Steve Katz wrote:
> > When the unit is powered up the primary fuses blow once the HV switch is
> > enabled. The filament power appears to be ok. I have removed the tubes and
> >
> > ruled out any kind of tube short. It appears that if the amp is stone
> > cold,
> > there is a slight delay before the buzz and blown fuse event takes place
> > when
> > the HV switch is thrown. Once it is warm, it trips right away. I did some
> > simple troubleshooting, and there appears to be no short of any kind on
> > the
> > HV line (with the Ip meter disconnected, otherwise it gets in the way of
> > checking to ground). The only thing I could not confirm was the two solid
> > state rectifiers. When measuring from the base to the anode, I get an open
> >
> > reading in both directions. Is there a way to test these that I am not
> > aware
> > of?
>
> ::You'd need a "Megger" (which generates substantial voltage to
> measure resistance) to check these...they use a lot of junctions in series
> and have too high a Vf (forward voltage drop) to be measured with a
> conventional VOM that only delivers a few volts to the device being
> measured. However, the fact that they read "open" and not "shorted" would
> seem to indicate these are not what are blowing the fuses!
>
> -WB2WIK/6
>
> >
A small power supply capable of 15 to 20 volts should work to check the diodes.
Put a resistor in series with the diodes and power supply. A 1k resistor should
work fine. Then measure the voltage across the diodes with your vom. Or the
voltage drop across the resistor. Reverse the connections of the diode. In the
reverse direction there should be no current. You now have a high voltage ohm
meter.
73
Gary K4FMX
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