1 Mar
2010
1 Mar
'10
9:40 p.m.
On Mon, 1 Mar 2010, Tony Duell wrote:
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 (!).
In the US, there was the All-American Five design that was used by nearly
all manufacturers for the lower end models. The heaters were wired in
series and the voltage drop added up to 121. That was close enough for
120VAC and thus the transformer could be omitted.
--
David Griffith
dgriffi at cs.csubak.edu
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