21HD5

Beam Tetrode — Octal

Known Equivalents & Substitutes

6HD5

Similar Tubes (Not Drop-In Compatible)

Same tube family, same 21V/0.6A heater — verify exact interchangeability for specific application

Same tube family but 26.5V/0.45A heater — different heater voltage

Electrically identical but 6.3V/2.5A heater — not a drop-in in 21V series heater circuits

Electrical Specifications

Section 1 — Beam Tetrode

Absolute Maximum

Anode Voltage (max)DC Plate-Supply Voltage (max)990V

Screen Voltage (max)DC Screen Grid Voltage (max)190V

Anode Dissipation (max)Plate Dissipation (max)24W

Screen Dissipation (max)Screen Dissipation (max)3.2W

Cathode Current (max)Cathode Current (max, average)

Section 2 — Triode Strapped

Typical Operating

Anode Voltage (typical)Plate Voltage (triode connection)125V

Grid 1 Bias VoltageControl Grid Voltage (triode connection)-25V

Amplification Factor (μ)Amplification Factor (μ, triode connection)3.3—

Heater

Heater VoltageHeater Voltage21V

Heater CurrentHeater Current0.6A

Notes

21V heater version of the 6DQ5/6HD5 horizontal-deflection tube family. Heater current is 0.6A at 21V.
Brans Vademecum groups 21HD5 with 28GB5/PL500, 6DQ5, and 6HD5.
The plate (anode) connection is via a top cap for high-voltage insulation in TV horizontal deflection service.
Pins 1 and 5 are both Grid No.1; pins 3 and 6 are both Cathode/Suppressor Grid (G3); pins 4 and 8 are both Screen Grid (G2). Dual connections provide low-inductance paths.
Maximum peak positive-pulse plate voltage of 6500V applies only when pulse duration does not exceed 15% of one horizontal scanning cycle.

Pin Layout — Octal

1Control Grid (G1)

2Heater

3Cathode

Socket-Compatible Tubes ⚠ Not electrically compatible

References