Does anyone care to ask an amplifier designer a technical question? My door is open.

No one has said this yet, except Roger, in his response to my 1st question. If this isn't a form of advertising and exposure, and yes, to sell some amplifiers, I do not know what is. Awesome Roger ! Enjoy ! MrD.

Hello.
I am very slowly learning how power amplifiers work and have a hybrid car amp with low voltage 12ax7 tubes for the input signal that got hot and melted the plexiglass cover and some nearby hot glue. Do they normally get warm enough to cause these symptoms? It is a USamps Ax-Tu1000. They use what is called "vacuum tube current sync drive" and cannot find any info or a more universal name regarding it. I purchased it used and the previous owner claims his speakers got ruined but find it hard to believe.
Thank You.

This is not in a bad way. " First I'm not using this post to sell amplifiers, that is up to you. " Exposure, soft selling, putting the puppy in my arms. Genius ! All good. Love the thread ! Enjoy ! MrD.

@unrecievedogma

Hi ramtubes,thank you for that and here’s a followup. If triodes are low impedance and OTLs like high impedance, what was Jon doing then when he switched the OTLs to triode?i can tell you that the amps sound better after the conversion, and they are more stable too. The bias and the balance don’t drift anymore. Jon Specter made the conversion with some guidance from George Kaye of Moscode. Both formerly worked at NY Audiolabs.

Are we talking about NYAL Futterman? Perhaps I have missed something in this thread? Do you mean Jon Snyder?

This may help. Triodes are low impedance at the plate. The Futterman circuit doesnt care about that. Ive made some triode and some pentode. One gets more power with pentode and I can image they drift more in pentode. 

What a terrific thread!  Thank you Roger!

I hope you can answer a couple questions that have long baffled me about the sound of some amplifiers - in this case, using my own as example.

Earlier in the thread, you mentioned how the impedance interaction with a speaker is a significant factor in how one amp might sound different than another, depending on the design.

I've always understood (or not understood?) this to mean that if the amps performance varies with impedance swings presented by the speaker, you will start to get contoured sound around those impedance swings - e.g. more or less bass here, more or less highs there etc.  Like a tone control.

And if I have that right, and one is using an amp that is very susceptible to altering the signal based on the impedance character of a speaker, then the "tone control" variations ought to vary as you switch between speakers.  So one speaker may sound fairly neutral (if it doesn't present a tough impedance load with said amp), another may sound rolled off, another boosted in the bass, etc.

The thing is, in my subjective experience, the character of an amplifier (at least the ones I own) tends to seem more constant than that. 


So take my Conrad Johnson Premier 12 tube monoblocks - for reference, measurements here:

https://www.stereophile.com/content/conrad-johnson-premier-twelve-monoblock-amplifier-measurements


I have had a ton of speakers of varying designs - Quad 63s, big Thiel speakers, transmission line bass, reflex, sealed, tough impedance curves, easy ones....

And I've tried numerous amps, including some solid state (Harmon Kardon, Bryston 4BST, and others), and the thing is, the "character" I hear when I implement the CJ amps seems to remain constant: a slightly more rounded sound, that classic bit of "golden glow" in the upper mids/high frequencies,  rounded but taught bass, etc.  I just don't seem to hear the tonal variation I should think may happen.

An even worse example is my  Eico HF81 14W integrated.  I'm sure you know this infamous little "classic" amp.  It sure didn't seem to measure well:

https://www.stereophile.com/content/eico-hf-81-integrated-amplifier-measurements

And, if I understand the implications of those measurements at all, it would suggest the amp would be susceptible to sonic variation, as speaker loads vary.

And yet, the little guy just seems to "sound the same" no matter what speaker they drive: from easy to drive monitors I own, all the way to MBL radialstrahler 121 omnis (a brutal load), to even my big Thiel 3.7s.  They always have that same sound - a sort of lush, thickened, sparkly not "dark" sound, with a swollen bottom end that makes any speaker sound "bigger."  (My hunch had always been this was some "low damping factor" in the performance of the amp that gives it this character across speakers, but now you'll slap me upside the head for that).

So my questions are:

1. Why might I be perceiving that the amps have the same essential character even when used across a wide array of varying speaker loads?

2.  Even more confusing to me:  We are often told that the distortion signature of an amp tends to give it a sound.   But for the most part, this arises only when power is under high demand, clipping etc, correct?  If so, why do the amps seem to retain their specific character no matter what volume I play them at? 


I don't tend to listen loud.  Often topping at around 75 dB or so.  As I understand it, at least when I'm not listening to music with dramatic dynamics, most amps should essentially be cruising in terms of distortions.  So if they are not going in to the type of distortion that starts to distinguish amp distortion profiles, why do they still sound different even at lower volume levels? All those "tubey" characteristics seem to be there no matter the volume.


Now, of course a confounding variable here is listener bias.  But, if I'm hearing what I think I hear, I'd appreciate your unraveling my confusion.
Thanks!