 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
73.239.123.14
In Reply to: RE: Different function of 12au7s and 2 12ax7s in amplifier. posted by TGT on February 02, 2016 at 10:28:43
Without looking at a schematic, it's anybody's guess!
A 12AX7 and 12AU7 are different hammers for different nails, but having two of them in each monoblock leaves a lot of room for guessing their exact purposes.
Follow Ups:
Since the 12AX7 has far more gain than the 12AU7, then it is used for amplification and the 12AU7 serves some other function?
The 12AX7 has a lot of voltage gain, but if anything but the bare minimum of drive current is needed, it's not a great choice.
Typically you'd see a 12AX7 as the first stage, then something like a 12AU7 serving as a phase inverter.
In your case, that leaves you with one extra 12AU7 and one and a half 12AX7's that are either wrapped up in the above topology, or perhaps are doing regulator duties.
If that is the case, would the 12ax7 contribute more to the sonic signature than the 12AU7?
Hi
It is impossible to say without seeing the schematic. As a gross rule of thumb, in many integrated amps changing the preamp tubes will have a little more effect than changing the drivers and the output tubes will have the least effect. But that is a terribly gross generalization and it will depend on the circuit. Also the initial quality of the tubes before you change them. There are many circuits where a 12bh7 can be used in place of a 12au7 as well, but without seeing a schematic it is impossible to know.
TGT,
usually the sound character can be set by the first tube in the circuit, but not always. also depends on how much global feedback is used. If a lot is used, you may not hear much difference between tube brands of the same type.
Just going from memory, the
12AX7 was 99 db of gain
12AU7 was 20db of gain
12AT7 was 60 db of gain
12AY7 was 40? db of gain.
since NOS or UOS (Used old stock) US made input tubes can still be obtained pretty cheaply, you might want to try finding some US made RCA, Sylvania, GE made tubes of the same type and experiment there first.
happy listening,
J
If I might offer a couple corrections...Tubes do NOT have gain, tubes have mu, and as a result the CIRCUIT they are in has gain. Also, mu (or gain as you described it) is not expressed in db.
So in a few specialized circuits (using a stout CCS for instance) a 12AX7 might approach a gain of 100, but in a cathode follower it won't even have a gain of one.
The mu of the tubes you mentioned does vary some with the current, voltage, etc. the tube is seeing, but the "spec" is:
12AX7 - mu of 100 @ 250 plate volts
12AU7 - mu of 17 @ 250 plate volts (20 at 100 volts)
12AT7 - mu of 60 @ 250 plate volts
12AY7 - mu of 44 @ 250 plate volts (I've also see slightly different figures, but all in the 41-44 range)BTW - 40 db would be a voltage gain of 100, and 99 db would be approaching a gain of 90,000!
We've come to use mu and gain interchangeably when describing tubes, but there IS a major and important difference!!
Edits: 02/05/16
Post a Followup:
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]