power tubes IMO made both less desireable. I can't always agree with the idea of doing something just because you can do it. As a lesson that's fine but trying to build something the world has never seen and being successful at it are two very different things. . |
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Platinum Member Username: NuckPost Number: 12789 Registered: Dec-04 | https://www.ecoustics.com/electronics/forum/home-audio/576374.html This little flea amp from the Integrated thread is running the same arrangement, I think. Seems to review pretty well. And thank you Keg, still kicking here. |
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Gold Member Username: KeggerWarren, MICHIGAN Post Number: 2786 Registered: Dec-03 | Yes Jan not ALL pentodes work well in the UL config.. (and I'm quite aware it's been done for a long time and still by many) Well I think you just haven't experienced enough pentodes running in SE then as right now my favourite sounding amp is an SE pentode amp running in UL. As I said some pentodes make excelent devices running in SE, be that there Triode strapped or in UL mode, some are down right exceptional sounding.. |
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Gold Member Username: KeggerWarren, MICHIGAN Post Number: 2787 Registered: Dec-03 | It's not to say a SE output transformer that has a UL tap needs to be used with a pentode, or that the pentode has to run in UL, you can use a triode with the output or strap the pentode. Just that most new SE outputs provide the tap so you CAN run a pentode in UL if you want. |
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Gold Member Username: KeggerWarren, MICHIGAN Post Number: 2788 Registered: Dec-03 | Yah Nuck that little amp you linked to it does look like it is running Single Ended UL, I can't find a good PDF on that pentode but I do think they are "streching" there stated output power a bit there from what I can tell from tube "subs" that are out there like it. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13697 Registered: May-04 | . "Well I think you just haven't experienced enough pentodes running in SE then as right now my favourite sounding amp is an SE pentode amp running in UL." Yep, I probably haven't experienced enough pentodes running in SE. I've not been impressed by the few I have heard. That doesn't comdemn the entire idea just because I haven't cared for two amps it just means I haven't been impressed by those two amps. I do, however, fail to see the point of the idea and maybe that's my stumbling block. Kinda like sticking a hopped up small block Chevy in a VW bug - I never saw the logic in that either. Pentodes do one thing, SE does another. (But send something down, I'd love to listen.) I think you and I have always been after something a little different in our systems and the hobby. You like the smell of a hot soldering iron.  Since you've found tubes you've also found a liking for constructing things with tubes. That just never finally appealed to me. I stopped reading the DIY tube section a long time ago because I just couldn't get interested in what was happening there. No insult intended but there was a fair amount of mental m@sturbation when I last looked which was years ago and long before I sold you the Dynacos. Actually, that was partly why I sold you the Dynacos. When I said I couldn't agree with doing something just because you could I was referring to this current trend towards creating a "sound" from your system and then switching that sound at a whim. That seems to be a big marketing trend right now and I am not much in favor of this for that and that for this. If you don't like pentodes for this album, switch to triodes. Don't like UL, switch to SE. I've always thought this was about establishing priorities, going after the music and not the equipment and knowing what got you where you wanted to be. This isn't, IMO, about whether you'd like more whipped cream on your Dianna Krall CD and less on your Led Zepplin reissue or how the amp soundstages. That's where I've most often seen DIY heading over the decades I've been involved in this hobby. LIke you say, it's about making an amp "sound" a certain way. And the DIY'ers always have a different sound they're after. I don't want them to stop, I just am not interested in most of what I've seen come from the DIY crowd. Some items do make me sit up and think but many seem to be just exercises in what a particular tube or transformer can manage and then move on. Fun for some but not me. I glad you're having fun, Kegger, you have even, from what I've seen, developed a bit of a reputation as a tube maven. But I can't get interested. When I hear about "more current" from a tube amp - and I've heard it for quite awhile now - I just think that's not what tubes do. Tubes do voltage well and speakers that want current aren't in the same market as tube are. Even "more current" within the amplifier I just can't get interested in. Maybe I'm just not understanding it as well as I used to. It seems more like the guy I heard at last week's show; he had spent 14 years "perfecting" his one speaker design. Geez, after about the eighth year I think I would have said maybe this isn't what I should be spending my time on. (The local Lone Star show is mostly about DIY and I've been amazed at how differently people hear their own creations.) Tubes do voltage exceptionally well and there are speakers that work exceptionally well with voltage, they just don't get placed into the mainstream much today because of the prevailing market where certain designers have moved the hobby in a particular direction. I read about Nelson Pass's designs and I think, "Now there's somebody who isn't doing something just because he can or because it will sell." That interests me. If I could ever convince myself to use transistors, I might try one of his designs - but then I'd probably have to change speakers since my speakers don't work on current supply. I've been more interested in single drivers of late and I listened to a pair of field coil systems last weekend that I thought were impressive in many ways. So I'm kind of in my Dr. Harvey "Gizmo" Rosenberg phase. I have no intentions of giving up my Mac's because I still very much like what they do but what was old is new to me. (I really can't tell you how many times I seen DIY mods to the Mac amplifiers.) Again, IMO, the largest part of the hifi industry has been led down the wrong path for the sake of convenience and lower production cost. So my sentiments are with the DIY'ers, just ... I don't know, are there old DIY'ers? I've always got the impression the constant change for the sake of change sooner or later wears off and you've seen most of this stuff before. I do think it's a hoot that you're doing your amp on a ST70 chassis. And I'm glad to hear you stilll have one stock. So what are you doing with pre amps nowadays? . |
