The TH4 is a triode hexode mixer dating to 1936. The later variants are: TH4A (1937) and TH4B (1938).In the 1930s the UK still had a mix of AC and DC mains supplies and so called 'universal' sets were made with series heater chains and the HT taken from the mains via a rectifier - redundant on the DC mains of course. Mullard made the TH21C which was the TH4 with a 200 mA heater for these sets. If the mains plug was wired incorrectly the chassis would be live and thus potentially lethal.
The reverse is plain gold coloured zinc paint.The classic envelope is 45 mm in diameter, and excluding the B7 base pins is 115 mm tall.References: Data-sheet & 1043. Type TH4 was first introduced in 1936. See also 1936 adverts. |
Pin Connections
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | tc |  a(t) | g1(t),g3 | g2,g4 | h | h | m,k | a | g1 |
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Absolute Maximum Operating Conditions¶
| Vh | Ah | Va | Vs | Vg | mAa | mAs | ra | gm | 
| 4.0 | 1.5 | 250 | 70 | -2 | 4.0 | 6.0 | 1.5M | 1.0 |
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Absolute Maximum Operating Conditions¶
| Va | mAa | gm |
| 150 | 6.0 | 1.2 |
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Thanks to Andy Cowley for supplying the above PDF datasheet. |
Updated August 05, 2015.
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