[Heath] SB-104A VFO question

[G3OOU at aol.com]

Hi Sandy
 
My SB104A that I recently sold had a conventional VFO and frequency counter 
 to display the operational frequency. I suspect that your frequency  
jumping is either a problem in the slow motion drive mechanism or the  
lubrication in the VFO tuning capacitor sliding contacts has dried out - the  latter 
is a well known problem in earlier valve SB-Line models (which run a lot  
warmer than the '104A). Also, take a look to ensure that the grub screws and  
fixings have not come loose in the drive mechanism or VFO mountings.
 
Another quick test is to spray a little switch cleaner lubricant onto the  
sliding contacts and bearings of the VFO tuning capacitor and see if that  
fixes the problem in the short term - use it sparingly though. If that  works 
you may have to clean and re-lubricate the capacitor contacts and bearings  
but well worth the effort.
 
While you have the VFO open, check that the sliding contact springs have  
some tension by pressing gently down to feel the tension and see that  they 
return to their original position.
 
I have seen recommendations to solder a piece of braiding between the rotor 
 and the body of the tuning capacitor on some SB models but I have never 
had to  do that.
 
73

Bob

Bob F Burns
C Eng,  FIET, MSE
Amateur Radio Callsign: G3OOU
Registered RSGB  Instructor
G-QRP Member No: 6907; Zone: 14, QRA: IO91WH; WAB:  TQ25
Secretary of Crystal Palace Radio & Electronics Club: _www.g3oou.co.uk_ 
(http://www.g3oou.co.uk/) 
Technical web site: _www.qsl.net/g3oou_ (http://www.qsl.net/g3oou) 
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