[600MRG] WD2XSH/7 is back on the air...

[Ralph Hartwell]

...after some transmitter maintenance.

I found that there was a shorted regulator MOSFET in the grid bias circuit.
This transistor had failed several times before, and after careful
inspection of the circuit, I noticed that when I built it, I had omitted a
protection diode for the MNOSFET. I added the diode, and hopefully that will
correct THAT problem.

The plate current was quite erratic prior to the failure. I discovered that
two of the VR tubes in the screen supply had expired. Instead of regulating
at 150 volts, they were jumping between an open circuit and shorted. I
replaced one of the VR-150's with a spare, and replaced the other VR-150
with a VR-105, which was the only other spare I had on hand. That lets the
regulated screen voltage run about 55 volts low, so the output power is also
slightly lower than normal. However, I can still get enough output to make
the WD2XSH legal power limit. A soon as I get some new VR-150's, I can bring
the screen voltage up to the normal 600 volts.

The 4-400A seems to have survived the transmitter failure OK.

I had not been able to get at the transmitter repairs sooner because I was
quite busy revamping the hamshack/shop/office to make more space for my
business.

WD2XSH/7 is beaconing on 476.300 KHz, 20 watts radiated, with a mix of CW
and PSK31. Scheduled operating hours are 24/7.

73,

Ralph  W5JGV - WD2XSH/7