hi Steve,
I'm not sure if you mean backlash, or slippage. The SP-600 doesn't
use the split gears mentioned by someone, as you know.
Are you sure you haven't lost the small ball bearing that is used at
the front of the shaft in front of the main tuning cap, loaded by the
adjustment just outside the steel plate? The tuning capacitor should have
almost no friction, little force is normally needed to turn it, but if
that ball is missing, you'll have lots of friction, and things will
exhibit backlash.
If it's slippage, that more closely fits your description of moving
plate, S-spring, etc. Is it at the brass "wheels" behind the main tuning
knob? If they are bieng held in good contact my the spring, they must
still be absolutely clean. No oil needs to be used on any of the gearing,
it's brass and self lubricating. These 2 "wheels", the small one fits in
a groove on the larger one, work by friction. If there's slippage, clean
them scrupulously with alcohol and a very clean rag. Do not try any
lubricants in that area, or try as some have, to use tape or rubber to
make them sticky.
I have worked on well over a dozen SP-600's in the past few years, and
never have had to do anything other than cleaning to eliminate slippage.
You might try looking at some of the SP-600 refurb/rebuilds that are
well documented on The Hammarlund Historian website,
http://www.hammarlund.info or at some of my own work shown on my own
site, http://www.boatanchors.org
I know I've taken pix of the friction drive mechanism, but not sure
I've gotten them posted on either site.
I hope one of these suggestions helps solve your problem. Let me
know if I can help in any way.
(knobs are rarities, particularly the main tuning/bandchange ones,
they get the skirts broken too easily).
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.boatanchors.org
http://www.hammarlund.info

"Steve" wrote in message
...
A while back I posted about the 'SP-600 from hell'.
After a lot of work, and some great advice, the restoration
is complete. Still a couple of small bugs to work out.

One is bad backlash in the main tuning dial. This
radio uses gears that are mounted on movable plates
that are pre-loaded with an "S" shaped spring. I've made
certain that the plates are able to move freely, and the springs
are OK. Has anyone had, and solved this problem? If
so, I'd sure like to hear from you. At this point I'm stumped.

TIA

Steve
p.s.-still looking for the main tuning and crystal phasing knobs