[Hallicrafters] SX-111 tuning

[Fred Olsen]

Bill Gerhold wrote:
> My SX-111 has developed a tuning problem, mechanical in nature.

Bill, I have no specific knowledge of the SX-111.  That's the caveat.

The drive as you describe it is very similar to the 'edge drive 
verniers' used in various test equipment, notably things like the H-P 
200 series oscillators.  Those I do know.  Rather than add tension I 
would suggest that you first back it off all the way, fully disengaged, 
and check the tuning shaft for rotational stiffness.  You may find that 
the lube in the tuning gang and/or that in any support bushings has 
oxidized to the point that it's stiff and causing the shaft to bind.

The cure is to completely clean out all old lubricants and start over 
with fresh as appropriate.  Once the tuning is as free and smooth as 
possible the vernier should need only modest tension to drive it, 
assuming no worn-out parts.  If the tuning gang is supported in bushings 
or isolation grommets (again, don't know about the 111) make sure that 
nothing has sagged or taken a set such that the shaft is out of line 
with panel bearings and the like.  These things should be as smooth as 
butter when set up and lubed correctly.  The lube on a slide rule 
indicator and its rail can also get very stiff with age.

Good luck with it,
Fred
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