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Old 22nd May 2021, 10:58 am   #1
Malcolm G6ANZ
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Join Date: Feb 2006
Location: Bristol, UK.
Posts: 1,030
Default lash up cap reformer

Onward with the GEC. The smoothing caps are defiantly not the original as they are mounted in clips. The date on one of them is Aug 1948, since the radio is from 1938 these must be a replacement. The caps are mounted with the positive terminals uppermost and a wire leading through the chassis. As they looked in a bad state I decided to restuff them. My efforts at this on the first one were disappointing, the resultant mess of the can was not good. Normally this is hidden by the mounting clips but in this case it would be open to sight. I now thought about reforming the rest of them. A clean of the end revealed no surprises, no bulges or leaks.
I have a Radford Lab Pack which gives 250v at 200mA which I could use as the HT supply. That and a couple of meters and presto a reformer. Before connecting it up to the cap I measured the HT from the pack. Unloaded this was around 300v which I thought to be too high for a gentle reform. So I ran the PSU from a Variac. This allowed the HT to be brought up slowly from 0v to 270v while monitoring the capacitor leakage current.
The first one I tried was a dual 16uF and 8uF. With the 16uF side the leakage was 5mA at 50v which fell to 1mA quite rapidly. Then I slowly increased to voltage to 250 while watching the current. After a few hours the leakage was below 1mA at 250 v. The same process was done with the 8uF side with the same result. Final leakage below 1mA at 250v.
It seems that this cap has recovered from a dormant state and is useable. On to the next.

Malcolm
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