I got a BK707 (i think that's what it is) pretty cheap and a guy in Seattle fixed it up for 100 bucks. That's all he does, refurb testers.
I can't speak for others, but when I try different tubes, I take voltage measurements (and apply Ohm's law) and make the necessary adjustments to components, primarily resistors, to get the tube operating in its linear range. I actually had to do that a lot even early on as I rarely used the 12xx7 family of tubes, and most schematics called for the 12xx7 family, and usually the 12ax7. What works good for the 12ax7 didn't always work so well with the tubes I substituted until I made adjustments, then I nearly always got equal or better results. A generalization I noticed is bigger plates sound better. When I tried the 6SN7, I was really surprised at how much better it sounds. And the lower gain didn't really seem to make that much diff, which I found interesting. Perhaps the greater transconductance compensates? The volume was reduced, but only slightly so.
Even if I'm trying different power tubes in a cathode-biased amp, I still take measurements. I put a 10-ohm resistor on every cathode regardless of design so I can monitor and match. I don't think you can make a valid conclusion if you don't give a particular tube a "fair deal" by optimizing the circuit for it to the best of your ability
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But in the case of a cathode- biased 6V6 or 6L6, how much adjustment do you think one is going to make? I can't recall having to even adjust the cathode resistor when trying a different tube in those cases. Not that I'm that big into tube-rolling. If I find a set of affordable tubes and they sound good, I'm happy. if another set of tubes falls into my lap, I might compare out of curiosity, like when I compared the legendary GE Double-D getter against the 6P3S-E, and the Russian tube was vastly superior.
Re-hashed or re-engineered?
To be entirely fair there isn’t anything in tube amplifier configuration that as not been tried before. It is all basic building blocks just put together in different combinations. So unless we get a totally new and novel component such as Peter Walkers unique output transformer configuration that is pritty much it, you will always see something of a désaveu with every circuit you look at...
But as Morcombe and Wise famously said to Andre Previn “I'm playing all the right notes—but not necessarily in the right order."
That is the secret of a truly great tube amplifier right there, all the right parts in the right order! That is the genius of re-engineering a circuit. Keeping the components to a minimum, keeping the signal path simple as possible, having a clean and stable power supply with a generous capacity for current and using carefully matched ( for the circuit) output transformers of the highest quality.
Re-harassed or re-engineered?
To be entirely fair there isn’t anything in tube amplifier configuration that as not been tried before. It is all basic building blocks just put together in different combinations. So unless we get a totally new and novel component such as Peter Walkers unique output transformer configuration that is pritty much it, you will always see something of a désaveu with every circuit you look at...
But as Morcombe and Wise famously said to Andre Previn “I'm playing all the right notes—but not necessarily in the right order."
That is the secret of a truly great tube amplifier right there, all the right parts in the right order! That is the genius of re-engineering a circuit. Keeping the components to a minimum, keeping the signal path simple as possible, having a clean and stable power supply with a generous capacity for current and using carefully matched ( for the circuit) output transformers of the highest quality.
This doesn't tell you the whole story by any means. The spec sheet for the 6V6 gives:
PO= 14W
THD= 3.5%
RL= 8K (P-2-P)
PP Class AB1
For the 6L6:
PO= 26.5W
THD= 2.0%
RL= 6K6 (P-2-P)
PP Class AB1
The distortion for the 6L6 is significantly lower. That doesn't mean it sounds better, since it doesn't. The 6L6 likes to make a lot of higher order harmonics, and running open loop, that sounds just plain nasty. The 6V6, however, makes mainly h3, and tends to sound "aggressive" or "edgy" running open loop, but you don't get that pentode nastiness.
Doesn't mean 6L6s (or the 807 version) can't sound good, it's just that you have to work at it a bit more. 6L6s need some extra assistance from lNFB as well as gNFB.
Another type that acts much like a 6V6 is the 6BQ6GA (GTB) -- a TV horizontal deflection type. It's almost all h3, and very little of that anyway, especially if you bust the PD spec and bias hot. You can get away with that because the 6BQ6 is rated very conservatively, given its intended purpose; the spec sheet makes no mention of audio final use at all. Both the 6V6 and 6BQ6 just require some gNFB to take the edge off, and to help with the damping factor to tighten up the bass.
