851 — Power Triode, Jumbo3 | Tubeofile

851

Power Triode — DHT — Jumbo3

RCA

Known Equivalents & Substitutes

CV2671VT-41GL-851PR-51-ACG-217238151

Similar Tubes (Not Drop-In Compatible)

Smaller transmitting triode (100W Pa_max) with mu=5.3 and UX4 base; much lower power and different mu

Same Jumbo3 base transmitting triode with 300W Pa_max and mu=19; electrically similar but half the power capability of the 851

Electrical Specifications

Absolute Maximum

Anode Voltage (max)Plate Voltage (max, Class B/C)3,000V

Anode Dissipation (max)Plate Dissipation (max, Class B/C)750W

Cathode Current (max)Plate Current (max)1,000mA

Typical Operating

Anode Voltage (typical)Plate Voltage (typical, Class A)2,500V

Notes

DHT tube: the thoriated tungsten filament serves as the cathode; there is no heater-cathode isolation.
The plate (anode) connection is via top cap No. 1902; the base (No. 3117) carries only filament and grid connections.
Amplification factor (mu) = 20.5. Direct interelectrode capacitances: Cgp=47 pF, Cgk=25.5 pF, Cak=4.5 pF.
Class A AF amplifier/modulator: Va_max=2500V, Pa_max=600W. At Va=1500V: Vg=-40V, Ia=175mA, ra=1800 Ohm, rl=3700 Ohm, Po=46W. At Va=2000V: Vg=-65V, Ia=270mA, ra=3100 Ohm, rl=3700 Ohm (sic), Po=100W. At Va=2500V: Vg=-92V, Ia=240mA, ra=1600 Ohm, rl=5000 Ohm, Po=160W.
Class B AF amplifier/modulator (2 tubes): Va_max=3000V, Pa_max=750W. At Va=2000V: max-signal Ia per tube=1.7A, rl per tube=650 Ohm, Po=20W driving, 2.2W output. At Va=2500V: max-signal Ia=1.4A, rl=1000 Ohm, Po=12 approx.W driving, 2.3W output. At Va=3000V: max-signal Ia=1.2A, rl=1400 Ohm.
Class B RF power amplifier (telephony): Va_max=2500V, Pa_max=750W per tube. At Va=2000V: Vg=-85V, peak RF grid voltage=140V, Ia=0.475A, Po=275W approx.
Class C plate-modulated RF amplifier (telephony): Va_max=2000V, Pa_max=500W. Capable of 900W output at Va=1500V and 1250W at Va=2000V.
Class C RF oscillator (telegraphy, key-down): Va_max=2500V, Pa_max=750W. Capable of 900W output at Va=1500V and up to 1700W at Va=2500V.
Maximum plate current is 1000 mA (1A). Requires forced-air cooling at full ratings.

Pin Layout — Jumbo3

1Filament

2Grid

3Filament

TCTop Cap —Plate (Top Cap)

Socket-Compatible Tubes ⚠ Not electrically compatible

References