Hi Pete, I suggest you do more testing before writing off the transformer.
One failure scenario that would cause the described problem is a surge
limiting circuit that is not shorting out the limiting resistor in the primary
circuit.
If you measure the 240/120vac line voltage right at the plate transformer
primary, it should be quite steady during turn on.
If that checks ok, you can carefully do the same test on the transformer
secondary. It should also be quite steady at turn on.
Happy hunting!
73,
Gerald K5GW
In a message dated 6/6/2011 2:07:13 P.M. Central Daylight Time,
pete@soper.us writes:
Folks,
A bug deposited a big glop of mud (+ larvae) into the gap between one
of the PS caps of my Titan and also glued the top of the cap to the side
of the power supply metal cover. The cover and the rest of the case was
very well grounded and the PS fuses never blew, the amp just stopped
working. I have no idea how long a mud/dirt short was in place, but the
larvae obviously didn't make it out alive.
The cap in question tested obviously bad and I made an exact
replacement. All eight caps now behave the same now, except the voltage
across each varies by 1-5%.
I spent a few days reforming the caps while fretting that the
transformer/rectifier by itself is only putting out about 1300 volts in
the "high" setting.
With the caps in place there is only 1650 volts present (i.e. about
550 volts short of spec). If a 14 watt signal is put into the amp
briefly the plate voltage dives to about 1kv and comes back to 1650 over
the course of 3-4 seconds. All of the rectifiers are open one way and
dropping 1/2 volt the other way (with a meter having a diode test
position).
Am I correct to think the transformer is toast?
Regards,
Pete AD4L
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