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In Reply to: RE: can i sub a 12ay7 for 12ax7? posted by DAK on August 12, 2015 at 19:51:44
Cont: You can get a little of the gain by using a 5751. I like them in positions that use 12AX7 as stock. Next with even less gain are the 12AT7s, but I don't use the 12AT7s pin out matches but they differ electrically
Steve
Follow Ups:
Thank you and I have already tried them. But, not really much difference that one can notice. I think I need to tweak the circuit. cheers, Dak
Funny that you should ask about which tube substitutions you can use instead of 12ax7s.
I think I brought this up a little while ago here, but I never got around to reporting how I made
out in my search !
I had switched to using a pair of 5751s on something that Tyll H. had mentioned about the HP amp I'm using (Fosgate Sig. Tube Amp). I want to say that the amp doesn't sound quite
as "Tubey" (placing an envelope of "air" around players that separates them from the entire
acoustic of recording) with the 5751s in place & the middle frequencies appear a bit more dimensional to myself. It was closer to what I'm looking for,but it really didn't give me much more volume headroom.
On one of the tube website there is a comparison of the gain differences between tubes that
often used as substitutes for 12ax7. If you assign a gain structure of 100 to the 12ax7 the
5751s are comparatively only a 70 . The tube that looked interesting to me was the 12ay7 which is a 45 on this chart (which looked very promising;but I wasn't sure would even work in the circuit)
Long story / short , I bought a pair of Electro Harmonix 12ay7 (for a bit under $50) that are
working even a bit better for me than the 5751. While I like these tubes more than the 5751
& quite a bit more than the 12ax7, my useable volume problem is still limited. The problem
is this HP amp really doesn't need to see the 2volt output of my Metrum Hex DAC to drive my Senn HD800s without overdriving very quickly by the time I set the vol. to 8 or 9 o' clock!
Someone suggested (Yesterday, I believe) that I try some Rothwell Inline Attentuators . These look very promising to me. I honestly don't think that changing to a different preamp
tube type in a circuit will do much to change how much volume control "wiggle room" that
much if you're having a problem running out of volume too quickly . Think of the tubes as
tone generators ,not gain generators.
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