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12AX7 — Small Signal Triode, Noval | Tubeofile
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12AX7
Small Signal Triode — Noval
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Known Equivalents & Substitutes
ECC83
ECC803
ECC803S
7025
12AX7A
12AX7WA
12AX7S
M8137
CV4004
CV492
B339
B759
5721
6057
6681
7729
12DF7
12DT7
E2164
6L13
8339
E83CC
Similar Tubes (Not Drop-In Compatible)
12AT7
Same Noval dual triode pinout but medium-mu (mu=60) vs high-mu (mu=100); higher plate current, lower ra
12AU7
Same Noval dual triode pinout but low-mu (mu=17); much higher plate current, used as driver/buffer
12AY7
Same Noval dual triode pinout, medium-mu (mu=44); popular in early Fender guitar amp preamps
5751
Same Noval dual triode pinout, reduced mu (mu=70); military grade, common lower-gain substitute
6SL7
High-mu dual triode (mu=70) but Octal base; similar application as voltage amplifier
EF86
Noval pentode with similar high gain capability; different topology but used in similar preamp applications
Electrical Specifications
Absolute Maximum
Anode Voltage (max)
Max. Plate Voltage
300
V
Anode Dissipation (max)
Max. Plate Dissipation
1
W
Cathode Current (max)
Max. Cathode Current
8
mA
Heater-to-Cathode Voltage (max)
Max. Heater-Cathode Voltage
180
V
Max Grid Resistor
Notes
One of the most widely used small-signal tubes in audio, introduced in 1947.
The 7025 is a low-noise, low-hum version intended for high-gain audio preamplifier service.
The 5721 (12AX7WA) is the ruggedized military version with controlled heater warm-up.
The M8137 is the Mullard/CV military equivalent, highly sought after by audiophiles.
The 6057 and 6681 are GE special-quality versions with tighter parameter tolerances.
Can be operated with 6.3V or 12.6V heater supply using the pin 9 center tap.
The 5751 is often used as a lower-gain substitute (mu=70 vs mu=100) for reduced distortion.
Pin Layout — Noval
1
2
3
4
5
6
7
8
9
1
Anode 2 (Triode section 2)
2
Control Grid 2 (Triode section 2)
3
Socket-Compatible Tubes
⚠ Not electrically compatible
12AY7
12AZ7
12BH7
5751
A2900
ECC802S
References
https://www.drtube.com/datasheets/12ax7-rca1962.pdf
http://www.tubezone.net/pdf/12ax7ecc83.pdf
Max. Grid Resistor
2
MΩ
Typical Operating
Anode Voltage (typical)
Plate Voltage
250
V
Grid 1 Bias Voltage
Grid Voltage
-2
V
Anode Current
Plate Current
1.2
mA
Anode Resistance
Plate Resistance
62,500
Ω
Transconductance
Transconductance
1.6
mA/V
Amplification Factor (μ)
Amplification Factor
100
—
Capacitances
Grid-to-Plate Capacitance
Grid-Plate Capacitance
1.7
pF
Input Capacitance
Input Capacitance
1.6
pF
Output Capacitance
Output Capacitance
0.46
pF
Heater
Heater Voltage
Heater Voltage (series)
12.6
V
Heater Voltage
Heater Voltage (parallel)
6.3
V
Heater Current
Heater Current (series)
0.15
A
Heater Current
Heater Current (parallel)
0.3
A
Cathode 2 (Triode section 2)
4
Heater
5
Heater
6
Anode 1 (Triode section 1)
7
Control Grid 1 (Triode section 1)
8
Cathode 1 (Triode section 1)
9
Heater center tap