Variable Inductors Stuck

[Gary Thomas-8]

Hi. Im Building the xv222 which is supplied with three
can type variable inductors (L15, 16, 17). The cores
of the inductors are frozen near the top of the form.
Manaual instructs to exercise the inductors before
placement  using the tuning shaft. Manual says they
may be tight but they are frozen. any suggestion on
how to loosen the cores without damaging them? Thanks
Gary AA1UE
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[G3VVT]

Hi Gary,
 
A tip passed on to me when I was having the same problems with some very  
small inductor cores in a commercial 2 way was to place a small amount of  
petroleum jelly on the thread topside of the core and carefully warm it with a  heat
gun or hair dryer before attempting to shift it.
 
It is very important to use the correct trimmer tool for  moving inductor
cores as some of the ferrite types are very brittle and  unforgiving. Quite a lot
of the small inductor cores also have a trimmer slot  both sides which means
the core can be reversed if one side gets broken or  can be sometimes be
accessed from the opposite side, though you cannot usually  make much headway if
the core splits. At this point the easiest option is to  order a new variable
inductor.
 
The worst situation is if the inductor core jams solid and no spares are  
available. One way out at this point is to add another ferrite/iron  dust core if
the inductance is too low or a brass core if too high. Not a  problem with
Elecraft products, but what can be a solution with obsolete  equipment when in
that situation.
 
Bob, G3VVT
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[Chris Kantarjiev K6DBG]

> A tip passed on to me when I was having the same problems with some very  
> small inductor cores in a commercial 2 way was to place a small amount of  
> petroleum jelly on the thread topside of the core and carefully warm it with
> a heat  gun or hair dryer before attempting to shift it.

I've used this trick, or silicone spray, or Kroil (a pentrating oil). As
stated, the slugs are very brittle. You may have to whittle a suitable
adjusting tip. I've had some success, a few times, extracting a core where
the adjustment hole has cracked and inverting it, so the remaining
good end is usable.

All in all, they can be a real pain. Don't force them, it just gets worse.
I think that heat alone often helps the 'stuckness'. Note that many commercial
rigs will have the slugs sealed in place with paraffin that seeps down
into the threads...

73 de chris K6DBG
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