[AMRadio] Tranny Test


Gary Schafer garyschafer at comcast.net
Mon Feb 19 15:48:04 EST 2007


You had best have something to protect that microameter when you turn on the
supply as the capacitance of the transformer windings will look like a short
to the meter until the charge equalizes.
Running it up with a variac would be ok.

73
Gary  K4FMX

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of John Lawson
> Sent: Monday, February 19, 2007 3:38 PM
> To: Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] Tranny Test
> 
> 
> 
> 
>    Re: quasi-pseudo hi-pot testing of your transformer - if you have a
> device that produces the required 800-1000 VDC - and can access that
> voltage (such as a bench supply, one of the other power supplies in the
> transmitter - or even a Ranger maybe) then [carefully!] attach the
> positive lead of that source to the windings (tie the leads toggether)
> thru a suitable microammeter and ground the tranny frame...  any leakage
> will show up on the microammeter. A panel-mount 0-20 uA DC meter, mounted
> on a piece of plastic, will do.
> 
>    If you use a DVM - just insulate it well - put it in series - don't let
> any part of it get near ground or you - set the meter, step back - turn on
> the HV - check the reading.  Shouldn't be very many microamps to ground.
> Note that any significant ripple, or other AC disturbances, in the HV
> source, will confuse the reading, due to capacitive and inductive coupling
> of those components.  Use 'pure' DC.
> 
>    Remember to tie the transformer HV leads together - the object is to
> measure any current flow from the body of the windings, thru the
> insulation, to the frame - NOT from one side of the winding to the other -
> which would only be a few ohms DC resistance.
> 
> 
>      Cheers
> 
> John
> KB6SCO
> DM09fg
> 
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