EF762

The EF762 is a high-transconductance subminiature RF pentode intended by RFT for amplification at higher frequencies. The VEB Funkwerk Erfurt sheet of December 1956 is especially interesting because it gives tentative data and states that the tube is still in development. Its reference to the 5840 means similarity, not universal interchangeability. Heater 6.3 V, 150 mA.

Static characteristics refer to anode and screen 100 V, control grid −1.5 V: anode current 7.5 mA, screen 2.5 mA, transconductance 5 mA/V, internal resistance 250 kΩ. Screen-to-control-grid amplification factor is 36 and equivalent noise resistance 1.6 kΩ. The latter characterizes noise rather than specifying a resistor to add. The sheet states that lightface figures, unless limits, are approximate.

Limits give operating anode and screen 175 V, with 300 V cold ratings for both. Maximum dissipation is anode 0.8 W, screen 0.3 W; cathode current 12 mA, grid resistance 0.5 MΩ and heater-cathode voltage 100 V. Input capacitance is 4.2 pF with external shielding, 4.1 pF without; output respectively 2.5 and 2.0 pF. Control-grid/anode capacitance is 0.015 pF shielded, below 0.02 pF unshielded.

The eight-contact subminiature base has a functional diagram distinguishing anode, control grid, screen, two heater leads and three common cathode/suppressor leads. Wires allow direct connection of the small component. Maximum-dimension drawing: diameter 10 mm, glass body 38 mm and wires 40 mm separately; stated mass approximately 5 g. Wire length is not bulb height and does not establish an unstated overall dimension.

Documentation consulted: RFT, VEB Funkwerk Erfurt, EF762 tentative technical data, December 1956 edition, two pages of static data, limits, capacitances, connections and dimensions. Its development statement is part of the document and places the figures in context: they describe that sheet’s technical state. The edition date alone does not prove the start of series production.