Pro Audio Asylum

Posted by freddyi (A) on October 04, 2004 at 19:30:41

In Reply to: Fender Twin Reverb -65 reissue posted by Stewen on October 01, 2004 at 13:34:34:

hi Stewen - be better off to leave output transformer alone - Ultralinear (with its higher bias) requires more drive capability than running pentode/tetrode plus a change may oscillate and create a nightmare

FWIW - up front, in the first preamp section, you might be able to go to lower mu tube - maybe 12AT7 to drop gain a bit and get it "cleaner" - check disipation in tube and associated plate resistor plus bias as seen as voltage crpo across that tube's cathode resistore - guitar tube guys on a number of forums should be able to tell you if 12AT7 will plug and play fine - I've done this on one Traynot

re:toroids - in a reverse situation - the loudest space coupled hum I've heard came from a toroid mains' transformer's high Q recitfied "buzzy" field coupled into an EI core output - this could be heard 20 feet away with output trasformer feeding a ~99db sensitive speaker - without any amplifier circuit whatsoever.

best,
Freddy