455kHz IF transformers

[Martin Brown]

I know these things have practically gone extinct, but I would quite
like to find 3x 455kHz 2nd IF transformers (white slug) and a 3rd IF
transformer (black slug). I notice others have had difficulty finding
them too. None of the usual places has anything at all in this line.

I want to build a theremin for a science lecture so the ability to pull
the oscillators well off frequency by stray capacitance is essential.
Ceramic resonators just will not do...

I suppose I could wind the transformers by hand, but I think for this
application it would be more stable to have three identical ones machine
wound rather than DIY. Best I can think of is to go round car boot sales
buying up a few dead transistor radios. There must be a better way but I
cannot see it at present. Any other ideas?

Thanks for any suggestions of a UK or EU supplier (failing that a US
supplier who will export what will be a very small order).

Regards,
Martin Brown

 

[Rich Grise]

How does "stable" apply to a _theremin_, for heaven's sakes? ;-)

Hand-winding goes a lot faster with a jig of some kind and a drill.
And hand-winding doesn't cause unstable coils, unless you've done a
supremely crappy job of winding it.

What if you used some kind of RC oscillator with high resistor values;
if it's not sensitive enough at audio freq's, then make a couple at some
RF freq, and it plays the heterodyne?

You'd just have to design the two such that one is sensitive to the
"antenna", which could be fun.

Good Luck!
Rich

 

[Rich Grise]

Failing all of those suggestions, i could send you two Radio Shack AM
trasistor radios..

Hey - he'd have a ready-made theremin; just string the antenna to the
L.O of one and heterodyne it with the other! ;-)

Cheers!
Rich

 

[Martin Brown]

How does "stable" apply to a _theremin_, for heaven's sakes? ;-)

I don't want to make the job any harder than it has to be. I reckon
three matched 2nd IF coils for the reference local oscillator, pitch and
amplitude oscillators will have similar thermal drift with a bit of
luck. There are a lot of adjustable parameters to make it work (or not).

I found a 2nd IF in the right can at the website Leon so kindly posted.
When the article was written they were common penny items. The 3rd IF
coil still eludes me. Can someone who remembers this stuff tell me how
it differs from the 2nd IF (Q/load capacitance etc). I might be able to
use a ceramic filter in this position since it is only being used as filter.

Hand-winding goes a lot faster with a jig of some kind and a drill.
And hand-winding doesn't cause unstable coils, unless you've done a
supremely crappy job of winding it.

What if you used some kind of RC oscillator with high resistor values;
if it's not sensitive enough at audio freq's, then make a couple at some
RF freq, and it plays the heterodyne?

The LO is at 455kHz and heterodyne mixed down to audio band. I am not
sure to what extent the design depends on magnetic flux linking as well
as stray capacitance to work. Entrainment is part of the game.

You'd just have to design the two such that one is sensitive to the
"antenna", which could be fun.

I expect some amusement.

I have always wanted to build one and now I have the perfect excuse.
Then I have to learn to play the Dr Who theme on it.

Regards,
Martin Brown

 

[Martin Brown]

On 15 Aug, 17:58, Martin Brown <|||[email protected]>
wrote:

http://www.jabdog.com/

Thanks for this Leon. Looks like they still have something suitable from
the Toko range in stock. 10 off pricing while stocks last.

Cheers,
Martin Brown

 

[Circuit6040]

IF transformers available from Mouser Electronics

Check out Mouser electronics' 42IFxxx series of miniature IF and oscillator transformers. Still available 42IF300, 42IF301, 42IF302, 42IF303.

Go to mouser.com, then search "42IF3"