Al,
My SP-600 has both problems....slippage AND backlash.
I did see how the brass on brass friction drive is done at the
tapered brass wheels and the dials. I tried everything to eliminate
the slippage, and was 95% succesful.

I've come to the conclusion that this radio has been used a LOT,
and is just showing signs of excessive wear. The front panel
had never been off, so I'm sure the bearing at the front of
the tuning cap is still there, but I'll bet its corroded to some
degree. Everything else on this radio was. I even replaced
most of the screws because they were so rusty. I'll pull out
the bearing tomorrow and take a look.

The tuning mechanism on the SP-600 is normally silky smooth,
and certainly one of the reasons I've always enjoyed using them
over the years.

Thanks very much for your note and suggestions!

Steve


"Al Parker" wrote in message
...
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

"Steve" wrote in message
...
Al,
My SP-600 has both problems....slippage AND backlash.
I did see how the brass on brass friction drive is done at
the
tapered brass wheels and the dials. I tried everything to
eliminate
the slippage, and was 95% succesful.

I've come to the conclusion that this radio has been used
a LOT,
and is just showing signs of excessive wear. The front
panel
had never been off, so I'm sure the bearing at the front
of
the tuning cap is still there, but I'll bet its corroded
to some
degree. Everything else on this radio was. I even replaced
most of the screws because they were so rusty. I'll pull
out
the bearing tomorrow and take a look.

The tuning mechanism on the SP-600 is normally silky
smooth,
and certainly one of the reasons I've always enjoyed using
them
over the years.

Thanks very much for your note and suggestions!

Steve

Another although unlikely possibility is that the clamp
for the bandspread dial, which drives the rest of the
mechinism, is not tight. The symptom is that the logging
dial turns but the main dial does not. That doesn't sound
like what you describe.
The times I've had slippage have all been caused by
residue of some sort on the edge of the logging dial and the
friction wheels which drive it, they must be absolutely
clean and dry.
I've also seen one case where the movement of the spring
loaded "spiders" was limited because of MFP compound, the
spiders must move very freely.
There is a pretty extensive handbook showing the gear
mechanism on the BAMA site. It should be absolutely buttery
smooth.


--
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Richard Knoppow
Los Angeles, CA, USA