{Collins} Re: KWS-1 Driver's



Tom
Check the RF choke which feeds negative bias to the grids of the final 
amplifier (4CX-250's). I had the same problem you have on my KWS-1 and was 
perplexed as to why I lost the output of the 6CL6's. The choke's pie 
sections had compressed together over time, as heat had caused the wax to 
soften and allowed the pie sections to merge together. The choke now had 
enough lumped capacitance as to significantly reduce the impedance looking 
into the grid circuit of the finals.

Replacing the choke fixed the problem.

Paul - WB2NMI

  ----- Original Message ----- 
  From: Tom Elmore
  To: collins@xxxxxxxxxxxxx
  Sent: Wednesday, June 20, 2007 3:04 AM
  Subject: {Collins} KWS-1 Driver's



   In the ongoing troubleshooting of my KWS-1 I discovered that R231 the
  screen resistor to the 6CL6 drivers was reading over 5400 ohms instead of
  4700. At this time I was able to clip out the old resistor and temporarily
  substitute a new one in it's place. I finally had grid drive for all of 30
  seconds then poof no more output out of the drivers. I have almost 5 volts
  RF at J-207 and around 600 to 700 milivolts RF at J-201 instead of the 30 
to
  40 volts I saw when I had grid drive and this is on all band positions. I
  have measured plate voltage and screen voltage and they are close to what
  the book calls for. I have swapped out both driver tubes with the same
  results. I have carefully looked to make sure a tube pin wasn't touching
  something it shouldn't be. The only thing I can think of is a cap has 
either
  opened or shorted possibly somewhere?




  Thank You
  Tom Elmore
  Anchorage, Alaska

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 NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific
  SUNDAYS: 14.263 MHz-2000 UTC  +  AM Net: 29.050 MHz-1200 Central
       1st Wednesday AM Net 3.880 MHz-2000 local (ET, CT, MT, PT)





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