So...... The difference between the ECC83 I took out and the ECC823 I put in was that the ECC83 I took out actually
worked!
They must have sent me a dud!
With the 823 installed I could maybe get the 40CR as loud as a Marshall MS-2 Micro Amp, on any channel.
Except with plenty of hiss and no gain.
Reinstalled the 83 and normal service is resumed.
I tried the 823 once more to eliminate 'seating' issues, but no-go.
Back in with the 83!
But, at least I got to do the 40CR re-bias.
It had held pretty steady in the year or so since I first biased it to 35mV.
The right was still at 35mV and the left had only drifted down to 34mV.
Now, to pen a letter of complaint.