This is the Harris Radio Section of
The Broadcast Archive

Maintained by:
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 day.....

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').

 

 

 

 

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