Pictures of Japanese NEC 12AD7 Tubes

[kcline]

These came out of a early Sony R to R. Hard to find, as a retired tube dealer I have never seen more then a handful of these. Sockets in the r to r were marked 12AD7/ 12AX7

 

[larryderouin]

The only thing I see different in the spec's is the interelectrode capacitances which are very slightly higher in the 12ax7, and the heaters in the 12ad7 are higher amperage. Otherwise they are pretty much identical. You could sub a 12ax7 for the 12ad7, but beware of 12ad7 for a 12ax7 due to increased load from the heaters, especially if your heater circuit is close to maxxed out.

12ad7
Substitute Data

Preferred Substitutes ......................... 12AX7 12DF7
Substitutes ................................... 12BZ7
10782
Mechanical Data


EIA Outline ................................... 6-2
EIA Base ...................................... 9A
Electrical Data


Heater Voltage ................................ 6.3/12.6 V
Heater Current ................................ 0.45/0.225 A

Direct Interelectrode Capacitances (approx)
Triode
Input ......................................... 1.6 pf
Output ........................................ 0.5 pf
Grid to Plate ................................. 1.8 pf
Characteristics and Typical Operation

Class A Amplifier
Plate Voltage ................................. 250 V
Grid No. 1 Voltage ............................ -2 V
Amplification Factor .......................... 100
Plate Resistance (approx) ..................... 62.5K Ω
Transconductance .............................. 1600 µMho
Plate Current ................................. 1.25 mA

12ax7
Substitute Data

Preferred Substitutes ......................... 12DF7 12DM7
Substitutes ................................... 12AD7
Source ........................................ GE - 1973
10982
Application

Source ........................................ GE - 1973
Miniature type used as phase inverter or amplifier in ac/dc radio equipment and in many diversified applications such a multivibrators or oscillators in industrial control devices. Requires noval 9-contact socket.
Mechanical Data


Source ........................................ GE - 1973
Bulb .......................................... T-6 1/2
Base Type ..................................... Small Button 9-Pin
EIA Outline ................................... 6-2
EIA Base ...................................... 9A
Mounting Position ............................. Any
Electrical Data


Source ........................................ GE - 1973
Heater Voltage ................................ 6.3/12.6 V
Heater Current ................................ 0.3/0.15 A

Direct Interelectrode Capacitances (approx)
Each Triode
Source ........................................ GE - 1973
Input ......................................... 1.8 pf
Output ........................................ 1.9 pf
Grid to Plate ................................. 1.7 pf

Maximum Ratings (Design Center Values)
Each Triode
Source ........................................ GE - 1973
Plate Voltage ................................. 330 V
Plate Dissipation ............................. 1.2 W
Characteristics and Typical Operation

Class A Amplifier
Source ........................................ GE - 1973
Plate Voltage ................................. 250 V
Grid No. 1 Voltage ............................ -2 V
Amplification Factor .......................... 100
Plate Resistance (approx) ..................... 62.5K Ω
Transconductance .............................. 1600 µMho
Plate Current ................................. 1.2 mA

Source ........................................ GE - 1973
For other characteristics and typical operation, see 12AX7A