[Amps] Hi-pot testing

[John Lyles]

What sort of current can your hi potter provide in an arc? Depending on 
the energy it dumps, you might be careful when raising voltage above the 
ratings of parts. I would not risk running capacitors or wiring, 
rectifiers, above their rating. If they are vacuum capacitors you can 
get away with higher. For tubes, you should be able to test them above 
rating. Most of the ratings are for circuit operation, and in AM it is 
much lower than it is for FM/CW, due to the modulation peaks. But high 
potting a tube out of the amplifier circuit, should allow running them a 
few kV above the datasheet operating maximums noted above. I high pot a 
tube that runs at 15 kV, at 20-25 kV typically when new. With a high 
potter than can only run a few mA, the risk of damage due to an internal 
arc is low, if the high potter can shut off quickly. When I hi pot a 
tube and it does breakdown internally, it just tics the current meter 
and clicks off the high potter. This is benign for tubes, unless you 
have a nasty flash arc over the outside of the tube in air and the high 
potter says on.

73

John

K5PRO

> Date: Fri, 12 Feb 2021 17:39:46 -0500
> From: Steve Bookout<steve at nr4m.com>
> To:Amps at contesting.com
> Subject: [Amps] Hi-pot testing
>
> Hello all,
>
> Several months ago, I had a problem with a 40 year old HB amp for 160.?
> Just sitting there, it started making an arcing noise (sort of) and
> showed plate current jumping around.
>
> Now, I'm finally looking into it.? I'm using a HB hi-pot tester and am
> testing pieces and parts up to their voltage rating.? FYI, the plate
> voltage is 4 KV and most things are rated much higher.?? I was checking
> things out at 5 to 6 KV with very minimal current showing.? Happy with
> that.
>
> Question:? Someone once told me that new Eimac tubes were tested at
> twice their rated voltage.? Ok, fine.? What about capacitors????
> So, what should it test if it were brand new?
>