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Gold Member Username: KeggerWarren, MICHIGAN Post Number: 2789 Registered: Dec-03 | I would agree Jan, you and I are different on many accounts, be it a "sound" were after or tinkering or many other things, it doesn't mean we can't agree to disagree though. (I'm certainly not trying to make anyone convert over to my beliefs, just expressing them when I see or feel the need to chime in on a particular subject I believe in) I think you know from the first we talked I was the kinda person who could never leave well enough alone, and if it was good there must be some way to make it better then. (I haven't changed since then and never will) Also when I get into something I want to learn and try it all within my power, if my power doesn't have the capability I try an learn what it will take to get there, that is my passion. One thing you mentioned long ago was the old school tube sound an new school tube sound, I believe a lot of that has to do with current I mention when running tubes, so at the lower currents you get the old school and sometimes tuuby sound and new school being more on the analytical side, I try an ride the fence on that one, maybe a bit more current but less feedback, those are blanket statements an not always are true either. I have my beliefs/feelings and biases about certain circuits and ways of doing things as well, I'll look at something and feel well that isn't what I do and probably will sound a certain way and not to my liking, sometimes that is true and sometimes it is not, so I do 'TRY" and keep as open a mind as I can. Tubes facinate me, I love how things go together and the construction process, there is always something on my bench, I have a complete system there an listen to music more there then in my main system. I also get a lot of music in at our gatherings once a month on many different systems, it is amazing sometimes the difference of oppinion on how well the systems play, an I meen HUGE differences from the best I've heard to worst I've heard from people in the same room listening at the same time. There is no one pleases all type setup. (from great vintage to great new to DIY we have a pretty good group here) I've got many different speakers, some I really really like the speaker and at times I have matched or built amps ecspecially suited to there abilities, lately I've been at the lower side of power so my speaker needs and wants change as well, my latest is a 2-way 12" woofer (pioneer HPM 100) mated to a JBL waveguide running some selenium compression drivers for some decent sensitivity and easy to drive. (Another amp I feel is a great performer here is my Push Pull triode 6AV5) Some call what I do not the right way to go about it, but I say if I can I want to try then. (I have no problem failing, it certainly happens, that just makes me more determined) A lot of people are not into the building or understanding, they just want there music, I have no problem with that an in some ways wish I was the same, certainly would be a few less headaches I'm sure.. There's a lot of new DIY tricks an fads I just don't buy into, but I feel I need to try them as much as possible so I can say for myself whether they really do work or not though. I've found some things I like, circuits I feel perform very well, a genre of tubes that do what I want and tend to lean that way when I build or rebuild something. In Michigan and the surrounding Ohio area there is a lot of well respected designers and DIY to where I can and have learned a lot from, I am blessed in that regard for sure. There are plenty of old Diyers and many well respected older "teachers" of the trade, some have websites dedicated to it with very loyal followings, newer books written by some of the greats from today and the past. (they are trying to keep it alive and well) Yes I have my heavely modified ST-70, my stock ST-70, a chassis I got after a rebuild for someone so I installed Acrosound TO-300 tranny's on an run 6BG6G sweep tubes! Then the one you saw I got the chassis after a guy bought a new chrome one because that one was so pitted and rusted, I had it sand blasted then I painted it to build an amp. Preamp I'm working on at the moment is a plate choke loaded either 12B4 or EL86 in triode using a tube regulator setting the supply voltage at a steady 150v B+, the plate choke is basically a choke like you would have in a power supply but has the very high Henry rating and takes the place of your plate load resistors, they are much less of the DC resistance then your typical plate resistors so drop less voltage but get "full" gain. (many feel using iron for plate loads in preamps is the road to best sound, we'll see) I can't have just one system or even just 3 for that matter , I've got some single driver stuff as well, I feel the intimacy of that approach is very addicting, those SE amps work well with that combo to.. ..What drivers or speakers are you messing with? (Man that was a JAN sized post) Cheers, Keg |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13698 Registered: May-04 | . " ... there is always something on my bench ... " Yeah, I remember the pictures of your bench!  Link a few of the old timer DIY sites if you would. I'd be interested in seeing where the "hippies" I knew in DIY are at today. You probably remember my contention that transformers went out of style because they were more expensive to produce and far more costly to ship across the ocean when Japan came calling with transistors. Yeah, I'd say chokes and transformers would be approriate for certain applications but they get costly very quickly if you want to do the job right. If you don't, then resistors and caps are better than a lousy transformer. I can't bring myself to say any sort of transformers are worse than direct coupling (even OTL's) but cheap output transformers are still cheap output transformers. I don't know the 12B4. But this running pentodes in triode I don't get. It just doesn't make sense to me and seems like another fad that will pass - sorta like alkaline battery powered screwdrivers. Maybe in that same vein it will turn into something new but I'll wait and see. DIY always has fads IMO. But how are we ever going to know without Billy Mays pitching it? That ain't gonna happen now. I remember the discussions about old and new school, neither of which I felt was exactly right because they both went for a "sound" or at least could be classified with a type of sound. I still see a lot of people wanting a "tube sound". You can't remove yourself from "a sound" - unless you become a measurements tell us everything type of listener who has already convinced themself everything pretty much sounds the same then they hate "toobs" in the first place and tell me I'm stupid for liking those distortions they can measure. Yeah, right. Enjoy your Pioneer receiver. The show MW and I went to last weekend had a speaker builder exhibiting a cheapo system with an $89 Insignia receiver and a pair of Dayton kit speakers. He said it was just for fun to show how you could get "decent" sound for a few dollars. I really had to disagree with his assessment but I just exited the room and allowed him to go on thinking what he felt was good. He is right, they aren't plastic speakers that sound like cr@p and he admitted it wasn't hi-end but thought it served a purpose for his impoverished musician friends. Maybe. We all listen