Richard, Any readily detectable leakage is too much for a grid coupling cap IMO. A cap that even partially closes the eye on the 1uA setting of my Heathkit is grounds for replacement. Modern caps are cheap and easy to obtain. If you don't like the bright colors of new axial caps, just slip a little heat shrink over them and "viola" you have a mini black beauty :-)
Dennis AE6C On Sun, Apr 3, 2011 at 5:43 AM, Richard Knoppow <1oldle...@ix.netcom.com>wrote: > > -----Original Message----- > From: Dennis Monticelli > Sent: Apr 3, 2011 1:22 AM > To: Richard Knoppow <1oldle...@ix.netcom.com> > Cc: Drake List > Subject: Re: [Drakelist] Testing Caps for Leakage > > Richard, > > That is very true. Paper caps can leak yet look OK for capacitance and not > too bad for ESR. I think 5uA is too high for a paper cap. If that cap is > being used for plate to grid coupling and the grid circuit is 1 Mohm, there > will obviously be a problem. > > I have a common Heathkit IT-11 cap tester and I've calibrated the eye > closures for 1uA/10uA/1mA respectively on the leakage switch. It tests caps > just fine and will form electrolytics. > > Dennis AE6C > > I don't remember where I got the 5 uA value, you could well be right. > It doesn't take much leakage to cause problems with coupling caps. Modern > film caps have leakage so low its difficult to detect. > > >
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