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frank frank is offline
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Default Amperex M24-302W equivalent?

wrote:
Can you get a wire in between the flyback coil and core ? If so you just
make your own winding that is totally floating. Start with one turn and work
your way up until the filament is bright enough.


never mind, it wasn't a short circuit in the CRT. It was me supposing
the cathode should cutoff at 0V, instead it was supposed to cutoff at
something like 20-30V.
One amplifier stage was bad, a 2N2369 tested good on a diode probe (both
junctions!!) and it was not amplifying at all, just passing the signal
through the base-collector junction, so not inverting it.
The end signal at the catode was "upside down".
Replacing the 2N2369 cured the monitor (well, geometry isn't the best, but
I won't mess with it).


It is better if you have measuring equipment. A true RMS meter can read the
waveform at 6.3 volts RMS but not everyone has that. A scope should show
about 20 volts peak to peak, that corresponds to about 6.3 volts RMS with
that waveform which is usually a half sine resonated at 5 times the
horizontal sweep frequency. Iff the monitor has fast retrace it might have
to be a bit higher. In any case, use as little as possible to get a decent
display. The less the better as it will result in the longest cathode life.
The cathode has already been abused putting out more current than was ever
intended.


I have scopes and other test instruments (like a few true RMS meters) and
I'm glad I just needed the scope to find the bad stage, once I realized I
needed a positive voltage to cutoff the cathode.
The first common-emitter stage didn't invert the signal, so it was easy
to spot.

This monitor is 41 years old by the way

Thanks
Frank