different and have different goals, I suspect the guy showing the 7'X4' electrostats hasn't spent a lot of time with a 300B lately. I started out a couple years ago with a pair of Zigmahornets by Dave Merrill. Little 4" drivers that he designed and had custom built for him in small quantities. They have a pretty good reputation and I wanted to do a quarter wave system but needed something more than another 82-84dB system. There were too many Fostex systems around to build just another one of those and most of those drivers require some sort of baffle step to get rid of the rising mids. The Merrills sounded nice but the basic cabinets had too many resonances for my ears and didn't give the right spacial information. But with the Mac amps the mids were top notch and the high end tended to simply "exist". And the system did timing and pacing as well as any electrostat I've heard. Another member here had ordered a similar set of Dave's drivers and then decided he had too much going on in his life and wasn't going to build the systems so he sold me his drivers. I used those with my existing drivers to build a dipole quarter wave pipe using a configuration presented in AudioXpress a few years back, dropped the F3 down half an octave without giving up efficiency. Pretty simple stuff, use the basic TS parameters (finding them was the most difficult part since Merrill didn't supply any information) and read off the graph for the length of the pipe and start cutting MDF. After that its putting stuffing in and taking a little bit of stuffing out, putting in and taking out and phutzing with the port to get what you want. No coming in contact with 600+ volts, no wondering were that wire was supposed to go or how it touched the chassis and fried the wholedamnthing. Merrill passed away a few months back but I see a new distributor has taken over his designs. I'll watch the stuff they do since Merrill's designs have such a good reputation and he was working on a new system when he passed away. I kind of have my eye on a quarter wave Lowther sometime but I have too many other expenses right now and I'm happy with what my system produces. I've liked the open baffles I've heard at the show the last two years. But I'm just not much into crossovers right now. I like the coherence of the SDFR's and have trouble warming up to most multi-ways. I built a few subs but that's still just make the numbers match on paper and then check the distance from the fence to the saw blade. Tim Forman was on the forum a few years back and he gave me some information on a driver (that is also now discontinued and the company decided not to fight the politics/BS/insanity of people blowing your stuff up that goes with certain parts of DIY). So, if I get stupid with my system one night, I could be screwed big time since there are no more replacement drivers for most of my speakers. I try not to be that stupid. Is the pre amp line only or are you doing phono? Based on the Dyna's? . |
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Gold Member Username: KeggerWarren, MICHIGAN Post Number: 2790 Registered: Dec-03 | Yah the bench looks about the same as before, just maybe even mooore crap on it. When I get a chance to dig up some of the old time diy sites I'll post them, there's a guy John Broskie that I believe is an older gentleman that keps a running blog here. http://www.tubecad.com/ (the tubecad journal) respects and refers to old designers. Fullrange speaker without xover certainly is appealing, some work quite nicely aye? Sounds like you've had/still have some experimenting going on there, glad to hear it. I would also agree if your going use a piece of iron, ecspecially plopped right square dab in the signal path I'd hope it to be a good one, and yah those plate chokes I have are suppose to be pretty well made using some top quality construction materials to. The 12B4 is a 9 pin triode with the gain of roughly 6 and plate resistance of less then 1k, so a straight single ended type circuit with no cathode followers and or feedback are "needed" to get decent output impedance plus drive for the amp, the EL86 when strapped triode is basically the same spec as the 12B4, same gain/plate resistance, will draw roughly the same current an I believe only two pins are different so are easy to swap into the circuit so I can try both. I've ran the EL86 triode strapped both as the driver in an amp and as an output in another amp, I do like how they perform there. The preamp is just linestage, I actually did some mods to my EAR 834P phono stage a few years back (not my changes but the well documented thread on audio assylum) and it is probably the one piece in my system I just leave alone, I feel to better it would really take some time and effort, and I'm just plain happy with how it works with/on my Denon table coupled to the Signet cartridges I've become fond of. If I were to build a phono pre it would probably be based on that same design, maybe use different tubes, right now it is an Amperex 12AT7 first stage, to a Mullard CV4004 (12AX7) for the RIAA to an RCA blakplate triple mica 5751 on the output. Works well. I hear yu on not having backup parts for things you like, I try an have spares of any one thing that get's serious play in one of my systems, (but I need even more room now)  Not that your serious about doing speaker projects but the Partsexpess Woofertester is a great tool that hooks to your pc then test any driver an it spits out the TS specs in an easy to understand interface, it's like $100.00, what else is nice you can test whole speaker systems or just test boxes to get impedance plots, quite handy for us toobies! |
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Platinum Member Username: InsearchofbassYork, Pennsylvania Post Number: 11732 Registered: Jun-04 | I would like to buy a decent tube amp to get my first introduction to them. Any suggestions? I have some 4 inch fostex speakers to try it on if need be. Model ss -1.1. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13995 Registered: May-04 | . Received this in an email the other day; "Dear Music enthusiast: We have acquired a quad matched set new old stock, original boxed RCA 7581A. This is equivalant to 6L6GC, 5881,KT66. The price is $399.97 for the quad set. Test conditions are: plate 400V grid -48 results 1) 22 ma, 2) 22 ma, 3) 21 ma, 4) 22 ma ma=miliamps Another excellent offering for the more budget minded hobbyst are the Valve Art KT66 cryo grade tubes which are an exact copy of the GEC KT66. These are the best KT66 currently produced and are only 62.95/matched pair. Thanks for your past business and check out our web site when you get a chance. Ken Chait WWW.TUBEMAN.COM" . |
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Silver Member Username: HawkbillyNova Scotia Canada Post Number: 684 Registered: Jul-07 | I received a similar email Jan. BTW, I recently changed did some tube changes in my amp and cdp. I replaced the Tungsram 6922's with some NOS Amperex in the cdp, and plopped in some NOS Sylvania EL84's in the amp to replace the Harma's that have been in there for over a year. I got them from Andy at VTS. I particularly like what the Amperex's do in the cdp. If you've got a Minimax, it's an excellent combination to try, and the price wasn't crazy....I think around $150 for the pair. |
