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In Reply to: RE: Just the left channel, right? posted by David Smith on October 13, 2014 at 09:28:19
SE is sort of implemented experimentally. Although, the specs do look pretty good in testing. It's done by not driving the grid of one side of the amp. The undriven side is pentode connected to increase its impedance and is used to balance the DCI in the output transformers.
The SE modes on this amp take a back seat to the push-pull modes, which are the principal modes the amp was optimized for. This sort of hybrid SE is not exactly optimal, but still results in 6 watts in Triode SE mode with 1.4% THD with *no feedback applied* and will obviously get much lower with feedback (up to 14db in this mode).
Again the amp is really designed to be push-pull optimized, but the three SE modes give rise to a lot of experimentation.
Follow Ups:
I don't want to nit pick, but if I were spending that much time and money on 6 watts, I would opt for some very nice gapped SE silver custom transformers and a single output tube like a 75TL.
Please read the circuit description. As I said earlier, this thing has 6 modes of operation, only 3 of them SE, and PP was the primary design objective.
I take it you are after a steam punk show-off object rather than sound?
I gotta ask you this - do you actually get anything out of crapping on other people's work? Just curious. First off, this project started in '97 before "steampunk" was a word. Secondly, this amplifier has VERY good specs in all modes of operation, even the silly ones. Lastly, this project was SPICE modeled, tweaked, and is being built with the best possible components available. I got help from one of the best analog designers I've ever met, and every single aspect of this amp has been thought out to an extreme.
If you're not interested in giving real critique, or learning from anything that I show here, then fine. I have no problem with that. Why some people feel the need to troll an otherwise productive forum baffles me endlessly. Perhaps if you can shed some light on that, you will have contributed something after all.
"I also have 6 modes of operation, they are called 6 different amps"
Can I be YOU for a day?
You have not provided any circuit diagrams or details and have not completed the amp in 17 years of work. I have given you fair criticism: A purpose built amp will sound better if your goal is good sound. We here usually don't debate theoretical Spice specs.
A lot of people build tube amps because they look cool. Yours, if completed, will definitely look cool. Unfortunately, due to the laws of physics, a push-pull output transformer current balanced into supporting SE will not perform up to the standards of a good SE output transformer. I can only guess what your designer is trying to do.
"You have not provided any circuit diagrams or details and have not completed the amp in 17 years of work."
No, I haven't provided any circuit diagrams, except to those who asked via PM. I am not the sole copyright holder of the schematic, it is shared with the person who did all the heavy lifting on the design end. I have not yet obtained permission to post it publicly. If anyone is *truly* interested, I'll be happy to email it to them privately, with the promise that they won't post it or use it commercially.
As to the time it's taking me to build the amp, well, life is complicated. Things take time. Would you prefer it if I had just slapped everything together into a Hammond box in a couple weeks? No, you wouldn't because then you couldn't chortle madly as you accuse me of being some sort of steampunk hipster like you did a few posts ago.
"A purpose built amp will sound better if your goal is good sound. We here usually don't debate theoretical Spice specs."
This amp IS purpose built for push-pull operation, and optimized for it. The amp performs very well on the bench as a test jig, as well as in the SPICE models, which nobody is debating, since I never posted them.
"A lot of people build tube amps because they look cool. Yours, if completed, will definitely look cool."
Well, thanks I suppose. Is that an actual compliment? No, you're just damning me with faint praise I suspect.
"Unfortunately, due to the laws of physics, a push-pull output transformer current balanced into supporting SE will not perform up to the standards of a good SE output transformer."
Gee, I suppose it's really a good thing that I OPTIMIZED THE AMP FOR PUSH-PULL USAGE.
"I can only guess what your designer is trying to do."
Well, maybe if you simply asked, I could explain it all, if you were actually interested in an explanation rather than trying to boost your own ego by crapping on other people's work.
That designer, BTW, was none other than Steve Bench. You can guess all you want, because you and me combined couldn't even begin to touch those kind of engineering chops. It's a checkers versus chess scenario, I'm afraid. Luckily, the schematic came with a very well articulated circuit description, test results, distortion measurements, etc. and feeble minds like mine can then grasp the rather incredible circuit that was crafted.
Obviously my amp bores you, right? You've stated that my approach is inherently flawed, and doomed. Ok, I heard you. That's the only point you have, and you've made it. If you keep coming back here to this thread, I can only assume it is because you want to troll me. Until you make some real observations, I'm just going to ignore you.
"a push-pull output transformer current balanced into supporting SE will not perform up to the standards of a good SE output transformer."
Why is that? Any reason other than loss of efficiency?
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Buy Chinese. Bury freedom.
I have found that a big part of the SE sound is the output transformer. A very good air gapped SE output transformer has as much to do with the SE sound as does the tube type used; they overload gently and musically. You can balance the currents in a push pull transformer with a dummy load, but that circuit will have a penalty as the current source is in the signal path and it will be a challenge to keep the currents balanced as the tube(s) ages leading to saturation distortion at all output levels.
Because you can do something does not always make it the best solution.
Gee, I suppose it's a good thing that my amp was optimized for push-pull. Maybe if I say that a third time, you'll drop your obsession with the fact that the amp offers admittedly non-optimal SE configurations as a bonus. I don't know what to tell you, you're suggesting that I basically go back to the drawing board and reconfigure my amp to be something that was not intended. This amp is purpose built for push-pull (for the fourth time) and offers SE as an aside. I never even came close to claiming that this was anywhere near the best possible SE amplifier. Frankly, I'm not even a big fan of SE, which is why those modes take a back seat, and why Cit II iron was chosen.
I am glad you are enjoying the amp. I must have tuned out half way through your opening 7 posts, sorry for the confusion.
People swear by his SE amps. And the SE 45 amp I heard in his basement was outstanding. He used OPTs from vintage Push Pull Webster Organ amps. I neve could get a straight answer as to why they sounded good . I never would have used those OPTs but they were actually fine. I am still puzzled how he used those OPTs for a wider variety of amps.
Edits: 10/14/14
Most likely, these transformers had enough of a natural gap to support the low current from the 45.
way back in the beginning of the us se craze sp did a article on a budget 45 amp. And I think it mentioned using a big pair pp trans as 40 ma wasn't enough to saturate them badly. There was something about webster outputs. I have read many times that they are extremely musical outputs. paper insulation and 50 years of core and wire break in might be the secret. I just bought a sansui amp for the outputs. I payed more then it would of cost me to have silk wind me a new pair. I think the sansui outputs are worth the money. And don't worry I wont break it up if it is restorable.I was looking at buying a vintage dagger a few years ago and I also read that you have to look out for flat areas in the blade as some after 50 years the metal actually breaks down. Which also makes me wonder what affects that time has on vintage transformer cores. Good or bad.
Edits: 10/19/14
nice audiophile amp
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