Heathkit Apache TX-1

Michael Waldrop w5rkl at YAHOO.COM
Sat Sep 8 10:34:59 EDT 2007

Thanks to everyone for their suggestions.

The ticking noise ended up being a bad final B+ .001ufd 2KV mica bypass
capacitor. The original cap located on the left wall of the final cage
and at the base of RFC L16, appears to have been arcing internally. Replaced
it with a new .001ufd 6KV disc cap. I no longer hear the ticking sound
in transmit.

The erratic modulator plate current was caused by the rear panel DPDT
relay. The contacts were dirty but even after cleaning them, the problem
was still there. It turned out the contact used to switch the EL-34's
screen voltage was loose in the support. This was probably caused by
applying too much heat to the contact either by the original builder or
a previous owner. Since the other set of contacts is wire to the 2 rear
screw terminals, most likely for receiver muting, I simply swapped contacts.
The EL-34's idling plate current is now quite stable at 50ma with no

The original specification state 150 watts input on AM fone. With 6ma of
grid drive, 750VDC on the finals, and a resonant plate current of 210ma,
that's 157.5 watts input. The output is 120 watts on 75 meters into a
dummy load or my G5RV. That's about 70% efficiency, not bad for a 48 year
old transmitter. I have replaced all the power supply electrolytics before
any testing (no NOS caps, only new caps).

Mike W5RKL

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