[Amps] Transformer core shorted to secondary winding??

[Karl-Arne Markström]

Have you measured the no-load DC voltage (the 811A's pulled out or biased off) 
with the HV probe?

There are not so many components that can fail in such a circuit,
and usually they tend to give out smoke in the failure process.

>From the symptom description, it may even be the case of one open rectifier branch so you only 
have half-wave rectification. This also would show up as a large 60 Hz ripple voltage as soon as
the output is loaded, which could be verified by measuring the voltage over the HV meter 
divider resistors R6 to R8 with an oscilloscope under different load conditions.

73/
Karl-Arne
SM0AOM


----- Original Message ----- 
From: "Bill Smith" <ko4nrbs at yahoo.com>
To: "S. J. Blackwell" <w5lu at hotmail.com>; <craxd at engineer.com>; <amps at contesting.com>
Sent: Sunday, July 24, 2005 1:33 PM
Subject: Re: [Amps] Transformer core shorted to secondary winding??


> 
> 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.
> 
> This is an old Heathkit HA-10 Warrior.  The orginial
> problem was that the plate volage is low, about
> 900vdc, and the power out dropped.
> 
> Resistance of the two secondary windings to the CT is
> 58 ohms and 68 ohms(leads lifted).
> 
> 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.
> 
> 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.
> 
> The schematic is here:
> http://www.geocities.com/ko4nrbs/HA10ampschematic.GIF
> 
> 73,
> Bill
> --- "S. J. Blackwell" <w5lu at hotmail.com> wrote:
> 
> > 
> > No.  As one goes out from the core the capacity to
> > the core goes down. He 
> > should ground the CT and recheck. He was measuring
> > between the floating 
> > secondary and the chassis.
> > 73,
> > Sam, W5LU
> > 
> > >From: "Will Matney" <craxd at engineer.com>
> > >To: amps at contesting.com
> > >Subject: Re: [Amps] Transformer core shorted to
> > secondary winding??
> > >Date: Sat, 23 Jul 2005 21:06:26 -0500
> > >
> > >Sam,
> > >
> > >If it were capacitance causing this, the voltage on
> > either side of the 
> > >secondary would give an equal voltage reading
> > wouldn't it?
> > >
> > >Best,
> > >
> > >Will
> > >
> > >
> > >----- Original Message -----
> > >From: "S. J. Blackwell" <w5lu at hotmail.com>
> > >To: craxd at engineer.com, amps at contesting.com
> > >Subject: Re: [Amps] Transformer core shorted to
> > secondary winding??
> > >Date: Sat, 23 Jul 2005 20:32:37 -0500
> > >
> > > >
> > > > Bill,
> > > > Before going off on this transformer, look at my
> > off list message.
> > > > You are most likely measuring capacitively
> > coupled volts with a
> > > > high impedence volt meter. Ground the CT and
> > remeasure you should
> > > > get 1700 volts  (or more with late yrs higher
> > line volts) between
> > > > each side and ground.
> > > > Sam, W5Lu
> > > >
> > > > > From: "Will Matney" <craxd at engineer.com>
> > > > > To: amps at contesting.com
> > > > > Subject: Re: [Amps] Transformer core shorted
> > to secondary winding??
> > > > > Date: Sat, 23 Jul 2005 20:14:05 -0500
> > > > >
> > > > > Bill,
> > > > >
> > > > > It definately has a high-ohm short in the
> > secondary. They've
> > > > > wound the primary on the outside which I dont
> > like to do. That
> > > > > way the secondaries leaking to the core
> > instead of the primary.
> > > > > If the primary had been the first coil and it
> > did that, it would
> > > > > blow a fuse most likely. The best check to
> > find it is use a
> > > > > megger or a hipot, and it would make it show
> > quickly.
> > > > >
> > > > > Best,
> > > > >
> > > > > Will
> > > > >
> > > > >
> > 
> > 
> > _______________________________________________
> > Amps mailing list
> > Amps at contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> > 
> 
> 
> Bill Smith KO4NR
> 
> 
> 
> ____________________________________________________
> Start your day with Yahoo! - make it your home page 
> http://www.yahoo.com/r/hs 
>  
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> 
> 
> -- 
> No virus found in this incoming message.
> Checked by AVG Anti-Virus.
> Version: 7.0.338 / Virus Database: 267.9.4/57 - Release Date: 2005-07-22
> 
> 


-- 
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.338 / Virus Database: 267.9.4/57 - Release Date: 2005-07-22