1 Mar
2010
1 Mar
'10
8:49 p.m.
I've seen the same thing used for transformerless
phonographs, but
the cord was 3-wire, with the resistance wire being used to drop the
filament voltage. You'd see this on "crystal" cartridge phonographs
Yes, tapped line cordes were not uncommon over here either.
with a 3-tube setup that included a 50L6, 35Z5 and a
12-volt pre-amp
tube (varied). It was a real puzzle seeing a 2-prong plug ending in
3 leads...
M\ny of the cheap record palyers over here used a 1 or 2 vavle circuit.
The amplifier valve was something like a UCL82 (triode + output pentode),
the rectifier was either a UY85 or a selenium thing. But the normal way
to get the heater voltage was to tap the winding on the turntable motor,
and use that as an autotransformer.
We ahd some oddities in the radios too. One manufacturer half-wave
rectified the mains to get the HT (B+), os a hot chassis, but used an
autotransformer to run a series string of valves, not a dropping
resistor. Another used a double-wound transformer (and I think a
centre-tapped HT secondatry feeding a full=-wave rectifier), but the
heaters wrre still in series, with a suitable secodnary winding to run
that string. For the transformerless sets (often called 'AC/DC' sets over
here), some manufactuers used a barretter rather than a dropping
resisotr, and at least one set used a normal household light bulb for
that purpose (!).
Philips (IIRC) even made a transformerless valve output stage. 2 output
pentodes (EL84 and UL84, the latter because of the good heater-cathode
insulation IIRC) as a totem pole, with a high impedance speaker (800
ohms) from the centre tape to ground through a capactior. The speaker was
the main problem, it was wound with very thin wire (one reference says
0.3 thou diameter) and it was prone to go open-circuit.
-tony