[Amps] Transformer core shorted to secondary winding??

[Bill Smith]

Unplugged diodes one at a time as suggested.  Measured
1300vdc with one unplugged and zero volts with it
plugged back in and the other one unplugged.

The bleeder resisotr is too hot to lay your finger on.

73,
Bill

--- "S. J. Blackwell" <w5lu at hotmail.com> wrote:

> 
> 
> >From: Bill Smith <ko4nrbs at yahoo.com>
> >To: "S. J. Blackwell" <w5lu at hotmail.com>, 
> >craxd at engineer.com,amps at contesting.com
> >Subject: Re: [Amps] Transformer core shorted to
> secondary winding??
> >Date: Sun, 24 Jul 2005 04:33:30 -0700 (PDT)
> >
> >
> >Grounded the CT as it was before at the swinging
> >choke.  The voltage at both ends of the secondary
> to
> >the CT is a little of 1700vac.
> 
> OK, now why the low DC volts?
> Let us assume that for some reason you have
> developed a situation where you 
> are now half wave rectifying instead of FWCT
> rectifying. This could explain 
> the 900 volts and the absence of smoke and fire.
> 
> Do the following:
> 1)UNPLUG AND WAIT. Then short the filter cap to
> ground.(Your test of the cap 
> wid the ohm meter strongly suggests it is good, so
> let us forget it for 
> now.)Restore all wiring to its normal status.
> 
> 2) Remove the filter cap short to ground.
> 
> 3)Remove the Plate lead from one of the rectifiers,
> doesen't matter which. 
> Now turn on the power having made sure the floating
> plate cap is not 
> shorting to ground. You should either get the 900V
> or basically nothing.
> 
> 4)Then reverse the plate cap situation and repeat
> the process. Let me know 
> what you get. Don't switch any of the rectifiers or
> do anything else. It is 
> possible that there is a short to ground on one
> rectifier cathode leg and 
> you are in the process of lowering your supply of
> spare rectifiers. This is 
> possible, but not likely.(Remember the absence of
> transformer grunts, blown 
> fuses and smoke and fire.)
> 
> 5) Watch out! That Cap could be charged. Let me know
> the results of above. 
> Please be careful.
> l
> >problem was that the plate volage is low, about
> >900vdc, and the power out dropped.
> 
> 
> The resistance checks are ok. One side of the
> secondary has to be longer 
> than the other to get the same number of turns.
> >Resistance of the two secondary windings to the CT
> is
> >58 ohms and 68 ohms(leads lifted).
> 
> See above re: the filter cap.
> >So far I have checked the oil filled capacitor with
> a
> >VOM, the needle swings up at first then drops back
> >down and shows no continuity to the chassis. 
> Swinging
> >choke and the plate transformer so no continuity to
> >the chassis.
> 
> 
> See above. Don't swap anything yet.
> >Tried another set of 811As with same result.  Tried
> a
> >spare set of the plug in diodes that repalced the
> 866A
> >tubes with same result.
> >
> Gud luk,
> Sam W5LU
> 
> 
> 


Bill Smith KO4NR

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