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Platinum Member Username: NuckPost Number: 13633 Registered: Dec-04 | Sidebar... Some people would just die if they heard $150 for a pair of tubes for hifi. But they have receivers, so... $400.00 for a quad? Is this a fair price for this set for a stereo amp? 6L6's are usually used in quad's in monoblock amps, yes? |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13997 Registered: May-04 | . Overall, the Amperex 6922's are probably the best of the bunch though there are a lot of varieties of Amperex 6922's and their sound might not suit some systems. A while back I acquired a set of Amperex 6922's for my AI pre amp to replace some Sylvanias I had been running in the phono side. I had a set of Amperex 6922's that were NOS when I bought them in the early '80's. I got them then for $20 per pair and they now sell for about $200+ per pair. There is a difference in the two Amperex tubes but the most recent additions better fit my current system than do the Sylvanias. The tubes advertised aren't 6L6's. They are 7581A's which is an "equivalent" to a 6L6. Different applications though most would be drop in replacements. You need to check the bias current and plate voltage on your amp, the suggestions for the tube's preference which can be determined by the transformers capacity and the plate voltage and current the prospective tube sounds best at vs. the ideal tube for your amp. This tube might produce higher or lower output than another similar tube so "equivalent" is with some cautions. You should be able to buy a very nice set of new Svetlana Winged "C"' 6L6's for about $120 USD for a quad set, lesser tubes for a few dollars lower priced. They aren't NOS but they are 6L6's which is the "kinkless" equivalent to the British KT66. The GEC KT66 was a very nice sounding tube. If your amp has fixed or auto bias set up, you don't require a matched set if you're just replacing an existing tube or tubes. For NOS RCA's $400 is not bad. If the amp were a push pull monoblock, it might require two tubes per amplifier. Depending on the manufacturer two 6L6's in pp would get you somewhere between 30 - 55 watts with 55 watts being a very hard (and hot) drive on the tubes which would reduce their lifespan. The more tubes wired in parallel, the higher the output power. . |
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Platinum Member Username: NuckPost Number: 13638 Registered: Dec-04 | Test conditions are: plate 400V grid -48 results 1) 22 ma, 2) 22 ma, 3) 21 ma, 4) 22 ma ma=miliamps 400 on the plate must be getting these tubes pretty hot indeed? |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 14000 Registered: May-04 | . Depends on how you're using the tube and what tube you're using. 600V would be very hot and beyond anything I know a 6L6 can withstand for long. 550V would be hot and still beyond most 6L6's if you want long life. 420-500V would be average I'd say and well within the limits of any 6L6 tube and good for a push pull class AB amp. Using an "equivalent" tube is sometimes due to the tube's specs and what it was designed to do and for whom. In the US most of the numerical designations such as 5771 and so on are originally military spec tubes that would likely have somewhat different specs than the 6L6 variety or the KT's. However, people buy the military tubes thinking they must be better tubes and often they do not perform as well as the audio tube due to the specifics of what the military tube was meant to do. One more reason the "sound" of any specific tube is circuit and tube dependent. The question with higher voltages becomes the quality of the ps and the power transformer. Bias voltage would be more a factor in power output and tube life. -48VDC is average for an adjustable bias configuration if I remember right and should be on the low side of the tube's potential. The 240's run -55VDC in a fixed bias mode and run cool at idle. http://www.guitaramplifierblueprinting.com/Tube/6L6GC-svet.pdf http://www.tube.be/6l6.html http://www.guitaramplifierblueprinting.com/datasheets.html If Kegger stops by, he should have better information though I don't think he has done much with 6L6's - they tend not to be the tube many people use now days in audio, they lack the power grunt of a 6550, the sweetness of an EL34 and the faddishness of an EL84. They are still the favorite of a lot of people with both guitar and hifi amps though, VTL used to do a lot with the 6L6 and the KT66 is a European favorite for its highly musical sound. Find a guitar player with a beat up blues amp and it will probably have 6L6's in it; http://www.guitaramplifierblueprinting.com/files/Blues_Deluxe_Schematic.pdf. . |
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Gold Member Username: ExerciseguyFort Hamilton, NY United States Post Number: 3046 Registered: Oct-04 | http://www.unplggd.com/unplggd/product-review/product-realview-acoustic-research-av100b-tabletop-radio-with-ipod-docking-station-066058  |
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Gold Member Username: ExerciseguyFort Hamilton, NY United States Post Number: 3047 Registered: Oct-04 | ...I wonder if you can bypass the internal speakers and use it to fire-up some external ones? 10WPC ain't too shabby? |
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Silver Member Username: HawkbillyNova Scotia Canada Post Number: 797 Registered: Jul-07 | Thought I'd post a link to this article. Probably not particularly informative to some of the seasoned tubeheads here, but I found it one of the best and well written articles on basic tube amp design that I have read. Eddie Vaughn has a very loyal following for his amps. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 14478 Registered: May-04 | . That's a fairly good article, CH. It would be a good primer even for those interested only in solid state gear. It's well worth the time it takes to read. I do detect a patisanship in the writing but overall for an eleven page document it covers the bases well and clears up some of the often times confusing details of construction between a SE and PP amplifier. Terminology which might be encountered in any discussion of the two topologies is covered in sufficient detail to provide a groundwork for understanding how the amps might be explained by a more evangelical retailer. It has a good beat and you can dance to it. I'd give it a 4. I take minor amounts of objection to only a few conclusions drawn by the author. The first of which is the line; "Human psychoacoustics do not obey the laws of science very often!" Not that I absolutely disagree with the statement, it is an idea most experienced listeners should be able to agree with on principle if not from actual experience. It's just that I find such statements to be open screen doors to those individuals who simply do not care to understand which laws of science are being somewhat disobeyed. The article's final quotation from van der Veen is too often abused by such individuals as a permission