Christopher Hall wrote:
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.

Measure the plate, grid, and cathode voltages with a meter. Compare with
the manual. Work back from there.

A failed tube is entirely possible. Inspect it for internal damage.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."