5B/254A

Beam Tetrode — UX5

STC (Standard Telephones and Cables)

Known Equivalents & Substitutes

CV4288075B/250A

Similar Tubes (Not Drop-In Compatible)

5B/254G

Electrically identical but uses flexible leads for direct wiring — different base/connection

Electrically identical but uses Loctal (B8G) base — not pin-compatible with UX5

Electrically identical but uses Loctal (B8G) base — not pin-compatible with UX5

Electrical Specifications

Section 1 — Beam Tetrode

Absolute Maximum

Anode Voltage (max)Anode Voltage (max, Class AB2/RF)600V

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

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

Screen Dissipation (max)Screen Dissipation (max)4.5W

Notes

The 5B/254A is the UX5-based variant of the 5B/254M (Loctal B8B base). Electrically identical; only the base differs. The 5B/254G is the same tube with flexible leads for direct wiring.
The anode connects via a top cap, not through the base pins. This is essential for high-voltage insulation.
Cathode bias is not recommended. Fixed bias is required; the DC grid circuit resistance should not exceed 30,000 ohms at maximum ratings.
Datasheet operating values for AF push-pull configurations are given for 2 valves; per-valve output is half the stated value.
For high-altitude or anode-modulated operation, STC recommends the double-ended versions (5B/254G, 5B/254M, 5B/258M) due to insulation considerations at the valve base.
The 5B/254A is not explicitly listed on the STC datasheet (Ref. 5B/254G to 5B/258M, June 1961/January 1963). Data is derived from the 5B/254M specifications which are electrically identical.

Pin Layout — UX5

1Heater

2Screen Grid (g2)

3Control Grid (g1)

4Cathode

5

Socket-Compatible Tubes ⚠ Not electrically compatible

References