to ignore the most basic of rules for how we get from live performer to perceived reproduction. IMO it is a shame the attitude "My ears telll me everything I need to know" has been allowed to fester in the audio community for it is all too often those who do not even understand how "their ears" perform their assigned function who then hide behind the words of those who best understood just how to use their rational mind. Secondly, I would say the article gives short shrift to well designed, classic and enduring alternatives to the simple SE vs. PP debates. Vaughn appears rather derisive of the Golden Age tube designs and of those who built upon their foundations without at all explaining the circumstances they were attempting to overcome. His absolute dismissal of "specs" is discouraging for the reasons mentioned above. To say the debate is strictly between SE and PP amplifiers is too simple and factually incomplete. Not mentioning UltraLinear, Unity Coupled or Current Dumping amplifiers designed by (ostensibly) Hafler, McIntosh and Walker is the equivalent of not mentioning De Forest or Tesla at all - all of whom the author did not mention at all. It is a short ten page article and it packs a good bit of information in those ten pages. My only wish would have been that the author would have provided a more clear path to follow towards the next argument(s) regarding tube amplifiers and that his partisanship for a particular topology would have been reined in somewhat more than he managed. However, he is selling a SE amplifier on his site so there is only so much one can expect I suppose. The Chevy salesman doesn't recommend a Honda. I would also suggest everyone read the article on damping factor found on Vaughn's site. His "links" page is also filled with plenty of informative sites. Thanks, CH. . |
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Silver Member Username: HawkbillyNova Scotia Canada Post Number: 800 Registered: Jul-07 | Yeah, I thought he covered the basics very well....enough to help me understand some of the basic building blocks better than I had. There is some interesting differences between his views, and that of say Steve Deckert. I doubt you'll find two designers to agree on everything, but I always find it interesting to see what is agreed on, and what isn't. As you point out, you always have to be aware of what the author is selling, as that may lead you to his prejudices. |
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Gold Member Username: Rick_bOrlando, FL Post Number: 1447 Registered: Dec-03 | Anyone interested in my Sophia Electric "Baby" and Spendor S3/5's shoot me an email. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 14714 Registered: May-04 | . You're selling? |
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Gold Member Username: Rick_bOrlando, FL Post Number: 1449 Registered: Dec-03 | Yes sir. |
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Gold Member Username: T_bomb25Aurora, Colorado United States Post Number: 2221 Registered: Jun-05 | Love el84 based units such a different beast from el34's. |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 3961 Registered: Feb-07 | Anyone have experience with SET 300B tube amps? Opinions? |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 14914 Registered: May-04 | . That's an awfully broad question. Even distilling the topic down to just a 300B as a triode power tube leaves plenty of room for pages of discussion. Try being a little more specific and maybe a quick answer can be made. Otherwise, considering a generic SET power amp w/300B's, they are the classic modern SET tube, the most popular triode for the purpose and the tube that essentially resurrected SET's as a viable audio product. Those who just can't go along with the pack won't care for the 300B's overall musicality and sweetness and want the 2 1/2 watt "grunt" of a 2A3 or oddballness of owning a directly heated triode amplifier (the true triode fans believe this is the only way to reach audio zen). The 300B is generally characterized as having a softer bass response (due to a high output impedance for one thing), slightly (classically) forward mids with a somewhat less emphatic high end than many other triode power tubes but the musicality is what keeps people attached to the tube. Vocals through a 300B are the bee's knees! The overall character of a 300B tends to make it a good partner for high efficiency speakers using a SDFR or horn loaded drivers. With a solid 8 watts output a 300B amp can produce good SPL's with excellent dynamics when coupled to a 100dB horn loaded system. Much of the characteristic 300B sound can be altered by using it in various circuits or as a paralled output tube, or in a push/pull design (not many of these around) or as a low level tube in a pre amp. The quality of sound between the various 300B tube manufacturers is ridiculously variable and, of course, only the high priced spread gets universal acclaim as being worth your time. The selection of 300B tubes has expanded somewhat over the last fifteen years with the NOS and now the reminted Western Electrics still being the most preferred version. The new WE tubes do not come cheap (NOS versions become a choice between buying the tube or getting the Ferrari tuned up) and most come with no more than a 90 day warranty; http://www.gcaudio.com/cgi-bin/store/showProduct.cgi?id=188 You can just about bet no new amp you buy will be using the WE tubes as OEM outputs. This leaves you with a decision to make, upgrade to the far better tube almost immediately or live with less than spectacular 300B sound for as long as your bank account holds out. Some will tell you, and you'll have to decide for yourself, when paired with the right speaker and front end, bad 300B sound is better than any other tube's best sound. You can also count on being able to use any 300B power amp as a not very efficient room heater. A 300B SET amp is possibly not the best choice for a small room in Texas in the summer but may be all you need in the winter. I would defintiely recommend a hand's on audition and the opportuntiy to live with the amp for at least a weekend. Most SET amps are higher maintenance than a pentode or beam power tube in push/pull Ultralinear operation. They require more attention to detail and less OC personality on the part of the user. I would highly recommend you not buy a SET amp on line, unheard, or without solid dealer backup. . |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 3967 Registered: Feb-07 | I've noticed that most (or all?) 300B amps tend to be pure Class A. Is this by necessity or by design? Would this have to do with the SET amp being considered sounding "better" than other amps? |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 14915 Registered: May-04 | . Go back and read my post again as I have added a paragraph at the end you might have missed. A single ended amplifier can only run in class A by the very definition of "single ended". Think about how push/pull amps came about, they were the result of a desire for higher output power from a single tube. By splitting the duty cycle of a tube to only one half of the