35EH5

The 35EH5 is a seven-pin miniature audio output valve, described as a power pentode in the RCA and Tung-Sol sheets examined. Its 35 V heater draws 150 mA; RCA permits AC or DC and specifies ±10% voltage tolerance. Tung-Sol's August 1, 1960 sheet calls it similar to the 50EH5, but this does not make heater supplies interchangeable or justify automatically assigning other family types' data.

Typical class A1 audio operation uses 110 V anode supply, 115 V screen supply, 62 Ω cathode resistor and 3 kΩ anode load. With 3 V peak control-grid signal, stated output is 1.2 W at 8% total harmonic distortion. Anode current is 32 mA at both zero and maximum signal; screen current rises from 7.2 to 12 mA. Approximate anode resistance is 14 kΩ and transconductance 12 mA/V. Maximum 5 W anode dissipation is an electrode limit, not this circuit's audio output.

RCA supplements the table with a load-dependent performance curve. Conditions include the same 110 and 115 V supplies, 62 Ω cathode resistor, 100 µF bypass capacitor and 2.1 V RMS signal. The graph shows power and distortion together: increasing load alone does not increase power indefinitely, and the distortion minimum belongs to a specific part of the curve. Another chart gives anode characteristics and screen currents at 115 V screen for different grid biases.

Limits use the design-maximum system: anode 150 V, screen 130 V, anode dissipation 5 W, grid 2 input 1.75 W. The control grid must not have positive bias. Maximum grid-circuit resistance is 0.1 MΩ with fixed bias and 0.5 MΩ with cathode bias. RCA also limits the hottest bulb surface point to 225 °C. These limits are separate from typical conditions and require their operating context.

Heater-cathode voltage depends on polarity. With heater negative to cathode, maximum total DC and peak is 200 V; with heater positive, total may be 200 V but DC must not exceed 100 V. Capacitances without external shield are approximately 0.65 pF control-grid-anode, 17 pF input and 9 pF output in the specified connections. These details extend the description beyond audio wattage alone.

The E7-1 miniature base is seven-pin, basing 7CV viewed from below: 1 cathode with grid 3, 2 control grid, 3 and 4 heater, 5 second control-grid connection, 6 screen, 7 anode. Any mounting position is permitted. Documents agree on maximum overall length 2 5/8 inches and maximum seated height 2 3/8 inches, or 66.675 and 60.325 mm. Tung-Sol gives maximum diameter 3/4 inch; RCA gives 0.650–0.750 inch, or 16.51–19.05 mm.

Documentation consulted: Tung-Sol, 35EH5 Pentode, Tentative Data, August 1, 1960, one page; RCA, 35EH5 Power Pentode, Data 1 and Data 2, August 1960, four pages with data and curves, compared in both archived copies.