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.

Index:

12AX7 Comparisons	12AX7 gain test	12AX7 vs 12AT7	12AX7 vs 5751
12AX7 vs 7025	5881 in Deluxe	5881=6L6GB	5AR4 data
5AR4 Typing	5V4 for 5AR4	62 Twin Speakers	6550s in Twin
6EY6 Characteristics	6EY6 close to 6V6	6EY6 rating vs 6V6	6EY6
6L6 GC meaning	6L6 Taste Tests	6L6 Types	6L6GC ID
6L6WGB vs 7581	6MB8 tube specs	6V6 6L6 swaps	6V6 duty cycle
6V6 NOS vs Sovtek	6V6 Ratings	6V6 Russian RCA Copies	6V6 to EL84 Cathode Resistor
6V6 Types	6V6=7408	6V6EH Taste Test	6V6EH vs RCA Blackplates
6V6GT Types	6V6GT vs GTA	6V6s in 6L6 amps	7408 info
7581A tubes	7868 equivalents	Amperex history	Best 6V6
Blue Glow Sylvania	Breaking in Tubes	Breathe on tubes	Brimar Special Quality
CEI 6V6GTs	Chinese 12AT7s	Chinese 6V6GTBC	Design Max Rating
EL34 coding explained	Euro Tube Code	Fingerprints	Fuzzy Cathodes
GE and Sylvania	Groove Tubes 6V6HD	Groove Tubes testing	Groove Tubes
GZ34 types	GZ34 Varieties	GZ37 vs 5U4	How Are Tubes Made
Hytron tubes	ID Tube Makers	Identify Tube Makers	Is Tube Matching Needed
LV Visseaux 6V6 Warning	M	Making Tubes	Mazda History
Metal 6V6s	micKtubes	More M	New US 6L6GCs
No More Chinese 12AX7s	Overvoltage Effects	Phillips 6L6GB JAN	Photon Noise
Real Mullard GZ34s	Relabeling	RTV Tube Damping	Ruby 6V6GTBC
Sovtek 12AT7EH 5751 Test	Sovtek 5881 Confusion	Sovtek 5881 data	Sovtek 5881 for 7027
Sovtek 5881 specs	Sovtek 5881	Sovtek 5881WXT	Sovtek 6CA7 problems
Sovtek 6L6WXT+	Sovtek Midget	Sovtek Online	Sovtek page
Sovtek Tube specs	SPICE tube models	Standby Switches	SV 6L6GC
Svetlana 6550s	Svetlana 6L6GC	Svetlana 7591A	Svetlana EL34 review
Telefunken placement	Telefunken Tubes	Tesla 12AX7	Tesla 6L6GC
Tomorrows tubes	Tube Amp Books	Tube Amp FAQ Feb 96	Tube Chickens
Tube Curve Tracers	Tube Data Page	Tube Data Web site	Tube Failures
Tube gas avalanche	Tube heating effects	Tube Manufacturers	Tube Mfgr Codes
Tube mismatch harmonics	Tube Naming Explained	Tube rejuvenation	Tube Relabeling
Tube Stability	Tube types	Tubes for sale	Tubes vs SS
Visseaux 6V6 Warning	Visseaux 6V6	Vudu Tube Replacement	What Does 6L6GC Mean
What is 5881	What is 7027	Which Rectifier	Why 5V rectifier vs 6
Why 6	Why Tubes Coated Inside	Worn Out GZ34s	YA tube page