If you see "audiophile tube", better hold tight onto your wallet because you're gonna get $ROOKED. Lots of types I'd like to try, but they're way too PRI$EY.
My thinking exactly. There are a lot of audiophile sleepers out there, both large signal and small signal, types. Start talking 'em up, and the price goes up. Oh well...
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I was recently in discussion to purchase a third-hand KT-77 based Empire Electron amplifier that Steve White produced. Although I have not heard the amplifier Steve lives just down the road from me and I really like supporting local talent.
The seller, a vintage audio store, said he enjoyed the amp but could not have it in his home as his young daughter was attracted to the glowing tubes and would eventually burn herself if not removed. At that point I made an offer, which was accepted, and I was mostly happy with the pending purchase. I say "mostly" as I still had to do some research of the unit to see if it would integrate perfectly into my system before laying out a fair amount of cash.
This lead me into internet searches which lead me here. I am all about the betterment of technology through discussion and scientific analysis. I like seeing a detail paper to give me the general parameters of performance and compatibilty. None were found anywhere.
After reading all 69 pages of this thread and additional pages on the "The Teacher" I have decided that I had to call off the purchase of the amplifier. There is no documentation to be found anywhere, the builder would not supply any data to the forum membership and, personally, I did not like the builders ego, building practices, lack of technical knowledge and attitude. If, after purchase, I found that the amplifier was not to my taste and tried to resell it the prospective buyer could always run an internet search and come to the same conclusions I did. I didn't want to purchase a device only to move it along at a loss.
I'll spend my cash elsewhere. I want solid value for my money, not pipedreams.
The seller, a vintage audio store, said he enjoyed the amp but could not have it in his home as his young daughter was attracted to the glowing tubes and would eventually burn herself if not removed. At that point I made an offer, which was accepted, and I was mostly happy with the pending purchase. I say "mostly" as I still had to do some research of the unit to see if it would integrate perfectly into my system before laying out a fair amount of cash.
This lead me into internet searches which lead me here. I am all about the betterment of technology through discussion and scientific analysis. I like seeing a detail paper to give me the general parameters of performance and compatibilty. None were found anywhere.
After reading all 69 pages of this thread and additional pages on the "The Teacher" I have decided that I had to call off the purchase of the amplifier. There is no documentation to be found anywhere, the builder would not supply any data to the forum membership and, personally, I did not like the builders ego, building practices, lack of technical knowledge and attitude. If, after purchase, I found that the amplifier was not to my taste and tried to resell it the prospective buyer could always run an internet search and come to the same conclusions I did. I didn't want to purchase a device only to move it along at a loss.
I'll spend my cash elsewhere. I want solid value for my money, not pipedreams.
in his head?
The tubes aren't the only thing with a vacuum. Oh, please, enlighten us, what is this mythical "tuning" that goes on? This sounds vaguely reminiscent of the accolades heaped on the now deceased Mr. Fischer of the Trainwreck amp fame. Supposedly his (extremely unsophisticated circuitry) only "worked' because he "tuned" each amp. Sounds like someone is playing to the "magic capacitor" crowd.
The tubes aren't the only thing with a vacuum. Oh, please, enlighten us, what is this mythical "tuning" that goes on? This sounds vaguely reminiscent of the accolades heaped on the now deceased Mr. Fischer of the Trainwreck amp fame. Supposedly his (extremely unsophisticated circuitry) only "worked' because he "tuned" each amp. Sounds like someone is playing to the "magic capacitor" crowd.
I exumed and ressurected the thread as a Thank You to the membership for not only me (it's only money) but maybe for a little girl and her family. As I'll soon be seeing the present owner of the Empire amplifier I'll ask him to unplug it as it may be a fire hazard. Hopefully Steve has recalled it for the grounding issue and there is nothing to worry about now.
Yes, proper grounding is essential for safety. I guess I had forgotten or not remembered that particular issue brought up in this thread. Thanks for the heads up HiLift.
tube rolling is never about tubes......
it is about the excitement these guys think they get when changing tubes......it is all in the head.....if you convince yourself that tube rolling works for you, then it will....
me. i just listen to the music.....i am a tube head, i like the sound of tubes....😀
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