signalwave the tube is more efficient overall (not looking at the various negatives of push/pull design) and can produce more power during that cycle than when all of the tube's power must be devoted to producing the entire signalwave. If you'd check a tube directory you'd see the various output wattages available in the different classes of operation. http://www.drtube.com/tubedata.htm#BPTetrodes http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm Most SET amps also use no - to minimal - negative feedback. Triodes have a self cancelling nature that dispenses with the need for traditional feedback circuits to reduce harmonic distortion. (Some listeners still claim it is the existence of specific harmonic distortions that make tubes, and triodes in particular, so likeable. IMO they are wrong. Sometimes - often actually - you'll see the solid state lovers telling you that any amp with more than 0.001 THD is adding stuff you don't want and therefore "toooobes" are not accurate - laugh at those people and walk away.) If you can find a current copy of "audioXpress" magazine, there's an intersting article on tube vs transistor sound. Of course, negative feedback can also be used to both increase the gain in a circuit and to lower output impedance so negative feedback becomes a controversial "topic" in SET's. I doubt you'll find a SET amp with global NFB however, any NFB employed will be contained within an individual circuit. Don't fall into any way of thinking about "this" being better than "that", it's all trade offs. Class A operation doesn't guarantee much of anything other than the system will run hotter than an equivalent class AB circuit. Class AB done well is a very good way to go while class A done not to your liking can be excruciatingly dislikeable to the point of painful. I used to sell Threshold amps with Theil speakers and I thought the combination was horrible, I couldn't stay in the room. Think "system sound", not class A or Ultralinear or any other sort of sound. Class A doesn't have to sound a certain way, most of the benefits of class A operation IMO lie in the crcuit simplicity inherent to the design. SET then takes this to the next level with a minimalist parts count in any well designed SET power amp. . |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 3968 Registered: Feb-07 | Thanks Jan. That actually all makes sense to me. Is not Class A considered better than Class A/B (I know you hate the "better" term) since there's not the distortion introduced due the switching from A - B operation? |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 14916 Registered: May-04 | . Trade offs. Trade offs make life interesting because you get to choose what's most important to you and what is less important to you. Then, every now and again you find something that knocks all of your preconceptions about what is and is not important right into the corner needing a skilled trainer and a forgiving referee. Go read the article I linked to which covers the various classes of operation. You'll see there are "degrees" of class A operation which allow for more or less swing from positive to negative bias. Where the bias is set determines where the cutoff between positive and negative waveforms occurs in an amp or how the amp handles various loads. Typically, you can bias a pp amp a tad hotter to get closer to class A operation or you can roll the bias back to cool down the sound and extend tube life. Trade offs. If the output devices run more towards class A operation while still being an AB circuit, then switching noise can be minimized - not eliminated but minimized - to possibly non-objectionable values. A typical trade off here would be shortened life of the outputs, higher harmonic distortion levels and higher heat output. In a pp amp you can apply UltraLinear, Current Dumping or Unity Coupled circuitry to bridge the gap between triode and pentode sound, provide higher current without sacrificing high voltage or to gain higher overall "power" with lower distortion and longer tube life. Choosing between triode, pentode and beam power tubes gives you a choice of which distortions you can live with and which you prefer less. Negative feedback and its application provide degrees of control (and further trade offs) over distortion. All sorts of schemes have been devised to provide certain characteristics to an amplifier's "sound". Most of these circuits or methods of connection involve lowering distortion while maximizing power. If the more powerful amp runs in a lower power envelope than the less efficient amp it is probably running in its most linear range. Then the trade becomes the existence of some amount of switching distortion vs overall harmonic distortion at low to high (or even mild clipping) values. IMO switching distortion is more problematic in transistors than in tube amps. Tubes do not completely shut down when switched off while transistors do. Switching in mid-cycle then becomes more noticebale - at least to my ears - in a solid state amp. But maybe I'm also hearing the high order harmonic distortion products of that particular amp instead of just switching distortion. Or just the nature of the output devices selected by the designer/manufacturer. I can change output tubes to arrive at the sound I prefer, this is not so easily accomplished in a solid state amplifier. And, in the end, lot of this becomes academic as distortions have been lowered all the way around over the years. Possibly it's something else entirely that draws me to tubes and away from solid state. The same goes for class A vs AB, maybe there's something else that is causing my reaction to whichever amp I'm hearing. There are too many trade offs and too many variables to say "this" is what I object to. The problem becomes trying to tie the "sound" of an amp to any one or two things you suspect it does. Switching distortion in a well designed amp certainly can become benign to all but the most ardent fan of class A. And then, since there could be several causes of whatever is heard as the sound of a particular amplifier, switching distortion might just be a convenient place to hang a hat whether you like or dislike an specific component. Tell me, are you aware of switching distortion or have you just been told it's present in a class AB amp? If you don't know switching distortion is what you need to get rid of, then making a jump to an amplifier with other trade offs might not be the best idea. Most people I think will tell you it is the simplicity of the class A circuit and the consistency of one output device that appeals to them in class A. No two output devices are exactly linear in their operation, therefore, when you switch between two devices in class AB you might be hearing the inaccuracies of each device handling either side of the waveform. This becomes more of an issue when you are using tubes which age and consequently alter their output waveform in inconsistent ways during their life compared to transistors which essentially do not. It becomes even more of a problem IMO if the transistor amp has had repairs and "equivalent" output devices have been substituted. Tube amps can have