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
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