Specific instruction/changes for wiring a 6CG7/6FQ7 in place of 12AU7, Please

[tvr2500m]

I went and bought a second Crack. Yep, I did it. I am enjoying my stock Crack 1.1 + Speedball C4S enormously. It's a tidy, well-shaken-down build and it sounds great. I'd like to leave it in its current state undisturbed, so I bought a second one to enjoy some modest hot rodding. I have a plan. The usual'ish stuff people do. I'm not going into this assuming to better better circuit executions, like a Crackatwoa or Mainline, with fancier bits.

One of things I'd like to do is experiment with the 6CG7/6FQ7. Having had Conrad-Johnson amps forever, I have a big stock of these. I also have a lot of nice 6SN7s, but considering to try the 6CG7 first.

Both 12AU7 and 6CG7 use very similar basing. It looks like just the heaters need to be wired differently. I would appreciate someone describing what has to happen to wire the 9-pin 12AU7 socket to accept a 6CG7.

Thanks!

[Paul Birkeland]

On the 12AU7, the heater supply feeds pin 9 and pins 4+5 tied together.

On the 6CG7, the heater supply needs to feed just pins 4 and 5.  Pin 9 should be grounded.

[tvr2500m]

From the 12AU7 socket wiring, unsolder/remove the heater supply wiring tying together pins 4 and 5, and also unsolder/remove the heater supply wire going to pin 9 (the heater center tap). For the 6CG7 wiring, connect those two heater supply wires each directly to pins 4 and 5. Then, ground pin 9 (which is the shield between the triode sections of the 6CG7).

Is that it?

How best to ground pin 9?

Thanks.

[Paul Birkeland]

Yes, that's it.  Terminal 3 is a ground.

[tvr2500m]

Roger that. Easy enough.

Thanks.