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This set is a TRF type,
using three tuned stages and predates the superhet design. The
three tuned stages are enclosed in the large aluminium cans on
the right of the chassis.
The set uses three valves viz.
MM4V, 904V and Pen4V. Unusually it employs a large metal rectifier
to provide the HT. The power supply is conveniently located adjacent
to the loudspeaker which is energised by a large coil which doubles
as a smoothing choke.
All was present except the bronze
escutcheon (the bit through which one views the dial). My thanks
to John Gibson in California, who has one of these fine receivers
and very kindly sent me, not only a drawing of the escutcheon,
but a copy of the user's handbook and some interesting notes
and circuits. Surprise! I received a casting of the escutcheon
from John. He made it himself and it looks absolutely perfect,
even the right colour.
I now have no excuse to get
started on the refurbishment!
There is enough information
for me to make a replacement back panel, which was also missing.
I hadn't appreciated that the
power supply uses a voltage doubler. Why this is so is not that
easy to figure out. There are a few explanations...
1. First the high internal resistance
of the metal rectifier had been overlooked and the doubler was
an after-thought.
2. Secondly, the transformer
design originally catered for a valve rectifier but they forgot,
or later removed from the specification, the filament winding.
3. There was a reasonable saving
in the transformer cost with the smaller HT winding.
Any other explanations? |
