[unclemanly]

Originally Posted by 60136 Alcazar

These are all B5 based valves, which further supports the pre-1933 date since the B7 base was introduced from 1933 for new developments. The unmarked valve is most probably a triode (it looks like a Marconi MH4). Given the presence of the AC/SG and AC/PEN (both Mazda B5 based with side contact), this may originally have been an AC/HL, but set makers in the 30s did not always use a single valve manufacturer in their line-ups.Total HT current would therefore be around 42 mA. All the heaters are rated at 4 volts, 1 amp. The original rectifier could be expected to have a similar heater rating, and be capable of delivering 60 mA, so, on the assumption that indirect heating was a requirement (to limit the charging rate for the smoothing capacitors), a Mazda UU2 (equivalent to Brimar R1 and Ever-Ready S11A) should fit the bill. The only proviso is the measured AC voltage being applied to the anodes, which for these valves should be 250V AC or less. If more than this and less than 350V AC, then a more modern rectifier would be needed.

High current rectifiers were introduced in 1933, so it may just be that an MU12, IW3 (later IW4/350), or A11B was indeed fitted to the PSU as it may have had other applications besides this radio. Although frequently regarded as equivalent to the MU12, and sometimes marked as MU12/14, the MU14 will deliver higher voltage at higher current than the MU12. Pre-war higher efficiency specimens were extracted from the production batch and marked MU14, whilst the less efficient ones were marked MU12. Much later production saw them marked MU12/14.

Thanks for that info. The power supply and the radio chassis look to be much of a piece with each other so I doubt the power supply was some general purpose unit. In that case I'd better keep an eye out for a UU2 rectifier.