[Hallicrafters] SX-100 tuning

[Roy Morgan]

On Feb 22, 2015, at 4:53 PM, Gerry Steffens <gsteffens at bevcomm.net> wrote:

> I have 4 different SX-100s. ...
> All of these SX-100s are a little sluggish or more so in the mechanicals of tuning. ... If one serviced the gearing, do these radios perform as some others, needing almost no effort in tuning and coasting down the dial given a sharp twirl?

Gary,

Yes, almost certainly they will behave differently after a complete strip down, cleaning, and re-lubrication.

Some years ago I had the interesting experience of completely rebuilding an SX-88.  Those radios were worth some two to three thousand dollars then, so it was worth the trouble to do it right from end to end.

As received, the radio worked ok mechanically but was a bit sluggish as you mentioned.  It has two complete independent gear trains, with anti-backlash gear sets throughout each train.  I completely dis-assembled both gear trains, down to the bell bearings wherever I found them.  After very careful cleaning, lubrication, and re-assembly the thing was a whole new radio.  A modest twist of the knob would send the dial coasting pretty much from end to end of its travel.  Backlash was reduced to zero, which is amazing considering all the gearing involved.  The slightest movement of the tuning knob would bring an appropriate change in pitch of a BFO note.

That whole process is not for the faint of heart or the impatient worker.  You can lose bearings, forget which gears go where, and make goofs in setting the backlash spring tension in the anti-baklash gear sets.  But it was worth it!

I m not familiar with the SX-100 gearing, but I suspect at least some of the same mechanisms will be found in there.  If you decide to tackle the  job, I will be glad to share some tricks I learned to help get the gear loading right without tearing your hair out.

Roy

Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958