Hi Guys,
Thanks to all for a great time in FISTS C2C this
weekend. If you worked K6FFF #4444 with Don as the op,
that was me. You probably noticed no signs at all of
the PTO instability problem that I posted earlier to
this list about. The rig worked FB for the entire
contest period.
In a nutshell, the problem occurred after tuning from
high to low in the CW portion of the band and after
releasing the main tuning knob, the received signal
would hop up or down by 50 hz or so every few seconds,
then return to center.
In the PTO, the hole in the pistol was excessively
large for the spring rod. With some help from the
list, a new pistol was obtained and installed - along
with a new brass worm just for good measure. This
corrected the problem with "frequency warble" at
certain points of the dial after dialing down.
There was still a small amount of frequency
instability however, at all points of the dial
regardless of whether there was dialing of the main
knob.
One factor was the PTO ground. You should notice that
when you are listening on the Corsair II (CW mode) and
gently lift up the lower cabinet just below the main
tuning knob, the received tone changes. It's not the
speaker magnet affecting the PTO coil as you might
suspect. It's the effect of the lower cabinet and
overall chassis ground on a poorly grounded PTO. Over
time, the ground is greatly compromised on the PTO
upper and lower covers, which are each held in place
by one screw and insulated by a cardboard cutout.
I removed the bottom cover from the PTO and cut away
some of the cardboard that insulates it from the PTO
body. I also removed the cardboard from the top cover
and ran some solder wick from the PTO PCB ground to
the chassis. I used some deOxit on the PTO covers as
well. After doing this, twisting or pressing on the
cabinet anywhere does not change the received
frequency.
The other factor was the accessory connector on the
rear panel. Pressing on this while listening (on CW)
would cause intermittent tone changes on the received
audio as well. I tightened up that connection, used
some deOxit there, and also replaced the small plug
for VFO OUT and VFO IN with a shielded cable. I also
lubed the RX antenna switch which was going open
fairly often.
So far, so good with a stable and smooth tuning PTO.
Thanks to all for your suggestions and help with
parts.
73,
Don Rasmussen WB8YQJ/6 FISTS #6530
Carlsbad, Ca.
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