[Amps] QSK-5PC

[k5jv]

Greetings to all,

        I recently bought a used QSK-5PC from a Ham in Hawaii.  I have never 
used Pin Diode QSK and was a little set back at the complexity of the 
circuit to accomplish such a simple function.

        When I received the board, both fuse laps were burned open.  I 
replaced them with bulbs from Radio Shack and hay-wired board into an 
HL-2200. I used and external supply to provide 12 VDC and tapped off the the 
capacitor string to get 460 VDC for the high voltage bias.  Everything work 
the first time.  It is nice to have absolutely no sound from the QSK, the 
meters just jump up.  I have had no "flashing lights", just good QSK.

        A test was made with a full 1,500 watts, using dits, at about 30 
wpm, for 15 minutes.  I used an inferred/Laser thermometer to monitor the 
temperature of all of the Pin's and switching transistors.  A very slight 
temperature rise was noticed, no more than ten degrees.  However, I did 
notice that the Pins do not increase in temperature evenly.  This makes me 
wonder about the matching of the Pin's or the voltage distribution given by 
the equalizing resistors across the Pins.

        I ran this same 15 minute test again.  This time Varying  the SWR 
throughout the fififteen minute period between 2:1 to to 5:1 (never less 
than 2:1 and 5 minutes at 5:1) monitoring temperatures constantly.   To my 
surprise,  there was very little temperature rise, never more than 15 
degrees.   I turned everything off just long enough to let the capacitors 
bleed down and touched each device with my fingers.  There was no 
noticeable, to the touch, increase in temperature of any device.

        I have been thinking of increasing the back bias by moving the HV 
tap up one capacitor.  In this particular amp, with special Peter Dahl 
transformer, that would result in about 900 VDC.  I really do not see any 
reason for doing this.  The switching transistors are rated a 1,000 V. 
Ameritron offers a cooling fan for their stand alone unit.  Has anyone had a 
problem with temperature rise?

        As I said above, this is my first association with Pin Diode QSK.  I 
would really appreciate any comments that you might have.  I would think 
that the real test would be to loan this amp to one of the local CW contest 
operators and let him work it out over a weekend contest.

73 de Lon, K5JV

281-358-4207