Never heard of subbing a 12at7. Run the by AR. I agree with Dekay. Although it is not recommended to substitute a 12AT7 for a 12AX7 a is simply a special industrial type of 12AX7 with lower gain and a slightly higher heater current.
Amplification factor of the 12AX7 is where the is Hi TJ: A couple thoughts. Distortion in the circuit is actually considered a good thing. Anyway, to my knowledge the 12AT7 has lower plate resistance and higher transconductance than the 12AX7.
I took a quick look at on-line tube data and they are not mentioned as substitutes on the couple sites I visited. You can look here for the plate curves of two makes of the two tubes. They are quite different. In any event, I think you would be changing most of the operating points and likely the sound of your pre in order to change the gain for one source. This might cause more trouble than it solves. Do you like the sound of the pre now? Is the gain about right for your vinyl now?
You generally want as little gain as possible and still be adequate I do not know anything about your pre. If you like the sound of it now and the gain in your phono is about right I would maybe attack the gain problem for the cdp alone instead of introducing all sorts of unnecessary changes to the entire system.
My guess is that the most direct way to solve a gain problem with a cdp would be to add some resistance in that individual circuit. Maybe as simple as adding a resistance to the interconnect or the OP stage of the cdp. Mcgjohn was willing to share their experience with exchanging an AX7 with an AT7, which was not my question, but the answer was interesting and offered in an informative way. It's unfortunate others here can not follow the same quality of reply.
Bill Ferris and jgscisum like this. Bill Ferris and KA1J like this. The other thing I will mention on the MC, is to replace that uf 3V electrolytic cap in the global feedback loop with a Nichicon audio grade Bipolar cap Green can and add a film bypass to the new bipolar cap in the global feedback loop. There is one for each channel. The amp will open up and imaging will greatly improve.
Mcgjohn, I have not run the original Mc tubes more that a week. I rolled many varieties of the 12AX7, many of them here already from my father's tube caddy which was last filled in the earlier 60's and never used after that. However, I was surprised to see that after 5 years of use, they no longer read solidly in my tube tester, the values just keep plummeting while under test.
No other tube does this, and when new, they didn't either, they were stable as a rock. As to modifying the amps, I'm not going to do that, only would do that if my service man suggests it and knows it to be without long term effects. I've got a nice stereo and adverse to taking risks. KA1J , Jun 20, You must log in or sign up to reply here.
Show Ignored Content. Share This Page Tweet. Your name or email address: Do you already have an account? No, create an account now. The lower gain tubes seem to cleanup some of the unwanted dirt in the preamp section of the amps from my reading. I thought I would loose some low end with the lower gain tube but, so far no difference. Maybe I can't tell since I am only using a few watts and would need some really spirited levels to hear a difference.
But, then I would have to leave the room due to the loudness, lol. It will depend on how your amp is biased and your preference of sound ultimately. My favorite running in two of my SE EL34 amps. I do like the sound of the 6CA7 in my amp. Just a nice thick lower end. I am liking the thick lower end of the 12AT7 also, lol. The Gold LionKT77's are not overly expensive. I still find myself in ear training to pickup the differences with these tube changes. I guess you can't get away from learning new things in this hobby.
Couple things to think about. The current difference is negligible, far greater current differences from switching the power tubes, for example. A 12AX7 in a 12AU7 slot with typical 12AU7 plate and cathode resistances will barely make any more gain than the 12AU7, if at all, since it's not operating in it's normal conditions. Depending on location in the circuit, the higher 2nd harmonic output of the 12AU7 could possibly be audible although probably subtle.
Of course, if you don't precisely level match at your listening position it will not be possible to make a sound pun intended judgment. There's also the issue of expectation bias another intended pun! I did not have expectation bias, I was more concerned about not causing any amp problems.
The 12UA7 in V2,V3 most likly will stay. I have not read about people substituting these tubes due to the very low gain. You know I start post in the tube section to pick the brains of some of our more experience tube affectionados. As far as expectation bias goes, I encounter that all the time when guys I know buy some really expensive tubes because they read that the "Tung-Sol gray plate type XXX with D getter and manufactured on January 3, " sounds better than any other tube of its type in existence.
No one has been willing to take me up on my offer to try their preference with a blind listening test in which they don't know what they are listening to. Maybe Dave can do a little post about this from a psychological point of view. It seems that when it comes to audio equipment, the prettier it is the better it sounds. And, certainly, the more expensive it is the better Klipsch forum has already taught me that more money spent is not always better.
I am not a cable, power cord or other super expensive things. Good setup, room Tx, good gear and quality source are my focus. This will give the greatest gains. No charge. I see them listed as a "low noise low microphonic 12AX7" But I dont know anything about them! I pulled them out of an old sony reel to reel.
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