[gurevise]

I'm concern about EQ stability in Cornet.
I look to me that the output/internal impedance of tubes play major role in both EQ's. As tubes age and drift, this will change EQ time constants.
I would think that resistors in RC circuits should be much higher values then output/internal tube impedances to swamp all tube's drifts.
Any comments?

Thanks
Sergey

[hagtech]

Yeah, EQ will drift as tubes age, bass increases and treble softens.  Not that much.  Maybe 1dB to 2dB tops.  Without cathode bypassing, the tube resistance is way higher than you think, leaving most of the EQ to be defined by set resistors.

Most designers run very high series resistors after the gain stages to better "define" the EQ resistances.  The drawback is that it adds a lot of noise.  Last thing you need on your sensitive front end is an extra 300k noise generator.  I don't do that.  I went the opposite direction in the Trumpet and Cornet.  This also has the side effect of getting the tube more involved in the circuit, which makes tube differences quite noticable when rolling.

But hey, to each their own.  If you want to redesign the EQ section, by all means, go ahead.  I have placed resistor locations for such already on the board.  

jh