7E5

The 7E5 is an indirectly heated loctal triode designed for high frequencies, with documented uses as signal source, local oscillator and RF amplifier. Sylvania describes oscillation up to 750 MHz in a double-ended transmission-line circuit. More than a generic transmitting-triode classification, its connection arrangement is part of the very-high-frequency design.

The envelope is T-9 glass and the base eight-contact loctal, with any mounting position permitted. Anode and grid have double symmetrical leads brought to the base from opposite ends of their internal structures. Sylvania relates this arrangement to transmission-line operation; Tung-Sol stresses relatively low interelectrode capacitances and lead inductance. Operating heater is 6.3 V and 0.15 A AC or DC; Sylvania distinguishes historical nominal 7 V and 0.160 A. With an external M8-308 shield at cathode, capacitances are 1.5 pF grid-to-anode, 3.6 pF input and 2.8 pF output.

At the class A1 characterization point of 180 V anode and −3 V grid, both sheets give 5.5 mA anode current, 3000 µmho or 3 mA/V transconductance and amplification factor 36. Tung-Sol gives 12 kΩ internal resistance; the consulted Sylvania sheet instead prints 120 kΩ, a discrepancy not turned into an average. Limits are 250 V anode, 16 mA anode current, 6 mA grid current, 4 W anode dissipation and 90 V heater-to-cathode. Permitted dissipation is not RF output to the load.

For 750 MHz UHF oscillation, Sylvania and Tung-Sol describe a half-wave four-line circuit, with tube-induced line shortening about 45% of a half wavelength. The examples use 200 or 250 V anode, 10 or 20 kΩ grid resistors and 11 or 13 mA anode currents, with developed biases of 2.5 or 3.5 V. These belong to the particular line configuration; the frequency figure does not promise identical performance in any assembly.

At 300 MHz a quarter-wave four-line oscillator or power amplifier is documented, with shortening about 30% of a quarter wavelength. With 150 V anode supply through 3 kΩ, 16 mA anode current, 6 mA grid current and about 1.7 kΩ grid resistor, stated output is 0.20 W. Another local-oscillator example uses 90 V supply through 3 kΩ, 7.8 mA anode current, −7 V grid and 3 kΩ grid resistor. Sylvania states useful power is obtainable at 400 MHz and below but recommends other types, including 7A4, below about 200 MHz. This defines its application range without claiming general superiority at every frequency.