Just installed an Electro Harmonix 12AT 7 from the Tube Store (Great service, BTW), replacing the 12AX7 in the preamp of my '69 Sceptre. This was prompted by comments by Joe Naylor of Reverend that this swap would produce a tweedier sound in their new Hellhound amp.
I used it to replace a JJ AX ( the new "S," low noise model). Decided to try the EH due to hype, forum chat, and use of EH by Reverend.
Results:
-- Slightly lower gain (Duuuuh!)
-- Better sparkle and chime. (Pleasant surprise, I feared worse.)
-- No change in noise, or maybe even lower noise.
-- Amp no longer "motorboats" at any output.
-- Volume and tone controls seem to have a wider range, less "all or nothing."
-- Amp sounds less "hard" and much deeper or spongier. Still has great growl when pushed.
The tube IS microphonic - just tapping the amp makes it "ping." But there is NO feedback or run away at any volume - right up there to unspeakably loud.
Bottom line, I think the amp sounds much better. I'm leaving it in, but I may buy a JJ AT as a spare.
Interesting experiment was the most conventional wisdom is to try it increase the gain of old Sunns so that they will overdrive better. Some maintain that this mod will elicit more output tube overdrive. Whatever the real truth, I like the results. Comments from the tech gallery appreciated.
YMMV
