To the best of my knowledge, it was only Mullard who produced 'magic eyes' on the side-contact base. The possibilities are TV4, EM1, EM3 and EM4. Identification can be determined by inspection of the valve socket wiring and a heater voltage measurement. The TV4 is the only one with a 4-v. heater; the others are 6.3-v. The EM1 is effectively a 6.3-v. version of the TV4. The EM3 is a more sensitive version of the EM1. The EM4 is a dual sensitivity version of the EM3.
Pin-outs, TV4, EM1 and EM3:
1 = heater
2 = no connection
3 = anode
4 = target
5 = grid
6 = no connection
7 = cathode
8 = heater
Pin-outs, EM4:
1 = heater
2 = no connection
3 = anode 1
4 = target
5 = grid
6 = anode 2
7 = cathode
8 = heater
As for "where to begin", I'd suggest as per any piece of unknown, vintage electronics. A thorough 'no power applied' visual inspection first, correcting any obvious deficiencies, followed by an initial power-up via a Variac or lamp-limiter. The rest is the 'standard overhaul & fix procedure' that we are all familiar with.
Al.
Pin-outs, TV4, EM1 and EM3:
1 = heater
2 = no connection
3 = anode
4 = target
5 = grid
6 = no connection
7 = cathode
8 = heater
Pin-outs, EM4:
1 = heater
2 = no connection
3 = anode 1
4 = target
5 = grid
6 = anode 2
7 = cathode
8 = heater
As for "where to begin", I'd suggest as per any piece of unknown, vintage electronics. A thorough 'no power applied' visual inspection first, correcting any obvious deficiencies, followed by an initial power-up via a Variac or lamp-limiter. The rest is the 'standard overhaul & fix procedure' that we are all familiar with.
Al.
