[Hammarlund] SP-600 Tuning

[James A. (Andy) Moorer]

This is a classic one. The problem with either one of your proposed
solutions is that it acts as a "brake" and slows down the spinning of the
big, brass wheel. This makes it harder to cruise from one end of the tuning
range to the other. There are a couple of things to look at:

Most of the time, the problem is that the little coupling wheel that is
between the vernier disk and the big brass wheel doesn't slide properly.
There is a spring that looks like the letter "S" that holds a triangular
carriage that holds the coupling wheel tight against the other two. That
carriage needs to slide smoothly. Any dirt or grit underneath the little
carriage will keep it from engaging properly. The other thing to do is to
stretch the S-spring out a bit so it applies a bit more force. Be careful
not to bend it too far or it will lose its springy-ness.

If worst comes to worst and it just won't engage, go to the local music
store and get a block of violinist's rosin (they will ask you what kind -
just get the cheapest "student" one). Apply some rosin to the outside of the
vernier and to the outer edges of the coupling wheel. If they touch at all,
this will allow them to grab. The only drawback of this solution is that it
produces odd behavior at the end of the dial - the vernier wheel will
"shudder" as you try to move it against the stop instead of slipping
smoothly. Plus, bits of rosin flake off the wheels for a while after you
apply it. I have no idea what the long-term behavior of the rosin is. I hope
it doesn't do anything bad.

Let us know what happens.

James A. (Andy) Moorer
www.jamminpower.com

----- Original Message -----

> GE List.  I am restoring a SP-600 JX-17.  I now have the radio working
> electronically but am having trouble with the mechanics.  The fly wheel
> slips that is part of my main tuning.  I have two solutions:
>
> 1.  I could paint one of the brass mating surfaces with a rubber type
paint.
> 2.  I could put a rubber "O" ring on the main fly wheel to cause some
> fricton between the two surfaces.
>