A bleeder resistor should not be so hot that it smells or discolors.
1500V over 50000 ohms generates about 35 W, so an 100 W resistor has a
reasonable
safety margin.
A way to check if the full-wave circuit is symmetrical is to plug one known
good diode
alternately in the 866A sockets and leave the other empty. The no-load voltage
should be the same either way. If the voltage becomes lower, you have a problem
with one half of the secondary winding.
It is difficult to fully test an HV power supply without suitable DC dummy
loads,
if all else fails you could connect 12 100W light bulbs in series over the
output
of the rectifier (with due respect for the HV).
If you have a Variac, try to increase the input voltage slowly from zero with a
load
over the output and watch out for jumps in the output voltage and/or crackling
or hissing sounds.
73/
Karl-Arne
SM0AOM
----- Original Message -----
From: "Bill Smith" <ko4nrbs@yahoo.com>
To: "Karl-Arne Markström" <sm0aom@telia.com>; <amps@contesting.com>
Sent: Sunday, July 24, 2005 2:25 PM
Subject: Re: [Amps] Transformer core shorted to secondary winding??
>
> I am using my spare plug in diodes(they are new).
> same result as with the orginial set of diodes.
>
> I measure the plate voltage without the tubes
> again(amp all wired back up as orginial) the voltage
> is 1300vdc with the HV probe and reads 1000vdc on the
> amp's voltmeter. It is supposed to be 1500vdc.
>
> How warm is the bleeder resistor supposed to get, this
> one is hot to the touch but not smelling or
> disclolored? It checked ok with the ohm meter.
>
> 73,
> Bill
> --- Karl-Arne Markström <sm0aom@telia.com> wrote:
>
> > 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@yahoo.com>
> > To: "S. J. Blackwell" <w5lu@hotmail.com>;
> > <craxd@engineer.com>; <amps@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@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@engineer.com>
> > > > >To: amps@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@hotmail.com>
> > > > >To: craxd@engineer.com, amps@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@engineer.com>
> > > > > > > To: amps@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@contesting.com
> > > >
> > http://lists.contesting.com/mailman/listinfo/amps
> > > >
> > >
> > >
> > > Bill Smith KO4NR
> > >
> > >
> > >
> > >
> > ____________________________________________________
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> > >
> > >
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> Bill Smith KO4NR
>
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