5B/256M

Name: 5B/256M
Brand: STC (Standard Telephones and Cables)

Beam Tetrode — Loctal

STC (Standard Telephones and Cables)Data: MediumMedium quality — at least 60% of universal parameters and pins are present, but some key data is missing. Verify specific values against datasheets before critical use.

↗ TDSL ↗ Radiomuseum

Known Equivalents & Substitutes

CV499

Similar Tubes (Not Drop-In Compatible)

5B/254M

6.3 V heater variant — same Loctal base and pinout but different heater voltage

5B/257M

12.6 V heater variant — same Loctal base and pinout but different heater voltage

5B/258M

19 V heater variant (CV2347) — verify if identical to 5B/256M or a different selection

Electrical Specifications

Absolute Maximum

Anode Voltage (max)Anode Voltage (max)600V

Screen Voltage (max)Screen Voltage (max)300V

Anode Dissipation (max)Anode Dissipation (max)25W

Typical Operating

Anode Voltage (typical)Anode Voltage (typical)300V

Notes

The anode connects via a top cap, not through the base pins.
19 V / 0.3 A series heater — designed for series-string operation.
Total anode and screen dissipation under 25 W.
Class AB2 audio (pair): 80 W RMS. Class C at 60 MHz (pair): 40 W at 600 V anode.
Brans lists as equivalent to 5B/250A, 5B/251M, 5B/253M, 5B/254G, 5B/254M, 5B/255M, 5B/257M, 5B/258M families.
Pins 5 and 6 are both control grid connections (double grid pins), and pins 2, 4, and 7 are all cathode/beam plate connections.

Pin Layout — Loctal

1Heater

2Cathode / Beam Plates

3Screen Grid

4

Socket-Compatible Tubes ⚠ Not electrically compatible

5B/254M 5B/257M 5B/258M

References