heater to cathode voltages

[tubeswell]

I recall somebody here recently said that the Vibroverb style CF stage in the LFO of my modified tweed bassman build would be fine with heaters at ground potential, but in my recent build (now that I can turn the vol up without blocking distortion thanks to output tube grid stoppers) I get this intermittent weird oscillation with pops and crackles. At the moment the heaters are about 40V.

Just in case it might be the heaters wrecking havoc with the cathodes, the cathode voltages on the CF stages are; 159 (Reverb bypass - 12 AX7), 183 (DC pair follower - 12AX7), and 213 (LFO follower). Should I squeak the heaters up to 80V? (Can 6L6GC take 80V heater elevation?)

[Steve Conner]

Try a different tube in the various CF positions and see if the symptoms change. Also, is your elevated heater line bypassed to ground by a capacitor? Signals can feed through it if it's not, causing instability.