I finally got around to trying these out in my Blues
Express, with a toggle switch to A/B between different
values... damn but it sounds nice!
 
    With a single pair of EL84's in push-pull I settled on
a 10k/1W resistor (7000 ohms x 1.3). For the cap I
tried a few different 1kv ceramic caps I had around and
2200pF sounded the best to my ears.
 
    So what effect does it have on the sound? It sort of
makes everything sound fuller... when you switch back
to no filter the sound just gets duller. I would have
thought that the conjunctive filter would have cut the
volume a little bit, but it makes the sound stronger! (Go
figure...      )
 
    In any case, run don't walk to the nearest parts store
if you don't already have a 2200pf/1kv ceramic cap and
try this out on your 2-EL84 amp. (Question: if you had
FOUR EL84's the recommended plate load resistance
would be 3500 ohms... right? So I guess that you would
use a 4k7 or 5k1 resistor... Might be a good idea to try
that out in my "tweedified" Peavey Classic 50!)
 
    I've included a copy of JaySG's post to refresh
everybody's memory.
 
--Enjoy!
 
Steve Ahola
 
P.S. I'll be trying a switchable local feedback loop on
the second stage of this amp next... .047uF/630v cap
and probably 22M and 44M resistances.

Q/
You place the resistor (1k 1W) followed by a 2n2 1kV
cap across the primary of the OT?? I have some 1kV
polypropylene 2n2 1kV so I might try it with those. 

A/
Yes they are wired in series.

A/
And I think your earlier post about the 32M pretty
much nailed it. I tried 40M and 20M, and found 30M
(er 32) worked out nicely. Thanks again.