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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.  

  • 100mf @ 200v, Nichicon brand, are 16mm dia. x 31mm high

  • 22mf @ 250v, Nichicon (or Vishay) brand, are 12.5mm diameter. x 25mm high

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.