The envelope is helpful with just the No. 3A as a Type designation. A visual search indicates the SP13C as the most likely actual valve type and the dimensions match exactly. Civilian wireless valves during WWII were styled BVA but 3A has no meaning in this context.The SP13C from Mullard is a screened amplifier HF pentode. The similar SP13 has a CT8 base. The control grid is taken to the top cap for maximum isolation between input and output circuits. This valve was used in RF and IF stages of domestic radio receivers with a common heater chain and used for Universal AC/DC sets.
The reverse carries the Mullard name but no logo.The classic envelope is 40 mm in diameter and, excluding the B7 base pins, is 105 mm tall.References: Data-sheet, 1040 & 1043. |
Pin Connections
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | tc |  m | a | g3 | h | h | k | g2 | g1 |
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Absolute Maximum Operating Conditions¶
| Vh | Ah | Va | Vs | Vg | mAa | mAs | ra | gm | 
| 13.0 | 0.2 | 200 | 200 | -2.2 | 2.5 | 0.9 | 2.5M | 2.8 |
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Updated April 08, 2026.
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