On 04/11/2011 03:37 PM, Christopher Hall wrote:
Thanks to all who have posted regarding this issue, its been a lot of help.
I checked the HV to plate circuit and found a blown (actually totally
destroyed) wire wound resistor in series between the filter board and the
plate choke. The manual and schematic doesnt show this resistor as part of
the kit, so Im assuming it was a mod done by the original owner. I suspect
it may be there to lower the voltage on the plate to extend tube life or to
provide some safety a la Eds post regarding a RF choke to provide some sort
of fuse. The problem is the resistor is so damaged that there are no values
printed on it. Does anyone have any ideas as to what that resistors values
would be?

Thanks
Chris

"Christopher wrote in message
...
I am the second owner of a Heathkit SB-1000 that was built in the late
1980s. It was working great until I accidentally tried to tune it into a
mistuned antenna and I saw a flash through the ventilation screen on the
left side somewhere around the rectifier/filter section and there is now no
power output. The amp powers up, the fan runs, the meter lamps light and
the tube lights up. The amps multimeter shows 3400 volts on the high
voltage position (a little high maybe but it has always been like that).
With no drive, when the amp is keyed there is no plate current and no grid
current. Keyed with drive there is grid current, but no plate current and
no power output. These conditions are the same regardless of which band the
amp is set to. I had thought that the zener diode might have failed so I
replaced it, but nothing has changed. I would appreciate any thoughts as to
what may be the problem and how to fix it.

73
Chris
VE9ZX



I'm betting that resistor (wire wound) was self resonant at the
frequency you were operating on, that's why it exploded. I would just
leave it out for now. If you DO replace the resistor make sure to use a
none inductive resistor and/or bypass it on the HOT end with a suitable
HV capacitor having of at least .001 uf.