[Amps] Testing 8874s

[rgroh at swbell.net]

Barrie,

There have a number of nice sources for information on hi-potting tubes etc. Here is one that addresses your question rather nicely:
http://www.nd2x.net/k8cu-HV-tester.html

73
Bob, WA2CKY

----- Original Message ----
From: "wa4tuk-rf at comcast.net" <wa4tuk-rf at comcast.net>
To: Barrie Smith <barrie at centric.net>; jeremy-ca <km1h at jeremy.mv.com>; Steve Thompson <g8gsq at eltac.co.uk>; amps at contesting.com
Sent: Friday, November 2, 2007 2:27:41 PM
Subject: Re: [Amps] Testing 8874s


I would also be interested in guidelines for tube leakage using a
 hi-pot tester.  My homemade unit will go to 10kv DC and I've used it to test
 some long stored tubes for leakage but interpretation of the results
 is only a guess. Metering is plus or minus 50 microamps.

At what voltage do you test? At 2 times intended DC plate volts or
 maybe 4 times DC plate volts? Test between plate and grid?

How high can the leakage be before the tube is unusable? How do you
 predict where it might flashover?

How much leakage condemns a vacuum variable to the trash? 

The types in question are the typical kinds a  ham might use 3-500,
 4-400, 811, 813, 572b, etc.

FYI, there is an article that Eimac (CPI) publishes on hi-pot testing
 of tubes. It is directed at very large tubes that need conditioning
 before use. One concept they talk about is de-barnacleing new tubes to
 flash away high points within the tube by controlled flashover.

One surprising finding was how well my old collection of 5r4's fared
 and how well 1n4007's actually tested.  (They tested well above 1kv
 before they even though about reverse flow.)

Pat
wa4tuk


 -------------- Original message ----------------------
From: "Barrie Smith" <barrie at centric.net>
> 
> 
> 
> > Highpot wouldnt hurt. I didnt mention it since it is not a common
 ham
> shack
> > item. The one I built around a sign transformer goes up to 13 kV.
> >
> > Carl
> > KM1H
> >
> I have a high-pot tester that I've used for testing vacuum caps.  I'd
 like
> to use it to test various, mostly glass, tubes, as well.  However, I
 don't
> have a clue as to what the voltage used should be, nor what would be
> acceptable leakage; or, between which electrodes.
> 
> I've googled for information, but have come up short.
> 
> Are there any rough guidlines for hipoting glass transmitting tubes?
> 
> Barrie, W7ALW
> 
> 
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