Hot Rod Deville- New wattage?

[pdf64]

The standard published 12AT7 data for u / anode resistance / gm applies at anode currents of 3.7 or 10mA.
Whereas we use them at rather different operating conditions, far lower levels of anode current, with correspondingly lower gm https://frank.pocnet.net/sheets/093/1/12AT7.pdf

[Helmholtz]

The standard published 12AT7 data for u / anode resistance / gm applies at anode currents of 3.7 or 10mA.
Whereas we use them at rather different operating conditions, far lower levels of anode current, with correspondingly lower gm https://frank.pocnet.net/sheets/093/1/12AT7.pdf

Yes, all 3 essential triode parameters vary with plate current but are always related by Barkhausen's law stating that µ = gm * rp.
So a higher gm might be compensated by a lower rp. This typically happens with a 12AX7, which has a fairly constant µ over current.
Just saying that lower gm doesn't necessarily mean less gain, though it might be true for the 12AT7.
Datasheet charts and a little gain calculation will tell.

For gain reference I used the comparison chart you provided (I think it's from Hot Blue Plates) where all tubes use the same 1.5k cathode bias resistor.
With Kuehnel's LTPI calculator I varied the shared bias resistor between 470R and 820R but the difference is small.

[35L6]

I think he may have meant more output swing rather than gain . In my recent build I used a fairly typical LTP . 1M grid leak , 1k bias , 22k tail . I wasn't sure if I should use AX7 orAT7 . Reading online it seemed with one you have a gain of 20 and can input 1.5V and the other a gain of 10 and input of 3V . Seems the same so I got one of each and tried them . Got more swing from the AT7 but not by much . Both would drive the outputs to clipping . I would say either one is just fine . I didn't look at NFB so I may revisit this .

[Helmholtz]

Wow, seems R.Kuehnel is watching our thread!
Today I played with his calculator again and now I'm getting a gain of 16.8 with a 12AT7 (was 26 before). Pretty much what I expected.
So he must have corrected his tube model.
Thanks for that!

[pdf64]

Wow, seems R.Kuehnel is watching our thread!
Today I played with his calculator again and now I'm getting a gain of 16.8 with a 12AT7 (was 26 before). Pretty much what I expected.
So he must have corrected his tube model.
Thanks for that!

I sent an email to the ampbooks contact address, he responded that the calculator was using the 10mA characteristics, no mention that it would be fixed. So it's great that it has been, thanks!