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5B/257M — Beam Tetrode, Loctal | Tubeofile
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5B/257M
Beam Tetrode — Loctal
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STC (Standard Telephones and Cables)
Data: Medium
Medium 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
CV2220
Similar Tubes (Not Drop-In Compatible)
5B/254M
6.3 V heater variant — same Loctal base and pinout but different heater voltage
5B/255M
Similar 12 V heater variant with slightly different selection
5B/256M
19 V heater variant — same base but different heater voltage
5B/258M
19 V heater variant (CV2347) — same base but different heater voltage
Electrical Specifications
Absolute Maximum
Anode Voltage (max)
Anode Voltage (max)
600
V
Screen Voltage (max)
Screen Voltage (max)
300
V
Anode Dissipation (max)
Anode Dissipation (max)
25
W
Typical Operating
Anode Voltage (typical)
Anode Voltage (typical)
300
V
Notes
The anode connects via a top cap, not through the base pins.
12.6 V / 0.47 A heater — designed for 12 V supply equipment.
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.
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
1
2
3
4
5
6
7
8
1
Heater
2
Cathode / Beam Plates
3
Screen Grid
4
Socket-Compatible Tubes
⚠ Not electrically compatible
5B/254M
5B/256M
5B/258M
References
https://tdsl.duncanamps.com/show.php?des=5B/257M
https://www.radiomuseum.org/tubes/?tube=5B/257M
Screen Voltage (typical)
Screen Voltage (typical)
250
V
Grid 1 Bias Voltage
Grid 1 Bias Voltage
-45
V
Anode Current
Anode Current (typical)
72
mA
Transconductance
Transconductance
6
mA/V
Output
Output Power
Output Power (2 tubes, Class AB2 audio)
80
W
Noise / RF
Max Operating Frequency
Max Operating Frequency
125
MHz
Heater
Heater Voltage
Heater Voltage
12.6
V
Heater Current
Heater Current
0.47
A
Cathode / Beam Plates
5
Control Grid
6
Control Grid
7
Cathode / Beam Plates
8
Heater
TC
Top Cap —
Anode (top cap)