Theremin inductors

[MarcoMike]

Hi guys!
I "need" to build a theremin... and I need some hints... (please consider it stompable )

I found many theremin projects online, but it seems the moog etherwave is the real deal! and the schematic happens to be available online... the problem is/are: the variable inductors! I'm not able to find any variable inductor here where I live, and also online suppliers are quite out of them.... the circuit calls for three 47uH variable inductors OR two 100uH and one 68uH (even if the part numbers written on the schematic correspond to different inductors...)

first question: any suggestion where to fin them?

second question: in the remote chance I find the right inductance coils (like in a radio or something), what about the resonant frequency? (apparently TOKO makes inductor with several resonant frequencies....)
is this an important parameter for the circuit? or is it just like using different kinds of capacitors?

thank you 

[Meanderthal]

 The 'real deal' would be the RCA, but it also has mysterious inductors as well...

[SonicVI]

Mouser probably has them. 

[Ripthorn]

Something you could do (though it would be more involved) is to build some active inductance-simulation circuits.  These typically use transconductance amplifiers, if I recall correctly, but you could use a potentiometer to control a variable inductance value.  Might even be cheaper than variable inductors.

[MarcoMike]

this sounds extremely cool... but I guess it's a bit "too advanced" for me... in case of problems the debbugging would be just random...

but i've found some inductors at work... did I ever mention I do research on waste?? and apparently we have some boxes of old tv sets circuitry samples...
Updates tomorrow!

[sean k]

I've got a populated etherwave board and those 47uH tuning inductors just look like the regular 455MHz radio inductors, though I may be wrong, they come in sets and the black ones, which are on the etherwave board, should be part of the sets you usually buy them in. White, yellow red and black maybe.

[WLS]

Who might have them could be this guy http://www.danscloseoutsandspecialdeals.com/.

He seems to carry a lot of SW stuff.

Bill

[MarcoMike]

ok... here is what I found at work: first of all: the good old days when inductors were probably as easy as resisors:



then, I found plenty of this kind of variable inductors... but I have no idea how to understand their specs.



any suggestion?

Thank you Bill for the link... some very interesting stuff there... but shipping costs and payment are killing every good deal from that guy... sorry.

[ballooneater]

You can get free samples of inductors over at Coilcraft.  I believe they have the correct values for an Etherwave Theremin. 

[MarcoMike]

FREE SAMPLES?!?! how ccomes they even pay for shipping??! where's the trick??

[zyxwyvu]

FREE SAMPLES?!?! how ccomes they even pay for shipping??! where's the trick??

They're usually intended for people who will actually buy a few thousand later on (assuming the samples are satisfactory). Some companies are ok with sending free parts to students and hobbyists, some aren't. Personally, I order plenty of samples, but it's a fairly delicate topic around here.

[MarcoMike]

inductors requested 

i'll let you know....

[doitle]

I need an inductor tester because I've got like 100 or more sitting around and have no idea what value they are... :/ Maybe I'll make up a PCB and make a tester with a uC or something that might be a fun project.