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In Reply to: RE: 12ax7, 12at7, 12au7 interchangability posted by Fishboat on January 08, 2008 at 10:44:27
What are you trying to accomplish? There is a huge gain factor between these tubes AU7 = 19; AT7= 60; AX7 = 100. Generally you can interchange AX7's for lower gain with an AT7. But a more typical swap for a 12AX7 would be a 5751. So, again, the question, "What are you trying to accomplish?"
AU7 has different electrical parameters although the pinout is the same.
Cheers,
Geary
Follow Ups:
Geary,
Much like many people I'm continuing the ongoing quest for that magic sound. I'm aware of the gain factor changes, maybe this is how I made a wrong turn somewhere in assuming the only difference between the three AU, AT, AX types was gain.
Sooo.. you're saying that a 12AT7 CAN be swapped into a 12AX7 circuit?
The plot thickens...apparently the answer is "it depends". I just checked the documentation(website) on my preamp and it says all three 12A?7's can be used...whew.
The CDP documentation says only 12AX7's..which is all it's seen.
Most likely your preamp uses the tubes as a buffer or as a cathode follower, in which case all types may be used. In voltage amplification circuits the various tubes may lead to problems, but generally in a cathode follower position I have successfully run the 12xx family with little or no issues.
Stu
The 12AX7, 12AT7, etc are different types of tubes. However, some tubes come in families (and people can even disagree about the "father") for example the 12AV7 family includes the 7062, the 5965 and one or two others. Members of a tube family are often close substitutes in almost any application, while substitution across types depends on the circuit and the role of the tube in that circuit.
There's a nice little interactive program you can download that allows you to look up a tube type, find the substitutes, plus it gives many of the specs for the tube and gives references more detailed information. It is called TDSL, or something like that.
The link is here
Greetings from the sunny Brønshøj riveria on the banks of the lovely Utterslev Mose
Fishboat,
Yes "depends" is the operative word. The phono stage in my preamp calls for 2 pairs of 12A*7 tubes. One stage can be 12AX7 or 12AT7, the other stage can be AU, AT or AX, but a switch must be changed for AU.
I am currently running 5751's for the first stage and 12AT7's for the second.
Seems that the older that I get the more important "Depends" become ;-)!!
Enjoy the music,
Geary
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