>I am currently gathering components for a new amp project, and
>would like to 'pre-qualify' my parts with a hi-pot assure that the
>proverbial "one bad apple" doesn't blow up the whole bunch
>when I apply HV power.
>
>So, I am considering a simple hi-pot project using a small variac, a
>7.5 kvac 30 ma neon transformer, 15kv rectifiers, .
** 7.5kV-rms produces 21,6k PIV in a halfwave rectifier circuit. I
would go with c. a 30k-PIV rectifier. Also, with a halfwave rectifier,
a 120v MOV should be connected across the primary winding to preclude
rectifier failure. If a FWD or FWB circuit is used, the MOV is not
needed. A FWD would be useful for checking the 15kV vacuum caps that
are commonly used in Ham amps. For 60-Hz mains, 2, 0.01uF capacitors
are suitable for use in a FWD high-pot tester.
>1 mfd 10 kv cap,
>15KV HV 'tigerstripe' resistors and associated components to get an
>adjustable output of about 0-10 kv.
>
>My current "Draft" design would limit direct-short current to 100
>microamps max at 10KV and proportionately less as the adjusted
>voltage is less (50 microamps at 5 kvdc and so on).
>
>However, I have been looking at commercial hi-pots and many have
>adjustable "trip" values of from 1 to 50 milliamps or so, so I am
>concerned that my current designed limit of 50 microamps at 5 KV
>might be too low.
>
** 50uA is plenty, even to do the Funderberg gold-sputter test.
>Can anyone experienced in this area tell me what amount of leakage
>current would be considered "acceptable" or "typical" for components
>such as vac variables
** When you see 1uA of leakage, the breakdown point close. When you
hear a "tink", you have arrived.
>, large tubes,
** >10uA suggests that all is not well.
>RF caps, HV power tranformer
>insulation and the like?
** For ceramic caps, I check 'em at the rated-V. Going to the
breakdown-V causes a short. .
>
cheers, Jim
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