[Harp-L] Re: amplification question - unbalanced PI

[Jim Rossen <jimjimdr@xxxxxxxxx>]

I found my JJ ECC832 and tried it as a PI in two amps.

First was a 1968 Super Reverb with BF PI conversion, otherwise stock
circuit, squashy 5R4 rectifier and Weber Sig10A speakers with H dust
cap x 4, Shure CM element mic.   I compared it to 12AY7 and 12AU7
tubes in the PI. With the 12AY7, the amp sounds pretty good and has a
semi-clean mid scooped sound at moderate volume.  It distorts
pleasantly at max volume and gained some mids.  With the 832 the amp
had more texture and distortion at all volumes.  This distortion was
pleasant sounding and the amp was more fun to play.  The feedback
threshold was higher.  Overall I preferred the SR with the 832.

Second amp was a carefully harp tweaked one-off tweed 5F6A Bassman
circuit played into the SR cab, also with a 12AY7 PI and  CM mic.
This amp sounds about perrrrrrrrrrfect to me as is.  The 832 added
distortion with tone that I liked less well than with the 12AY7, and
did not add volume.  I like the Bassman better with the 12AY7.

Based on this experience, the effect of the 832 depends on the amp.
Seems like it is worth a try in Fender BF/SF circuits that use a long
tailed pair PI.

Jim R