[Hallicrafters] Hallicrafters Piston Trimmer Query

[Mark Bell]

Yeah, I have to agree with Ed.  Before trying something that may bust a
trimmer or slug,  try to get a correct part.

Surplus Sales of Nebraska has the 39pF N330 2% 500V dogbones for $1.25

http://www.surplussales.com/Capacitors/RF-TempDogbone.html

73 Mark K3MSB




----- Original Message ----- 
From: "Edward B Richards" <zuu6k at juno.com>
To: <k9tr at dtnspeed.net>
Cc: <hallicrafters at mailman.qth.net>
Sent: Thursday, January 20, 2005 7:10 PM
Subject: Re: [Hallicrafters] Hallicrafters Piston Trimmer Query


> Two suggestions;
>
> 1. replace C39 with the correct part.
> 2. Replace C59 with a new one.
>
> 73, Ed Richards K6UUZ
>
>
> On Thu, 20 Jan 2005 17:56:46 -0600 "Mark Shaum" <k9tr at dtnspeed.net>
> writes:
> > My SX-111 is on the bench.  After many moons on the shelf it
> > developed
> > some instability on 20 meters that was not bandswitch related,
> > thankfully.  Component substitution determined the culprit was C39,
> > a 39
> > pf N330 dogbone ceramic in parallel with the HFO inductor.  I
> > replaced
> > it with a 33 pf NPO temp coefficient disc (which measures 35 pf) as
> > it's
> > all I had close to 39 conveniently available.  The 111 drifts a bit
> > anyway, so I'm not overly concerned about the N330 temco rating.
> >
> > As it turns out that 4 pf makes for a major frequency bump.
> > Correctable
> > by adjusting the inductor, but WWV, which shares the coil, is then
> > off
> > by an inch or more on the dial. I could easily compensate by
> > adjusting
> > trimmer capacitor C59, a 3-30 pf piston style trimmer which is also
> > in
> > parallel with the coil.  Except that the lead screw for this
> > trimmer,
> > and all other trimmers in the set, are soldered in place.  I wicked
> > away
> > all visible solder and still cannot budge the lead screw on this
> > trimmer.  Much heat applied, it still won't budge, I fear any
> > greater
> > torque will sever the lead screw.
> >
> > I know Hallicrafters solder-sealed trimmer lead screws in some other
> > sets.  Has anyone actually been able to determine if these are
> > re-adjustable at all when the solder is removed or were these some
> > form
> > of cheap set, solder, then forever forget adjustment style of
> > capacitor?
> > The Halli manual I have for the Mark I calls for adjusting these
> > trimmers as part of the calibration routine, so I suspect not all
> > were
> > soldered in place at the factory.
> >
> > Normal trimmers won't work well here as a delta change of a couple
> > pf
> > will put you off by 100 khz or so, making the usual diddle stick
> > trimmer
> > twist very touchy.  The piston style trimmer makes sense, as you
> > have
> > more fine adjustment room.
> >
> > If I can find a small piston trimmer in in the junque box to
> > install, I
> > may remove this trimmer and likely perfom some destructive
> > disassembly
> > to determine what the innards look like.  But tossing the question
> > out
> > first, I'm sure others have been in this situation.
> >
> > 73! - Mark
> > ------------------------------------------------------------
> > Mark Shaum K9TR
> > email: k9tr at dtnspeed.net
> > http://www.qsl.net/k9tr
> > ------------------------------------------------------------
> >
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