e80cc in center position on st-70

Can this tube be used in this position

I have the 12au7 version of your st70 amp. I have several e80cc tubes that I used in another preamp without any issues. I use 3 12au7's and the amp works fine. I plugged the e80cc's into the middle position and got a crackling sound out of the right channel. It does the same thing with all 3 e80cc's I tried. Bias remains stable. Any ideas.

Mmmh... if the problem arises only on one channel, with any e80cc tubes you tried, I would check the tube socket contacts tension. The e80cc could have smaller pins than 12au7. Just my 2¢...
Best regards,
Danskman

I will check it. I can use the e80ccs on both the outside positions without a problem its only when I insert one of them in the center.

Yes, that's why I tought about the socket, especially the middle one.

the E80CC is the same as a 6085 tube, it has about 50% more gain than a 12AU7, and more important, it uses double the filament current.

I am preparing to build my new VTA-70 board and would like to use E80CC in the center position. I have the upgraded Power transformer, so the additional heater requirements should not be an issue.

My question is what component values should be changed from the standard schematic to optimize the operating point for the E80CC.  I wondered if other VTA experts have experimented and came to conclusions since this very old thread started.

I would try the following changes to use the E80CC tube in the center position only
R5 & 6 150 ohm
R9 & 10 1.5K
R11 & 12 47K
R13 & 14 68K

Will try those values and send followup if I have any comments.