26 Feb
2010
26 Feb
'10
7:26 p.m.
On 25 Feb 2010 at 6:22, Tony Duell wrote:
Ah, TV sets over here rarely had power transformers at all, and if they
did they were likely to be autotransformers. Every valved monochrome TV
Iv'e worked on (and most that I've seen the service sheets for) had a
300mA series string of valve heaters and got the B+ line by half-wave
rectifying the mains. The EHT came from the horizontal flyback, of
course, as did the 'boost supply', taken from the primary of the
horizontal output transformer. This was around twice the HT+ voltage (say
400V or so) and was used as the supply to the horizontal output stage and
sometimes other stages too.
Colour sets often had a mains transformer, but it wqs an autotransformer
for the HT+ and series-string heaters, with a separate 5.3V widnign for
the CRT heater only. Not a particulalrly useful part for homebrewing.
And of course out horizontal output valves had strange heater reatings
(300mA current, at 30-40V depending o nthe type IIRC). Again not too useful.
You were more likely to find a amins transformer in a large valve radio
(you's get 6.3V at 2 or 3A, 350-0-350V and often a separate 4V or 5V
winding for the rectifier heater). Of course later radios used
series-string heaters (often 100mA) and no transformer.
-tony
Presumavly you wanted the line output valve
('sweep tube'?) from the
latter to use as the transmitter PA.
Oh, much more than that--the radio was the source of variable
capacitors, but the TV was the treasure trove. A huge power
transformer, rectifier (usually something like a 5U4), filter caps,
horizontal output tube(s) (Some early sets used push-pull 6BG6s;
later ones just ran the horizontal output tube to within an inch of
its life. Plus =E7a change...). The exciter could be a 6SJ7, from the
video output stage.