[Boatanchors] Reforming caps

[jeremy-ca]

Glad to hear that Barrie; I like that 40 ua reading.

By chance do you have the date codes of those caps?

My tester is a late 40's era 500V @ 200 ma variable and regulated lab supply 
that I rescued from near dumpster duty about 30 years ago. Ive modified so 
that I can use as original or as a reformer. In the latter Im using a 100 ua 
meter with switched shunts mounted on top of the PS, havent blown the meter 
yet!

Its also a great supply for setting up and testing old free running 
breadboard "yooper" transmitters. Amazing how stable they can be with 
regulated B+ and filament voltages.

Carl
KM1H



----- Original Message ----- 
From: "Barrie Smith" <barrie at centric.net>
To: <boatanchors at mailman.qth.net>
Sent: Saturday, May 24, 2008 6:53 PM
Subject: Re: [Boatanchors] Reforming caps


> I'd like to thank everyone that answered my question regarding reforming 
> caps.
>
> I finally got four done with my terrible old lashup.  All drew less than 
> 40 microamps at close to full rated voltage, so I's say they are still 
> good.
>
> This contraption that I built for the purpose, probably twenty years ago, 
> certainly needs some re-engineering!
>
> For starters, the voltage is read on the output side of the 
> current-limiting resistor, which must be a very high value, ohms-wise, 
> because the voltage at the cap rises very, very slowly.  At one point last 
> evening I came back to see 450 volts on a 400 volt cap.
>
> I'll install a switch so that I can set the voltage on the input side of 
> the current-limiting resistor first.  Then I can set the switch to monitor 
> the actual voltage on the cap.
>
> Anothe real problem is that when I'm finished with a cap it's 
> fully-charged. The only way it's going to discharge is back through the 
> high-value current-limiting resistor, which takes 2 hours to go from 400 
> volts to 175 volts.
>
> I need yet another switch so that when I'm finished, and the tester power 
> supply is shut off, I can switch a 5000 ohm resistor into the circuit to 
> act as a more rapid bleeder.
>
> Again, thanks!
>
> 73, Barrie, W7ALW
>
> _______________________________________________
>