This is the Harris Radio Section of
The Broadcast Archive
Barry Mishkind - The Eclectic Engineer
Harris 20K tech tips.
Problem: Still fighting with the bad boy 20K. Will only do about
5-6KW at high PS voltage. Ep is normal--about 9K. Ip is about 2 amps at current
output. PA screen voltage is high (around 1200 volts) and adjusting it has no
effect on power, although we are seeing some PA screen current--about 65 ma at
low voltage and 15-20 ma at high voltage. Has new drivers. Found 22 ohm metering
resistor on IPA cathode shorted; replaced--now cathode current is pegged and
when multimeter switch is in IPA cathode position power jumps up by about 2 KW.
Comments: The IPA section is usually where most problems are
with that box. Check each of the IPA cathode bypass caps for physical integrity.
Also check to see if one shorted, and/or if one of the IPA sockets is shorted.
Check the connection between the IPA and PA. Check R36 and R37. Then
inspect the PA socket. Sometimes fingerstock falls down in the socket, and you
have to have really good light and perhaps an inspection mirror to find it, as
it is often tarnished and dark colored. Check for cracked caps.
Also, check the length of the IPA trombone. My experience is
that 99 times out of 100 this causes problems attributable to this particular
transmitter. The weird thing is that the trombone can be the wrong length and
the unit will literally run for years with no apparent problem until one
You get the picture.
By the way, I do not take credit for this discovery. J. Fred Riley taught me
this one (and if you know Fred you 'know Fred').