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ELECTROLYTIC FILTER CAPACITOR REBUILD
Written by: Al Parker, W8UT
Some pix of the electrolytic cap rebuild for Drake R-4A & R-4B filters.
I cut 4 cans of the proper size (1-3/8 x 3 inch) apart as shown. I used a lathe; it can be done with a razor saw or even a tubing cutter. The insides came right out of one of them. I had to use some heat from a propane torch to slightly soften the inside material (ukumpucky is the term often used). They all came out in one cylindrical "lump," not as a messy goo. The aluminum leads to each section are easily cut to leave the cap with terminals, and the remains disposed of. The cans should be cleaned inside, there's a little residue on the sides. I used kerosene.
The can had 3 sections of 100mf @ 250volts, and 1 section of 22mf @ 250v. Actual voltage in the receivers is below 200v. I used 200v units for the 100's because the supplier was out of stock on 250v caps. I selected units based on their physical size, as I knew space was at a premium.
The 16m diameter is too big to allow 3 caps to be put side-by-side, but the length will allow 2 to be stacked. The negative leads were formed together and soldered with a #20 bare wire, the positive leads had a #20 lead extension soldered on, with shrink tubing placed over them. The terminal end of the can was drilled next to the existing terminals for the #20 leads, as the leads inside the original filter were aluminum, and were staked or welded to the copper terminals. The #20 leads were then solder to the existing terminals, and the negative lead was soldered to the can. A stranded lead was soldered to that point to be later soldered to ground inside the receiver. Epoxy was then used to re-seal the unit.
I hope this will encourage others to do the same. It's not a hard procedure, after the cans are open, less than an hour of work will give a new multi-section filter capacitor.