In article .com,
Ed Clark WD4ED m wrote:

Did you ever get this figured out? I have exactly the same amp with the exact
same problem.

Since that's a fairly old posting you may not get a direct response.

Looking at the thread in the archives: it was suggested that this
symptom probably means that there's a fried component, between the HV
filter board, and the tube anode. According to the schematic I see,
the red wire from the filter board goes to a small bypass cap to
ground and into a choke (RFC3). From the output of the choke, it goes
to the anode/plate of the tube via what shows on the schematic as a
resistor (100 ohm 2 watt?) in parallel with a choke or coil of some
sort. At a guess, this may be a "coil wound on resistor" parasitic
suppressor. There's also a connection at this point to the HV
blocking caps and then out to the output-match circuit.

If the choke (RFC3) or this coil/resistor combination is burned or
damaged, it would prevent the tube from receiving any high voltage.
This wouldn't be apparent from the meter reading (since the meter
pickoff is on the HV filter board) but you'd see no plate current
being drawn. Careful inspection of this current path should show you
where the continuity ceases to exist ...

.... IF YOU DO THE INSPECTION WITH PROPER CARE AND PRECAUTIONS. This
is a DANGEROUS high-voltage part of the circuit, and contact with it
while it still holds charge can leave you dead, dead, dead in very
short order.

For what it's worth, I understand that Ameritron offers a professional
repair service for this amplifier (it's a "licensed copy" kit version
of the Ameritron AL80A, designed by W8JI).

See http://www.ameritron.com/heathkit.php for details.