On Thu, 15 Nov 2007 19:51:14 -0500, "Uncle Peter"
wrote:


"miken" wrote in message
.. .
I've got a number of small 10.7 Mhx FM bandwidth crystal filters I
want to dismantle to recover the crystals for making a narrower
bandwidth filter.

What is the best way to open the can? I have a small butane torch
which I could use to try and melt the solder the joint around the
perimeter of the base of the can, but I don't want to harm the
crystals.

Does anyone have any experience of this, and would I perhaps be better
to hack the end off the can, and get into it that way.

Thanks de miken, zl1bnb

Miken

Some of those FM IF filters used cascaded monolythic two-pole filters
with small matching capacitors between the sections. It may not be
a lattice filter like I suspect you are anticipating.

I've opened those cans by heating the seam with a large iron, just enough
to get a small screw blade started to gentle prying the seam apart.

Regards

Peter


Thanks Peter for that advice.

I dug out the 100watt Solon iron I picked up at a flea market about
three months ago, and followed your suggestion with a little bit of
trepidation; it wasn't too difficult at all.

These filters have 4 crystals in a lattice configuration, with
interconnecting capacitors and matching inductors at each end. The
crystals are mounted on a small FR-4 pc board, which would seem to
insulate them from the heat input into the can, so I doubt they would
be heat-affected.

It seems to me that the filters with a casting resin filling in the
base, rather than with a metal base soldered into place are more
likely to be monolithic filters.

I'm sure I'll have enough to make the filter I need (for a
Pic-a-Star).

Next step is to determine the crystal characteristics.

de miken, zl1bnb