Although I have a later digital transceiver (Icom-751), I recently acquired a
Swan-500-C from an estate. It had been in storage for 25 years. I have had fun
working on it's quirks and returning it to very good performance, even by
today's standards:
The first quirk was not staying on frequency (not related to time/heat drift).
Slightly wiggling the bandswith knob caused slight changes in voice pitch. And
what was worse (and intolerable in a group discussion) was that often Transmit
on a slightly different frequency than it received on. A change of more than
100 Hz or so is usually intolerable.
My initial thought was oxidized bandswith contacts. I bought some "Deoxit" at
Radio Shack dowsed all the contacts except the ones in the VFO compartment. This
may have helped slightly but problem was essentially the same. Then I "Deoxed"
the bandswitch contacts in the VFO compartment which I SHOULD NOT HAVE DONE,
because the material is a different plastic and was severely affected. It changed
the frequencies by more than 30 KHz...probably by changing the dielectric constant
of the plastic material. I quickly rinsed this off with FREON-TF and frequencies
returned almost to where they were before.
The original problem still mostly existed after all the contact cleaning. I had
even used "PB-Blaster" rust solvent from Auto-Zone on the main bandswitch (not the
VFO) which made no noticeable difference. I finally flushed all the contact
cleaners back off with FREON-TF which pretty pretty much leaves them clean and dry.
HERE'S WHAT SEEMS TO HAVE BEEN THE MOST SIGNIFICANT "REAL" PROBLEM:
While trouble-shooting the problem, I monitored the actual VFO frequency (which is
always the operating frequency plus or minus 5500 KHz in "Normal" sideband), with
my Icom-751 listening as a frequency-meter:
I found that tightening, or loosening the mechanical linkage between the two
band-switches (VFO and lower gang), the "pitch" of tone I was listening to on
the Icom changed by about the same 100 or 200 Hz as exhibited in the origanal
problem. The long band-switch shaft passes through several wafer sections and
is only grounded near the knob and de-tent assembly which provides a poor and
un-reliable ground. (Slightly wiggling the band-switch knob always caused a
significant change in the tone pitch I was monitoring).
Apparently, when the shaft was not firmly grounded, it provided a capacitive-
coupling path between certain wafers that caused the problem.
AS A CURE, I soldered a flexible jumper (Pig-tail) between the lower shaft and
chassis ground, and also a jumper on the larger section of the mechanical linkage
above the chassis to ground.
On a different aspect of improving the SWAN-500 performance, I used and external
wall-receptacle-mounted transformer to light a 12 volt auto tail/stop light and
placed it against the VFO compartment to simulate heat when the transceiver has
been on for awhile. Although probably not necessary, I took the opportunity to
negative-rectify this 12 volts and send it in one of the accessory socket pins (I
don't have the pin# handy, but it goes the 25W 10-volt zener(-10v) mounted under the
chassis. You may have to limit the current to the zener with a resistor if your
voltage is excessive. This keeps the transistorized VFO section running at all times.
I have found that remarkably, there is virtually no warm-up time required for
SSB standards operation...comparable to the digital frequency-synthesized more
modern transceivers. Of course you disconnect the external heat while operating
the transceiver.
If better voice quality is your preference, the SWAN provides this by using a
wider crystal-filter band-pass of 2.7 KHz which is noticeably better than the
Icom-751 which is 2.3 KHz bandwidth, and some transceivers even use 2.1 KHz.