5B/258M

Name: 5B/258M
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

CV2347

Similar Tubes (Not Drop-In Compatible)

5B/254M

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

5B/255M

Related variant in the same family

5B/256M

19 V heater variant (CV499) — verify if identical or a different selection

5B/257M

12.6 V heater variant — same base but different heater voltage

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.
The 5B/256M (CV499) and 5B/258M (CV2347) are both 19 V heater variants — they may differ in selection criteria or specification tolerances.
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/256M 5B/257M

References