[Boatanchors] Re: [Hallicrafters] Replacement Capacitors

Mon, 13 Oct 2003 09:32:31 -0400

1)  They equalize the voltage drop across the capacitors much better.  It's
more uniform than if you didn't use the resistors.

2)  They bleed the voltage off the caps once the power is removed.
Remember the time constant is determined by the formula:  t= 1/(RC)  where R
is in ohms and C is in farads.   So,   for 20 uF caps and 100K resistors,
t=1/(100000 x 0.000020) = 1/2 or one half second.   After voltage is
removed,  the voltage will drop to 66% of it's initial value in 0.5 seconds.
So, even after one half second, that still a good zap from a 450V capacitor.
Always short them out manually (with power removed or course... :-)  before
touching them.

73 Mark K3ZX

----- Original Message -----
From: "Greg Mijal" <[email protected]>
To: "Mark Bell" <[email protected]>
Sent: Sunday, October 12, 2003 11:36 PM
Subject: Re: [Hallicrafters] Replacement Capacitors

> Hi Mark:
>
> You might want to explain why resistors across series capacitors.  There's
> probably a dozen or so folks that are making electrolytic capacitor
braclets
> right now.  Reply to group is cool.
> 73's
> Greg
> WA7LYO
> ----- Original Message -----
> From: "Mark Bell" <[email protected]>
> To: "Bill" <[email protected]>; "Philip Atchley" <[email protected]>;
> <[email protected]>
> Sent: Sunday, October 12, 2003 7:48 PM
> Subject: Re: [Hallicrafters] Replacement Capacitors
>
>
> > and don't forget those resistors across each of 'em !!
> >
> > Keep us posted !!
> >
> > 73 Mark K3ZX
> >
> >
> > ----- Original Message -----
> > From: "Bill" <[email protected]>
> > To: "Philip Atchley" <[email protected]>;
> <[email protected]>
> > Sent: Sunday, October 12, 2003 11:29 AM
> > Subject: RE: [Hallicrafters] Replacement Capacitors
> >
> >
> > > Good point!  I agree.  For some reason it didn't occur to me to
> > > use more than 2 caps.  (3) is definitely the way to go.  Thanks
> > > for the advice.
> > >
> > > K2WH
> > >
> > > -----Original Message-----
> > > From: [email protected]
> > > [mailto:[email protected]]On Behalf Of Philip
Atchley
> > > Sent: Monday, October 13, 2003 7:10 AM
> > > To: [email protected]
> > > Subject: Re: [Hallicrafters] Replacement Capacitors
> > >
> > >
> > > Hi.
> > > I think that if the original circuit was rated at 10 uF 1200 Volts
then
> I
> > > would, AS A MINIMUM use three 33 uF 450 VDC capacitors in series for a
> > value
> > > of 11uF at 1350 VDC.  GOOD repair/overhaul practice dictates that all
> > > replacement capacitors MUST at least equal the originals in value and
> > > exceeding those values a little doesn't hurt, especially in today's
> world
> > > where the line Voltage is HIGHER than the gear was designed for!
> > >
> > > 73 from the "Beaconeers Lair".
> > > Phil, KO6BB
> > >
> > > DX begins at the noise floor!
> > > [email protected]
> > > Merced, Central California
> > > 37.18N  120.29W  CM97sh
> > >
> > > ----- Original Message -----
> > >
> > >
> > >
> > > > Going from memory here..... cuz I can't find my HT-37 manual,  that
> 750V
> > > is
> > > > steady state.   Is that measured off of a choke ?   I'm wondering
> about
> > > > voltage transients -- that may be why the caps were originally rated
> at
> > > 600V
> > > > each.   In that case 900V may not be enough.
> > > >
> > > > The equivalent circuit would be 10 uF at 1.2 KV.
> > > >
> > > > 900V Seems a bit low.   Maybe someone with the schematic in front of
> > them
> > > > can comment.
> > > >
> > > > 73 Mark K3ZX
> > >
> > > _______________________________________________
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> > > [email protected]
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> > >
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> > > [email protected]
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> > >
> >
> > _______________________________________________
> > List Administrator: Duane Fischer, W8DBF **for assistance**
> > [email protected]
> > ----
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> > ----
> > http://mailman.qth.net/mailman/listinfo/hallicrafters
>
>