Brans cross-lists in same group — Noval (9HF) vs Octal (8BD) base, different pin topology. Similar dissimilar dual triode but different Section 2 characteristics (gm=6.5 vs 7.2 mA/V, ra=925 vs 750 ohms)
Brans cross-lists in same group — Noval (9HF) vs Octal (8BD) base, different pin topology. Similar Section 1 (mu~64-68) but Section 2 differs (Pa_max 10W vs 10W, gm 7.5 vs 7.2 mA/V)
Heater-to-Cathode Voltage (max)Heater-to-Cathode Voltage (max)200V
Notes
Dissimilar dual triode: Unit No.1 (high-mu, pins 4/5/6) is a small-signal triode (mu=68, ra=40 kohm); Unit No.2 (low-mu, pins 1/2/3) is a power triode (mu=5.4, ra=750 ohm, Pa_max=10W).
The 6EA7 and 6GL7 are often considered interchangeable with the 6EM7 but have slightly different characteristics — 6EA7: mu 66/5, ra 30k/920 ohm; 6GL7: mu 66/5, ra 30k/780 ohm, heater 1.05A. Many tubes are double-stamped 6EA7/6EM7.
10EM7, 13EM7, and 15EA7 share the same 8BD pinout but have 10V, 13V, and 15V heaters respectively (series-string TV designs). Not interchangeable without heater supply modification.
The bulb becomes hot during operation — adequate ventilation and free circulation of air must be provided.
Popular in DIY audio as a single-tube amplifier: the high-mu section drives the low-mu power section, yielding ~1W SE output into a 4-5 kohm primary.
Pin Layout — Octal
1Grid (Unit No.2 - Low-Mu Triode)
2Anode (Unit No.2 - Low-Mu Triode)
3Cathode (Unit No.2 - Low-Mu Triode)
Socket-Compatible Tubes ⚠ Not electrically compatible