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

@oldtecg05
 Whose thread is this?

I thought it was mine. I dont mind a bit of controversy as long as its Gentlemanly and with some sense of humor. Its the sense humor that I find lacking.

Here is a great example of what I consider the proper use of 6SN7 and 6SL7. Note all the preamp and phase inverter are SLs. Interestingly the SN is used as a push pull output tube... So cool. Its worth reading some of the thread.

https://music-electronics-forum.com/showthread.php?t=16661

This is a golden nugget of wisdom;

(In their book "Control Design And Simulation", Jack Golten and Andy Verwer discuss (in chapter two) with regard to applying mathematical models to the real world: "...mathematical models invariably involve simplification. Assumptions concerning operation are made, small effects are neglected and idealized relationships are assumed." 

Ralph-you should never have entered this thread. You tried to kill the OP with kindness and camaraderie, and he spit on you every chance he got. I think most of us reading through this thread can see the OP for what he is; entrenched in the remote past and bitter. His hubris is out of bounds. I have been around long enough to suspect that there must be something else going on in the OP’s life that is causing him to behave so poorly.

What causes a designer to choose a certain tube type for an audio circuit? Is the circuit designed around a specific tube, or is the best tube type found for the circuit that’s been/being designed? I know there are different electrical properties (I’m not an EE, so that is my untrained understanding), but does one choose the tube primarily for its electrical ability, sound, reliability, or some combination?

What causes a designer to choose a certain tube type for an audio circuit? Is the circuit designed around a specific tube, or is the best tube type found for the circuit that’s been/being designed? I know there are different electrical properties (I’m not an EE, so that is my untrained understanding), but does one choose the tube primarily for its electrical ability, sound, reliability, or some combination?

I know you would prefer that RM or RK answer this but I have something I can add. I asked this question of ARC's techs (I don't recall which one I spoke to) about their current penchant for designing power amps around the Tungsol KT150 and before that, the KT120. In ARC's case, I was told that they did the former-designed their amps around these tubes. If you happened to follow the history of the Ref series of amps, this is fairly obvious. The KT120 hit the market and the then-current Ref series of power amps were shipping with KT88's. They were able to handle the increased transformer demands presented by the KT120, but just barely. ARC reacted by beefing up their transformers to accommodate the KT120. Then the KT150 came out and this time, ARC was ahead of the curve rather than behind it-it seems they were got their hands on the KT150 before it was released to the public and were able to come to market with their Ref 75SE and Ref 150SE with KT150's installed. This was true of the GS "Galileo" Series as well. The tech I talked to told me that they felt the KT150 was far more linear and "accurate" than all of the predecessor power tubes, and also more durable. Too bad (for me) they are also significantly more expensive. That said, I used an ARC VS110 for about ten years and went through about six sets of various KT88's, 6550's, and even tried KT120's. I know, without a doubt, that I am getting far superior sound with my present amp, the Ref 150SE. The VS110 had a sweet slightly euphonious sound. Bass was good, but nowhere close to the solid slam I get with the Ref 150SE. The treble is far less grainy with my present amp as well.