When the power switch is ON there is the HV also applied. Thus I wouldn't
expect shorted tubes or any HV component. Likely the bias diode shorted
thus when switched to Operate the tubes fully conduct and take out the fuse.
Watch for Plate current to peg.
With amp ON and the Operate switch in Standby, you should be able to see the
HV on the meter. The Operate switch basically changes the control mode,
thus the internal T/R switching is activated.
73
Bob, K4TAX
----- Original Message -----
From: "Bry Carling" <bcarling@cfl.rr.com>
To: <tentec@contesting.com>
Sent: Thursday, January 30, 2014 2:30 PM
Subject: [TenTec] 422 Centurion blowing fuses...
I have a Tentec 422 Centurion that is blowing the main 20 Amp fuses...
Looking for insights to this amp failure. It started spontaneously.
I can turn on the main power OK and the filaments light up on the
3-500Zs. The 12 volt power supply is OK because the pilot lights come on.
However when I flip the standby - operate switch to the Operate positionm
the fuse or fuses will blow. I replaced them with good 250V 20A cuses.
I checked the plate transformer windings and everything seems normal for
all three windings. Nothing is shorted. The safety ground for the
cover-open condition is not
across the HV plate supply. I checked that nothing else is shorting out
the plate supply
either.
Does anyone have any idea what might be going on here?
Many thanks - Brian Carling, AF4K
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