5B/254M

Beam Tetrode — Loctal

STC (Standard Telephones and Cables)

Known Equivalents & Substitutes

CV4285B/251M5B/255M5B/254GCV23475B/253M

Similar Tubes (Not Drop-In Compatible)

5B/257M

12.6V/0.47A heater variant — not pin-compatible due to different heater ratings

5B/258M

19V/0.3A heater variant — not pin-compatible due to different heater ratings

Electrical Specifications

Section 1 — Beam Tetrode

Absolute Maximum

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

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

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

Screen Dissipation (max)Screen Dissipation (max)3W

Notes

The anode connects via a top cap, not through the base pins. Top cap size is 1/4 inch (6 mm).
Cathode bias is not recommended per the manufacturer datasheet; fixed bias is required.
The 5B/255M is electrically identical. The 5B/257M is a 12V heater variant (12.6V, 0.47A). The 5B/258M and CV2347 are similar but with multiple differences.
Grid stoppers at the socket and RF chokes in the anode circuit may be required to suppress oscillation tendencies.
Pins 5 and 6 are both control grid connections (double grid pins), and pins 2, 4, and 7 are all cathode/beam plate connections.
Triode-strapped data sourced from Tom Schlangen, 'Overview of pentodes / BPTs strapped as triodes' (2009), not from the manufacturer datasheet.

Pin Layout — Loctal

1Heater

2Cathode / Beam Plates

3Screen Grid

4

References