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Old September 14th 05, 02:34 AM
 
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On 13 Sep 2005 17:08:48 -0700, "Tim Shoppa"
wrote:

Are the big old-fashioned IF transformers-in-a-can available
anywhere anymore? I want to make a receiver, probably double
conversion,
which would mean that I'd want several each of the 50kHz and some
higher frequency (455kHz likely).

Are these things that can be made from scratch without a lot of
difficutly? I can wind coils etc. but don't
have any transformer slug-tuned cores.

Tim KA0BTD


Hi Tim,

They are homebrewable. I needed a few 455khz for a tube RX I was
building and basically resused some old "IF like" cans by replacing
the guts with handwound coils and caps. The forms for the coils were
Horz width coils from a few dead monitors, used the slugs too. Used
one of the basic programs for solonoid coils to get a rough number of
turns and then then wound 30% less in scramble form. That gave a
basic coil and then resonated it with a cap to 500khz. Once the slug
was added it easily tuned down to 400 so I cut the slug shorter (1/2)
and it was fine for 455. The distance between the two coils (for
double tuned IFs) determines the coupling factor, or more directly
the selectivity and losses. Once you have the recipie for one winding
you can easily reproduce it.

Theres nothing special about IF cans save for they have to tune the
desired range, have a decent Q and are shielded. The outer can
however is important or that IF amp will become an IF osc. But even
the can can be liberated from salvage or made from copper, tin or
aluminum stock. I made some really nice looking cans using 1"
Copper pipe and pipe caps, heavy but well shielded. Soda straw
was the coil form and holes in the ends supported it and allowed
access to tuning slugs. Leads came out using insulated Teflon
feedthroughs. Looked very industrial.

Allison
KB1GMX