new tubes inserted which then are more closely matched. Single ended amplifiers (can and usually do) eliminate the issue of multiple non-linear devices but the circuit introduces other trade offs. Remember, single ended means the amp operates in class A - it can be nothing else because there's only one output device handling both sides of the waveform, hence "single ended". All high end pre amplifiers operate in class A but they might not be a single ended design (most are though). Class A does not mean the amp is single ended, there are far more push/pull class A amps out there than SE's because of the need in modern consumer audio for high power output. In transistor class A amps most of these push/pull circuits are also paralleled multiple output device designs. This results in even more trade offs when what you thought you were buying was a simple circuit. Of course, you can find rather complicated class A amplifiers if the designer so desires- the early Nelson Pass designs were not so simple in nature though he is a champion of class A useage. No, I would encourage you not to get caught up in one thing being better than another due to its name or explanation or anything else. My thinking on this has for decades been you can make anything work well if you have the time, energy, money and the desire to make it work well. That still doesn't make it a good idea but you can create the one item that disproves all the other designs just didn't try hard enough, long enough or pump sufficient money into the design to overcome inherent shortfalls. This sort of design process usually becomes the overly complicated monster that consumes a designer's life and takes twenty years to bring to market only to have been superceded by the simpler, more straightforward designs that have come in the meantime. Read the DIY amp pages and you'll see lots of designs based on the oddball tube someone has found laying in a shop. Well, there's probably a reason the market didn't rush to using that tube five decades ago. It's the music that counts, not the technology. If a particular class A or SET or 500 watt class AB, solid state push/pull amp floats your boat, then that might be the component to buy. Of course, if you don't have your musical priorities in line, it might become just another boat anchor you're trying to sell on Audiogon in a few months. IMO audio should not be a flavor of the month hobby. . |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 3969 Registered: Feb-07 | Thanks for the explanation Jan. I'm learning lots. Some of it goes over my head, but I'm still learning. Good stuff. Up until last week I didn't even understand the difference between PP and SET. I read an article (that I think you provided) that gave a good explanation of the differences, as well as explaining negative feedback. |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 3987 Registered: Feb-07 | So I had a 300B SET amp show up yesterday. I took Jan's advice and got it on a trial basis with solid dealer backup. This is the dealer I purchased the KT88 amp from that really wasn't happy with. He offered to take the amp back and send me the SET before I'd even returned the other one. Very impressed. Anyway, this amp sounds GOOD. Like, really good. I'm running it with my MA RS6 speakers (91 db), and it actually goes quite loud for only 10 watts. Not that I'm really interested in it going loud, since I listen to music at sane levels after the kids go to bed. The soundstage is huge, and the sound is not at all what I've heard 300B amps sound like (mellow, lack of bass, etc). I've even listened to Metallica with it, and to me it sounds pretty darned good! |
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Platinum Member Username: NuckPost Number: 15081 Registered: Dec-04 | If you have read up on the basics, Dave, then you know that those 10watts are much easier to work with than other designs, and should you push it a bit, the distortion won't cause breakup or fatigue. If you keep within the limits, then none. Next up, you might be able to try some HE speaker designs, maybe like an Audio Note or such. First watt dynamics are a very strong point with amps like your new SET. Enjoy!!! |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 3989 Registered: Feb-07 | I am my friend, very much! |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 3990 Registered: Feb-07 | I haven't tried any other speakers yet, but the MA's seem like a very sweet match with a SET amp. I'll try the Sttafs too eventually, but with their 88db and greedy crossovers, it might not be a great match. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 14926 Registered: May-04 | . If the amp has a four Ohm tap, try running your speakers from there. This will lower the overall output impedance a bit and might be a better match for the MA's. Otherwise there could be a slight congestion in the lower mids due to Ohm's Law. . |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 3991 Registered: Feb-07 | Yup, the MA's are rated at 6 Ohms nominal, so I figured that the 4 taps would be the way to go. Listened to the amp for about 6 hours today ("work from home" day today). This amp sounds really good Jan.... I'm happy. |
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Silver Member Username: HawkbillyNova Scotia Canada Post Number: 940 Registered: Jul-07 | What specific amp are you enjoying there David ? |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 3992 Registered: Feb-07 | Its a Grant Fidelity A-534B. Really a rebranded Yaqin amp by a distributor here in Canada who has gone above and beyond to make me happy. http://grantfidelity.com/site/A-534+300B+SET+Tube+Amplifier |
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Silver Member Username: HawkbillyNova Scotia Canada Post Number: 941 Registered: Jul-07 | Interesting. I'm glad you're digging it. If you're liking it now, you should be loving it after you get a few hundred hours or so on it. |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 3994 Registered: Feb-07 | That's what I'm thinking too. Had it running most of the afternoon and evening yesterday, and either I'm getting used to the sound of it, or it's starting to sound better already. |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 4002 Registered: Feb-07 | Dropped some Gold Lion K77's and a pair of JAN Phillips 12AX7s in the SET amp this evening. Man this amp sounds good! The sound is so clear, the reverb so noticeable and the sustain is delicious. I'm also trying out the Sttafs on the amp as right now. They sound just fine, but I obviously have to turn the amp a fair bit louder to get the same level as the MA's. |
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Silver Member Username: HawkbillyNova Scotia Canada Post Number: 943 Registered: Jul-07 | 10 tube watts goes further than most think. Other than having to crank it a tad more, do you prefer the Sttaf's or the MA's with the amp David ? |
