"Dave Plowman (News)" wrote in message
...

Pretty well all those old TVs had series heaters - so even if the valve
wasn't essential - unlikely - non of the others would work either.

My father bought our first TV from a neighbour in the trade. RGD. Cost the
equivalent of a very posh plasma these days. Which went wrong
frequently. Several new tubes fitted over its life. We got a new set when
ITV arrived, and I got to play with the old one. The tube was a re-gunned
one. But charged for as new.

Depending on when it was made your RGD may very well not have had series
heaters. The first set with no mains transformer and series heaters was the
Pye B18T of 1948, but other manufacturers, particularly up-market brands
like RGD, continued to fit mains transformers for several years after that;
though that didn't necessarily mean that the chassis was isolated from the
mains. Quite a few sets made in the early 1950s had a heater transformer,
and parallel fed heaters, but obtained the HT by direct rectification of the
mains. Sometimes the primary of the heater transformer acted as an
autotransformer for the HT thus avoiding the use of the tapped dropper
resistor otherwise necessary to cope with different mains voltages.

Some sets were really weird, with valves designed for series use, and thus
with non-standard heater voltages, fed from special windings on the
transformer. Sometimes individually, sometimes in short chains.

David.