[HAM] M3 Amp voltages and glowing 6V6 (long)

[Charles Buckingham]

Please forgive me if I'm not clear in this post.  I'm working on half a 
coffee.

O.k.  M3 Amp (PM speaker version) with blown power transformer and dead 
rectifier:

Replaced all electrolytic and paper capacitors.  Checked resistors to 
see if still in spec(ok).  Replaced power transformer (with transformer 
from FC speaker version). Replaced dead rectifier.   Checked chassis for 
AC leakage (ok).  Added 1-1/2 slow-blow fuse and 3 prong plug (after 
thoroughly reading the safety information and potential risks in the 
archives).

I didn't have a "complete" organ around to test the amp, so I connected 
an M3 generator, upper manual and an 8 ohm speaker to the amp on a 
workbench and fired it up. 

It worked.  And it sounds great (to me).

Here's where I'm a little vague:  I know the transformer from the FC amp 
has slightly higher voltages than the one from the PM amp.  I know that 
this isn't an issue when converting an FC amp to PM specs and that tubes 
have wide operating values (provided the maximums are not exceeded). The 
measured DC voltages in the "rebuilt" amp are much higher than I 
expected.  At the extreme, what is listed as 320v on the schematic is 
reading as 370v.  At the plates of the output tubes, the "305v" is 
reading 354v (V6) and 360v (V5) respectively. According to the tube 
specs, design maximum for the 6V6 is 350v (oops!).

Another issue is that after a few minutes there was a small red spot 
glowing on one of the plates of the output tubes.  Normally I understand 
this to be a bias issue so I checked the "-19v" going to the grids. It 
was measuring -22v.  Checking the characteristics graph this corresponds 
roughly to 20mA of plate current.  Not what I'd expect to cause a cherry 
spot. Swapping the two output tubes with each other showed that the 
glowing stayed with the one tube.  Looking on-line I found reference 
(from an article on tube biasing article by Lord Valve) that this is 
common in NOS 6V6's and is not generally an issue.  So, is this a "red 
herring" (forgive the pun, or not).

I also checked the voltage across the 30 ohm resistor at the front end 
of the power supply and read 4.16v.  The resistor was in spec, so this 
corresponds to a current draw of 139mA.  The schematic reads 140.  My 
gut tells me (and my brain too) that nothing is about to melt down.

So, do I have a "normally" working M3 amp, or a Frankenstein disaster 
about to run amok?

All my tube books are still in the boxes I used to move them in a few 
months ago.  Yeah, I'm rusty. 

Any advice or insight?

Better safe than sorry and off to get another coffee,

Many thanks,

Charles