Houston, We Have a Problem!

The Problem is Linear Amp Switching!


I am fortunate to own three operational Collins KWM-1's, and these are in daily use at N6QW, if only to take a quick listen on 20M. On some rare occasions I even get to hit the PTT. 

At this stage of my life, I think of QRP as 100 watts and so my trusty rebuilt SB-200 is put in the loop to provide 600 watts to the Delta Loop Antenna. I usually get heard! 

One problem I encountered is that my three KWM-1's are not all the same circuitries. I have S/N 5XX, 7XX and 9XX. There were only about 1250 units built so the three represent decidedly different block builds in the production run. 

Only the 9XX unit has a set of relay contacts brought out to one of the pins on the aviation style connector for turning on an external amp. This is pretty straight forward. 

As I found out after a bit of head scratching, the other two do not directly have this feature. But there is a modification that could be done to pick a ground on transmit pin on a relay -- but there is no wiring as such inside those two KWM-1's to do that.

I got a bit "snookered" at first because the manual I had was for the 9XX unit. Tracking down an earlier schematic, I could see why the other units could not turn on the external Linear Amp -- no internal wiring!

So, searching my garage junk box (the whole garage is a junk box), I found a relay, a couple of microphone connectors, an RCA jack and a diode. The schematic is shown below. [I do not want to hear any crap about P Type switching MOSFETS. I found the parts in about three minutes and using a junk hulk of a metal box for a chassis I was in business.]






A couple of lessons learned that include matching the unit S/N to the schematics. Drake had several schematics for the TR-4, and you needed to assure what you were working on was the same as the schematic. Using the external relay box -- any KWM-1 regardless of S/N will work with a linear amplifier.

Another lesson -- the objective was to turn on a linear amp with the engagement of the Microphone PTT. A simple relay works as well as a P Type MOSFET switch. In the OT days --hams used a foot switch to turn on the linear amp. This is a step up.

Mass Shootings over the past several days are simply an unacceptable reality. 


What MTG fails to realize is that some of those affected are card carrying MAGA Republicans. But I guess that is unimportant.

Maybe what we need is more guns on the streets and then the MAGA Republicans will kill off each other. 



73's
Pete, N6QW

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