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

Fri, 8 Aug 2003 10:57:27 -0500

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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