ECC802S

The ECC802S is a twin triode with separate cathodes for low-frequency applications, with nominal amplification factor 17. Tesla's December 20, 1960 sheet documents its use as a voltage amplifier and phase inverter, as well as in multivibrators and blocking oscillators. It has an all-glass miniature envelope and nine-pin Noval base. The sections are independent: anodes on pins 1 and 6, grids on 2 and 7, cathodes on 3 and 8; heater ends on 4 and 5 with centre tap on 9. Indirect heating accepts DC or AC, at 6.3 V and 300 mA with the halves in parallel or 12.6 V and 150 mA in series.

AEG and Tesla specify per section, at 250 V anode voltage with an 800 Ω cathode resistor, nominal current 10.6 mA, transconductance 2.2 mA/V and internal resistance 7.7 kΩ. Telefunken and JJ give 10.5 mA at the same point, retaining 2.2 mA/V, 7.7 kΩ and factor 17. The curves show current versus anode and grid voltages, and parameter changes with operating point. Telefunken pairs the designation with 6189 and states compliance with MIL-E-1/246 C requirements for type 12AU7WA; JJ lists 6189 among substitutes. Tesla instead cites 6067 as a foreign type replaceable by its ECC802S: these are individual-source statements to retain in context.

The historical documents emphasise long life, tight tolerances, reliability and mechanical resistance. Telefunken guarantees 10,000 hours averaged over 100 valves provided heater voltage stays within ±5% of nominal; it also describes a special cathode resistant to interface-layer formation while heated without anode current. A particular detail is a test of at least 2,000 cycles, one minute on and one minute off, at 7.5 V heater voltage and the manufacturer's other stated conditions: the test value is not nominal service voltage. Tesla also documents 32 hours of vibration at 50 Hz and 2.5 g, single shocks of 500 g and climatic tests. JJ describes its version as non-microphonic, while Tesla provides a specific microphonics test with a 0.3 mV limit under stated conditions.

Specifications differ across production versions. AEG and Tesla give per-section maxima of 300 V operating anode voltage, 550 V cold, 2.75 W dissipation and 15 mA continuous cathode current. Telefunken gives 330 V, 600 V without current, 3 W and 22 mA; JJ gives 330 V, 3 W and 22 mA. AEG limits grid resistance to 1 MΩ with automatic bias and 0.25 MΩ with fixed bias; Telefunken gives 1 MΩ and 0.5 MΩ respectively. The heater-to-cathode limit is 100 V in the sheets considered. These differences explain why the designation must be read with the applicable datasheet: the ECC802S combines documented audio and circuit functions with quality requirements to interpret for the actual production.