[NJARC] Megohms in primary?

[Poli, Louis C (Lou)]

Stephen; 
I wanted to comment on the filter capacitors too. Somehow, during your tests now/later, you may charge them. They will try to kill you too.
  Make up now, a shorting stick just the right size to short the caps directly. Use it every time you turn power off, regardless if you think they could have charged or not. Of course check that the installed bleeder resistor is OK but we don't trust it anyway. It will back you up during these experiments.
 I assume the caps are the heavy sealed oil filled type. Chances are they are OK, but you need to watch them too. But one thing at a time.

Remember that the common variac that you may get your hands on, may only handle a few amps. Its OK as long as you don't pull any true load through the power supply. Convince yourself that during your tests, the filament power and basic running of the idle supply will not pull more than the variac can handle for now.

Also forget the one hand in the pocket routine. You can never touch a live lead. Try to ground the rack and chassis to your power ground system, in case the chassis becomes live.

Louis

-----Original Message-----
From: njarc-bounces at mailman.qth.net [mailto:njarc-bounces at mailman.qth.net] On Behalf Of Poli, Louis C (Lou)
Sent: Thursday, November 11, 2004 2:00 PM
To: New Jersey Antique Radio Club
Subject: RE: [NJARC] Megohms in primary?


Stephen;
 Maybe. Its still pretty good. Its  time test it if your sure that the primary wiring is not obviously bad.  Pull out the rectifiers. Note their condition and position. 

 Put a 100 watt bulb in series with xformer. 
  This will take load in case of catastrophic short. Get a variac and carefully bring up xformer through the series 100 watt bulb. Monitor voltage on output and if possible, current on input. Some .5 ampere or so will be the magnetization current needed to energize the xformer.  Watch for trouble, smells etc. Be damn careful what you touch when you do this. Trust nothing. Pull the plug out while you think things over.  
 Later in ref to the rectifiers, if they are mercury vapor types (like 866, 872) we need to run them with filament only for about an hour. We need to reconstitute them, distribute mercury etc. Absolutely no HV during this test.

Louis

-----Original Message-----
From: njarc-bounces at mailman.qth.net [mailto:njarc-bounces at mailman.qth.net] On Behalf Of StephenTetorka at cs.com
Sent: Thursday, November 11, 2004 12:18 PM
To: njarc at mailman.qth.net
Subject: [NJARC] Megohms in primary?


Hi all:

I'm starting my checkout of the W2PLY AM/CW rig with the 95 pound power supply.

With no power supplied, when using a VTVM from either primary lead to ground of the main power transformer, I get a reading of 15 megohms with the SPST in the primary in the OFF position. I get 5 meghoms in the ON position - which completes one primary leg circuit allowing the 115 VAC to primary.

Naturally, I'd expect infinity on this open circuit.

Not much there: terminal screws on the back chassis; hvy AWG to the switch, a lamp indicator in parallel on the primary amd the xmfr bolted to the chassis.

I would guess that some insulation somewhere has 'gone old'.

Your generous comments and suggestions most welcomed.

Regards,
Steve
WA2TAK

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