[Heathkit] HW-8 and HW-7 toroids?

Fri, 8 Aug 2003 20:04:05 -0500

Yes, as a matter of fact, I erred when stating it was a heat problem.
Although it appears that heat can alter the permeability to a certain
extent, it does not appear to be significant.  You are right on when you
mention ESD.  This ground was well trod by Mike Czuhajewski, WA8MCQ, about
ten or fifteen years ago.  He "zapped" several ferrite toroids across a
large capacitor and found the permanent permeability shift to be very great,
while heating them in an oven and with a soldering iron was rather
insignificant.

For your info, here's the toroids that are used:

Band     Coil      Nominal      Core
                        inductance

80         L26    15.5 uh       FT37-63
             L27    27.5 uh       FT50A-63
40         L28         7 uh       FT37-63
             L29         7 uh       FT37-63

There seems to be a possibility of subbing -67 cores, but I don't have the
info at hand and the MARS net is coming on.

More later (?),
Tom
----- Original Message ----- 
From: <[email protected]>
To: <[email protected]>; <[email protected]>
Sent: Friday, August 08, 2003 6:19 PM
Subject: Re: [Heathkit] HW-8 and HW-7 toroids?

> I think standard inductors aren't used due to the close proximity
> of the coils to each other. I'm not convinced the shift is due to heat
> either, although I must confess I've never really checked into it.
>  I think those are T50 size cores and I think those should be good
> for 30-50 watts without much trouble. Maybe the problem is due
> to the DC collector current flowing through the windings, or maybe
> picking up an ESD pulse off the antenna? Does anyone know what
> mix the cores are? I would think that they would be a #2 (red) core
>  I've used T50 size cores in making miniature traps for a multiband
> dipole and had no problem running 100 watts to the antenna
> .
>
> Mark  WB8JKR
>
>
> On Fri, 8 Aug 2003 10:57:27 -0500 =?iso-8859-1?Q?Tom_N=D8JMY_-_AAR7FV?=
> <[email protected]> writes:
> > In answer to my own question, I got the HW-7 schematic from BAMA and
> > the
> > toroids are not the same.  For openers, I forgot that the HW-7
> > doesn't even
> > HAVE an 80 meter band.  Oh well.
> >
> > As for the idea of demagnetizing...I don't know much about toroids.
> > These
> > are ferrite cores, so would that apply here?
> >
> > The cores for 20 and 15 are powdered iron IIRC, and they don't
> > exhibit the
> > changed permeability problem.  Apparently the change in permeability
> > is heat
> > induced.  Being mainly a boatanchor man, I'm not sure why other
> > inductor/core types aren't used.  Comments?
> >
> > 73,
> > Tom
> > ----- Original Message ----- 
> > From: "Garey Barrell" <[email protected]>
> > To: "Tom NØJMY - AAR7FV" <[email protected]>;
> > <[email protected]>
> > Sent: Thursday, August 07, 2003 10:35 AM
> > Subject: Re: [Heathkit] HW-8 and HW-7 toroids?
> >
> >
> > > Tom -
> > >
> > > I have seen several references to this problem in the HW toroids.
> >  I was
> > > designing / building 50W transmitters in the 450 MHz region back
> > in the
> > mid
> > > 60's.   We ran into a similar problem whenever I managed to
> > vaporize a
> > > transistor in an untamed amplifier, and determined that the strong
> > DC
> > > current pulse was actually magnetizing the toroidal core and
> > drastically
> > > altering it's permeability.   Rather than wind another toroid, I
> > found
> > that
> > > demagnetizing it (by passing it through a "demagnetizer" [read
> > Weller
> > > soldering gun] loop) returned it to "normal".
> > >
> > > It would be interesting to try demagnetizing one or more of these
> > HW
> > toroids
> > > to see if that would "fix" it.   Or has this already been tried?
> > >
> > > By the way, I also discovered that you can actually "see" the flash
> > through
> > > the ceramic top of those transistors!  :-)
> > >
> > > 73, Garey - K4OAH
> > > Atlanta
> > >
> > > ----- Original Message ----- 
> > > From: "Tom NØJMY - AAR7FV" <[email protected]>
> > >
> > > > Question for the QRP guys.  I have an acquaintance who is in the
> > pre-wound
> > > > toroid business.  I have him contemplating offering the
> > problematical
> > > > 4-toroid HW-8 output set for 80 and 40 meters.  So far, every
> > HW-8 I've
> > > > encountered needed new ones to get back up to rated output, due
> > to
> > > > permeability changes.  Granted, I've only encountered three, hi
> > hi.
> > > >
> > > > My question is this: does the HW-7 also use the same parts?  I
> > was
> > > thinking
> > > > I was told that the HW-9 did not, but that the HW-7 did.
> > > >
> > > > Can someone clear me up on this one?
> > > >
> > > > Tnx es vy 73,
> > > > Tom
> > > >
> > >
> > > _______________________________________________
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> >
> > _______________________________________________
> > List Administrator: Duane Fischer, W8DBF
> > ** For Assistance: [email protected] **
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>
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