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12th Mar 2005, 10:02 am | #1 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,289
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Repairing Broken Trimmer Capacitors.
When I attempted to realign my Wartime Civilian Receiver I found that adjusting the trimmer capacitors made no difference to the response. A closer look showed that the moving plates had snapped off in the centre of the "U" bend where stress is greatest.
I carefully removed the moving plates, taking care not to lose the insulating washers/dielectric. The brass on either side of the break was cleaned by gentle scraping and some solder flux applied. The brass was then tinned with solder. The trimmers were then reassembled with a wedge of paper between the plates. With the two halves of the breaks carefully aligned the adjusting screws were tightened to hold eveything in place. The joints were then quickly soldered with a large iron. It took a couple of attempts to get things just right. The plates must have some spring holding them apart and the holes in the plates must be concentric with the adjusting screws to prevent short circuits. I am pleased to say that the repair was 100% successful and saved me from having to replace the trimmers which are an integral part of the main tuning capacitor. Graham. |
22nd May 2005, 4:07 pm | #2 |
Retired Dormant Member
Join Date: Apr 2003
Location: Salt Spring Island, BC, Canada
Posts: 368
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Re: Repairing Broken Trimmer Capacitors.
I had a problem with the trimmers on a BC384, also with similar trimmers on the RBC, RBB, RBA receivers. The difficulty was that the interference fit collar on the shaft had become lose and the moving plates had drifted over and shorted to the fixed plates. The solution was to reset the plates spacing and set the collar in the correct position, then drill a small hole completely through the collar and the shaft and pin them using a fine finishing nail. The nail ends hanging out were clipped short and filed smooth. The nail surface was roughed up in the jaws of pliers to give a tight friction fit. The hole drilled should be no bigger than one third the shaft diameter.
John. |