[Heath] SB-104A squirrely VFO?

[JF]

On 3/18/2016 3:47 PM, Alexander N. Gerli wrote:
> This happened to my last '104A. The VFO tunes in a wobbly manner, 
> skipping here and there. I remember pulling the VFO Assy and 
> opening it, then cleaning the wiper on the rotor shaft that 
> contacts the stator. I guess that lube or something gets in there 
> over the years and causes poor contact. The job's a bit of a pain, 
> but cleaning takes care of the skipping.
> Anyone else experience this? I've never built a '104 from scratch, 
> so I guess the VFO Assy is pre-assembled.
> 73,  Sandy AC1Y

No, the SB-104A VFO was not pre-assembled. The twitchiness in an aged 
VFO is due to the shaft bearings eventually not making good contact 
with the frame - I seem to recall that there was a conductive grease 
in the bearings that dried out with time. The best fix was to solder 
a length of very flexible copper braid (like RG58 coax braid) from a 
clear spot on the shaft to a nearby chassis ground point. The trick 
is that you have to install it in enough of a spiral so that when the 
shaft is turned to the stops it does not pull the braid tight or bend 
the braid at the solder point.

Other wire/cable connector ground points may need to be re-soldered.

Another responder to your post recommended a URL for a tutorial for 
tube-type VFOs, and the process is similar to that for the 
solid-state VFO; however, there is one statement in it that is, IMHO, 
potentially wrong  - it says you can use tinned or untinned braid, 
but if the tinned stuff is stiff at all it will not flex well enough 
to last.

73
John  KE5ZB