[USER=56916]@scott2000[/USER] you're right. Drawing the circuit is very helpful. I've done this for the "amplifier" section by hand. I mean the driver tube (ECC83) and the following final tube (ECC82) with the output transformer.
But it's quick-made by hand and I don't dare to upload it here, it's really awful 
I'll try to "edit" the existing schematic of LCA-2B (amp section) so MEC1A's one doesn't seem so ugly...
P.S. The wiper of the "Output gain" potentiometer goes (via a 470nF) to the driver ECC83 (pin2, grid) and the AC mV on the wiper is stable. That means to me that the issue is in the amplifier section (including of course ECC82, output transformer AND ECC83 with all the passive components around them).
By the way, here are the "typical characteristics" from Philips' ECC82 datasheet
[ATTACH]98999[/ATTACH]
Below the "typical characteristics", there are "operating characteristics" of the tube as "af amplifier" with power supply voltages 100 - 400VDC. But all projects of course, have a resistance in series between power supply and the anode (47k - 220k in the datasheet). That's normal.
I attach the Philips ECC82 datasheet.
