From fto–(at)–etcom.com Sun Mar 26 14:37:25 CST 1995
Article: 616 of alt.guitar.amps
Newsgroups: alt.guitar.amps
Path: geraldo.cc.utexas.edu!cs.utexas.edu!howland.reston.ans.net!ix.netcom.com!netcom.com!netcom19!ftom
From: fto–(at)–etcom.com (Tom May)
Subject: Interesting 12AX7 gain test results.
Message-ID:
Sender: fto–(at)–etcom19.netcom.com
Organization: The Planet Eden
Date: Sun, 26 Mar 1995 18:32:24 GMT
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Hi,

I decided yesterday would be a good day to test the gain in all my
12AX7s. I used a circuit with a 1M grid resistor, 68k grid stopper,
2.7k cathode resistor bypassed with 50uF, a 220k plate reistor (no
other load), and a 340V power supply. My input signal was 200Hz 100mV
p-p. I only tested one half of each tube, unfortunately.

Here is how they all stacked up, in descending order of gain:

Sovtek 12AX7WXT 78
Sovtek 12AX7WXT 76
German-made Realistic 12AX7A
(i.e. Radio Shack) 76
Sovtek 12AX7WXT 72
Sovtek 12AX7WXT 72
Hungarian 12AX7 68
GE 12AX7 64
Hungarian 12AX7 64
Hungarian 12AX7 64
GE 12AX7 58
RCA 12AX7A 48

The Sovteks are new.

The Hungarian tubes were in my amp when I bought it in the late 80s
and for all I know had been in it since it was manufactured in 1980.
It looks like the manufacturer is Tungsram, but the letters are all
fairly rubbed out.

The RCA had been in my amp 2 years. I don’t know if it was NOS or
just O when it was installed.

The GEs and Realistic are in an amp I’ve had since about 1982. The
Realistic was in a channel which hasn’t been used since at least 1982.

So I take back what I said about the Sovteks not having more gain than
the Hungarians (I said that somewhere). Also, either the American
tubes were not that great to begin with or they haven’t aged well.
–
Tom.