6EH5

The 6EH5 is a miniature power pentode designed for audio output stages in radio and television receivers and phonographs, explicitly stated by Tung-Sol and RCA; Sylvania likewise calls it an audio power amplifier. This seven-pin tube has documented single-tube and push-pull examples. The 12EH5, 25EH5 and 50EH5 belong to the same family, but their different heater characteristics remain essential when considering replacement.

The 6EH5 heater is 6.3 V, 1.2 A. Tung-Sol allows 6.3 ±0.6 V under voltage operation. Approximate unshielded capacitances are control-grid-to-anode 0.65 pF, input 17 pF and output 9 pF. Typical transconductance 14,600 µmhos equals 14.6 mA/V, a historical unit for the same quantity. Sylvania specifically identifies 12EH5, not the whole family, as having controlled warm-up and a different heater-cathode limit.

Typical class A1 uses anode-circuit supply 110 V, screen supply 115 V and cathode resistor 62 Ω. Idle anode current is 42 mA, idle screen 11.5 mA and maximum-signal screen 14.5 mA; approximate internal resistance 11 kΩ. With anode load 3 kΩ and peak grid signal 3 V, maximum example output is 1.4 W at 7% total harmonic distortion. Sylvania plots load against output and distortion; the preserved Tung-Sol curves are explicitly tentative and do not replace tabulated values.

Tung-Sol and RCA also give a two-tube AB1 push-pull example: anode supply 140 V, screen 120 V, cathode resistor 68 Ω and anode-to-anode load 6 kΩ. Output is 3.8 W at 5% total harmonic distortion, with peak grid-to-grid drive 9.4 V. Values are expressly for two tubes: idle anode current 47 mA and maximum-signal current 51 mA are not per tube. The load belongs to the output-transformer primary.

Rating systems remain separate. Sylvania uses design-center values: anode 135 V, screen 117 V, anode dissipation 5 W and screen dissipation 1.75 W. Tung-Sol and RCA use design-maximum 150 V, 130 V, 5.5 W and 2 W, with maximum envelope temperature 220 °C. They must not be combined into one set. Maximum grid-circuit resistance is 0.1 MΩ fixed bias or 0.5 MΩ cathode bias. Tung-Sol also separates heater-cathode peak limit 200 V from DC-component limit 100 V when heater is positive.

The miniature B7G base is identified as E7-1 with JEDEC 7CV wiring: 1 cathode and suppressor, 2 and 5 control grid, 3 and 4 heater, 6 screen, 7 anode. Tung-Sol gives maximum diameter 0.750 inch, height above pins 2.375 inches and overall height 2.625 inches: 19.05, 60.325 and 66.675 mm respectively; its wiring diagram is a bottom view. Any mounting position is permitted. Documentation: Sylvania two-page 6EH5/12EH5/25EH5/50EH5 sheet; Tung-Sol 6EH5, 1 January 1963 sheets and tentative curves of 1 September 1958; RCA Receiving Tube Manual RC-30, 6EH5 section pages 261–262; Precision 660 list used as instrument documentation.