[ETO_Alpha] Alpha 91B - Problem

[py2xb at integral.com.br]

Any help here is appreciated

When using my alpha 91B (purchased in 1998), transmitting with normal
power output  (about KW out), suddenly the house circuit breacker opened.

When attempting to turn the amplifier back on, the 2ASB fuses blew in
every attempt.

Then I have oppened the amplifier, tooke the tubes out and unpluged  the
HV transformer connector. I found out that the circuit that makes K1 turn
on was faulty. I have replaced D1 (1N4007) on the AC Mains board as well
as R1 (560ohms) and it powered up again. I checked AC transfornmer
voltages and DC voltages (except HV which is unpluged). All ok. Amplifier
turns on (K1/K2) actve and 3 minute timer works.

Then I have made sure the DC HV path was not shorted by the cover safety
switch. Tubes still out. I have reconnected the transformer HV connector
to the PS board. Turned it on, and puff... D1 blew again.

I have checked the HV power supply : diodes, capacitors... . Everything is
ok.

My conclusion is that the transformer is bad. It is likely that there is 
lack of isolation between input and output. This has happen with 2 other
Alphas 91B purchased around the same year by PY fellows.

Is it something that others have experimented ???

thanks  Fred PY2XB