USSR (various — Reflektor, Svetlana, Novosibirsk)Data: HighHigh quality — base, heater, all universal parameters present, and ≥50% of desirable parameters filled in. Safe to use for design decisions.
DHT (directly heated cathode) — the thoriated tungsten filament IS the cathode. Bias is applied between filament centre-tap and ground, or via a choke/DC source on one filament leg with cathode resistor referenced to the midpoint.
Filament can be wired for 2.1V @ 650mA (parallel, pins 1+7 to pin 8) or 4.2V @ 325mA (series, pins 1 to 7 with pin 8 unused).
Extensively used in modern audiophile single-ended triode-connected output stages. Typical triode-strapped operating point: Va=235V, Vg=-18V, Ia=40mA giving ~2.5W into 5kΩ.
In triode-strapped mode (g2 tied to anode): mu≈10, ra≈1.6kΩ, gm≈6 mA/V.
Maximum anode and screen voltages are both 250V — this tube is designed for low-voltage operation, not high B+.
Requires a proper DC filament supply for low-noise audio use; AC heating produces audible hum given the DHT topology.
Originally a Soviet copy of the German RL2,4P6 used in WWII-era military transmitters and radio equipment.