DECCA CTV25

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When I bought this set the tube had a broken neck. A new
tube was fitted – an A63 -200X in place of the original A63 –
11X – and I am now trying to restore the set to working
order. The problem is sound but no raster, with the valves in
the line output stage running rather hot. All the valves in the
line timebase have been replaced, and I now suspect the line
output transformer. Any suggestions before I take this
expensive step? And is the replacement c.r.t. correct?
The replacement c.r.t. is suitable. The first step to take is
to see whether there’s a negative voltage of -30V or more
at the control grid (pin 1) of the line output valve. If not,
you will have to find out why the line oscillator is not
working – check around the PCF802, also the flywheel
sync circuit if necessary. If the negative voltage is present,
check the boost capacitor C413, the line output valve
coupling components C415 and L408, the focus rectifier
D401 and its reservoir capacitor C416, and the third
harmonic tuning capacitor C414. If all these are in order,
the line output transformer is suspect – it’s not over reliable
in this chassis. D401 and C416 can be checked simply by
disconnecting D401: if the valves then run cool, you’ve
found the fault.

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