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Gold Member Username: DmitchellOttawa, Ontario Canada Post Number: 4003 Registered: Feb-07 | Hard to say Chris. I haven't had enough time time the Sttafs on the amp yet. I had really warmed up to the sound of the MA's on the amp. The Staffs are a little less resolving than the MA's it seems, but the Sttafs strength has always been their imaging. Surprisingly, the diminutive Sttafs kick out as much bass, if not more than the MA's. Now that I thrown a tube upgrade into the mix, it's really hard to compare. |
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Gold Member Username: T_bomb25Aurora, Colorado United States Post Number: 2225 Registered: Jun-05 | I heard all the Grant Fidelity amps at the RMAF,he is pretty expensive on his rebadged Yaqin's you can actually get them for about 3 times less,on the plus side i really liked the 300b amp,very different from the mushy sound of the older 300b's which is why i prefer single ended pentode amps,and preferrably ran in ultralinear,their much more capable with inefficient speakers than 300b's with outstanding bass. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 15001 Registered: May-04 | . Maybe I'm not understanding what you're trying to say, TW, but I've never seen anyone trying to run a single ended amp in UltraLinear operation and there would be no advantages I can see from doing so. Do you have an example of someone claiming they can do this? . |
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Gold Member Username: T_bomb25Aurora, Colorado United States Post Number: 2227 Registered: Jun-05 | Yeah Jan its a new concept,the most popular amp doing this is the MiniWatt N3 and the old MiniWatt which i have both,also the Teconaudio 34i,i have a friend that has 1,and go back and forth between them all the time.Another that im interrested in is Sunaudio has a KT-88 based single ended ultralinear amp,and Eddie Vaughn has the Carina which can be run in triode or ultralinear,its a el84 based amp like the MiniWatt.Ultra linear is much better in the bass,and better at driving tough loads better dynamics,a cleaner sound,we have a another guy that has single ended El84,EL34,and 300b triode designs,and the old MiniWatt stomped the bejesus out of them in bass and dynamics,and the new N3 is much better than the old 1,single ended pentode ultralinear is the way to go. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 15002 Registered: May-04 | . How about some links? I see no reason for this since UltraLinear was meant to provide the benefits of triode sound in a pentode tube. It had nothing to do with single ended vs push/pull. " ... the Carina which can be run in triode or ultralinear ... " Are you saying the single ended amps are run in UltraLinear while also running in se mode? NO push/pull here? Or, are you saying you can switch between (pentode wired as a) triode (in push/pull) operation and (pentode) UltraLinear (push/pull) operation. The former, I've never seen and makes no sense to me. The latter has been around for several years. PrimaLuna has been using this design for almost a decade. I don't believe I've ever heard of anyone claiming they can switch between se and pp without totally rewiring the amp. BTW, my limited experience with se pentodes is not as exciting as your's has apparently been. I saw no reason in the experiment other than pentodes are cheaper to buy than most triode output tubes. . |
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Gold Member Username: T_bomb25Aurora, Colorado United States Post Number: 2228 Registered: Jun-05 | Yes,single ended ultra linear,The Prima Luna's,Cayins,Melody ect. are all push pull designs,not single ended,same friend that has the 34i has the eupropean Cayin class A 70t and the and euro VPI 100,both designs are very good,and the Prima Luna's are built in the same factory as the Cayins which infact is their factory.Designs using ultralinear single ended pentode tubes 6bq,el84,e34,kt88 ect. are starting to pop up as of late,positive feedback,6moons,and enjoy the music have all reviewed the old MiniWatt,and Stereophile is gonna review the new N3.And yes my experiance with single ended pentodes run in triode are not very exciting to me either Jan,except for el84's,6v6,6bq's have consistently sounded good to me,EL34,KT88,6L6 less impressive except for Decware and Wright Audio and a few others,but single ended run in ultralinear is a all new level.Their is no 300b,845,or 2A3 i would take over a single ended pentode ultralinear amp,check those online mags for the reviews on the MiniWatt,their is also a review in Affordable Audio on the Teconaudio 34i. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 15890 Registered: May-04 | . Before tubes ... http://www.douglas-self.com/MUSEUM/COMMS/mechamp/mechamp.htm http://www.douglas-self.com/MUSEUM/COMMS/trumechamp/trumechamp.htm . |
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Gold Member Username: HawkbillyNova Scotia Canada Post Number: 1233 Registered: Jul-07 | Thanks Jan. interesting stuff. |
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Gold Member Username: John_aLondonU.K. Post Number: 4854 Registered: Dec-03 | Seconded! |
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Silver Member Username: EzntnGreeneville, TN Post Number: 203 Registered: Apr-09 | Afternoon folks !! Cary SLI-80 cooked another tube this morning. S6550 went nuclear when I turned the amp on. Glowed, bad static and that was the end of the left channel. Just ordered a new set of four Tung Sol 6550's from Upscale Audio which will likely be delivered late this week. Amp came with KT-88's One tube crapped out & I ordered a set of the Svetlana S-6550's shortly after I purchased the amp. Now, once again I am out one tube. I retained the KT-88's when installing the new 6550's. Here's my question: As the amp's layout is symetrical, can I install KT-88's in the inboard locations and run 6550's on the outboard location until I get the new Tung Sols? No doubt, I'd have to readjust bias after doing the switch, but would it hurt the amp to do so? In my logic, I don't see this causing a problem. Just curious if anybody else has rolled tubes in this manner? |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 16123 Registered: May-04 | . KT88's and 6550's are considered equivalent tubes. You should be able to run them together without damaging the amp as long as you can readjust bias for each tube. I would run them in pairs on one channel each rather than using one tube type for each half of each channel. If the tubes are failing in a similar channel, or particularly in a similar location in the amp, you might want to have the amp checked. While tubes do eventually fail over time, glowing tubes suggests a bad component within the amp. . |
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Silver Member Username: EzntnGreeneville, TN Post Number: 204 Registered: Apr-09 | Thaks for the advice Jan. I should point out, I leave the amp on almost continuously, similar to some fellow I know in Dallas, tho his Macs pump out a few more watts than I am capable of generating. It was shut off Sat night, turned on this AM, thats when the top of the tube took on an eerie, expensive glow prior to giving up the ghost. I'll install the KT 88's on the left bank and see what happens. |
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