Heathkit Apache TX-1

Michael Waldrop w5rkl at YAHOO.COM
Sun Sep 2 00:44:41 EDT 2007

I am wondering if there is anyone who has experienced a modulation
transformer failure in a Heathkit Apache TX-1? What symptoms did you
experience prior to the transformer failing?

My Apache, in transmit, has a noice that appears to be a very short arc
that sounds like a "tick" noise that can be heard by standing in front of
the transmitter. The sound appears to be loudest at the left front. The
modulation transformer appears to be warmer than normal. When the sound
occurs the mod idle current drops to zero but returns to 50ma or there
bouts. The mod idle current does increase to around 60ma when keyed
with no modulation.

I've changed the 100uf modulator biasing filter cap plus the diode and
cleaned the pot but the problem is still there. The pot does adjust the
mod idle current when set to 50ma. I've even changed the pot to a new
pot and the problem still occurs. The mod tubes are EL-34/6CA7's from
"Harmonic", purchased them from Fair Radio Sales.

The modulation is good and clean when the problem is not occuring. I'm
stumped. I am leaning towards arcing in the final or one of the 5R4GY
recitifier tubes. The recitifer tubes are at the left rear which, if
the tubes are arcing, would seem the noise is heard the loudest at the
left front.

Unfortunately, I don't have a spare 5R4GY recitifer tube so I can't
determine if it is the tube or not. The tube does show questionable
on the tube tester even though the tube tester doesn't apply 750VDC
and test at 225ma to the tube during test.

Mike W5RKL

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