Hi,

I was wondering if anybody could tell me where I could get a 47 uH variable inductor. I am building a theremin that has been hotrodded due to the availability of the inductors which where 3 section inductors. The circuit has been edited but it seems that they have replaced it with something that is still difficult to get hold of (I think). I found some on mouser but the cost £25 pounds each. I cannot find this value anywhere.

Thanks

Ross

 

Hello,

Have you tried ebay?
https://www.ebay.com/sch/i.html?_fr...=7288&_odkw=toko+coil+variable&LH_TitleDesc=0

Bertus

 

Hi Bertus

I looked on ebay but couldn't find them. They're perfect though

Thanks

 

Hello,

When you know the name of the manufacturers that make inductors, the search will be more easy.
Well known inductor manufacturers are Neosid, Murata and Toko.

Bertus

 

I wouldn't have thought the value or construction of an inductor for a theremin would be critical. If you can't find the exact one at a reasonable price perhaps you could brew your own.

 

Hello,

As @Alec_t said, the values may not be that important, as long as they are in close range.
There are 4 oscillators in a theremin ( as far as I know ).
Two will determine the frequency and the others the volume.
Have a look at thereminworld or thereminvox for more info and schematics:
http://www.thereminworld.com/schematics
https://www.thereminvox.com/index.html

Bertus

 

Hi again,

I now have a variable inductor of the correct value but have purchased it from a company on eBay. I have tried to look for a datasheet and asked the seller for info but they don’t have any. Does anybody know which pins are which on this component? I can see three legs that have separate wires connected to them so I’m guessing these are the legs that are used (not sure what the opposite 2 are). I would use the outer two for connecting it into a circuit, right?

Kind regards

Ross

 

Hello,

You could measure the coil with an ohmmeter.
I see four connections. Three on one side and one on the other side:



Bertus

 

Hello,

You could measure the coil with an ohmmeter.
I see four connections. Three on one side and one on the other side:

View attachment 169247

Bertus

So I’ve looked at each pin with an ohm meter and I’ve found that on the side with 3 pins the bottom one and the middle one have 2 Ohms between them and the top one of the 3 pins and the one opposite are the same. I’m guessing it would be useful to increase/decrease the value of the inductor but Ive just realised don’t have a trimmer.. I will probably have to buy one and try it again.

Ross

 

Hello,

To adjust the coil there should be a core that can be moved.
The core likely has a slit or hex opening to adjust it.
At the moment it looks like there is some wax on the core to fixate it.

Bertus

 

Hello,

To adjust the coil there should be a core that can be moved.
The core likely has a slit or hex opening to adjust it.
At the moment it looks like there is some wax on the core to fixate it.

Bertus

So, I’m not sure how to get the wax out. I tried picking it out with a pin and that didn’t work then I tried heating it up and using the pin but I couldn’t get it to budge. It’s kinda just starting to come apart in bits. Not sure

Ross

 

An inductor would have two connections. Are you sure that this isn't an RF transformer?
What is the appearance of the top body of the component? It looks like an IF transformer to me.

What kind of slug is it? Does it have a flat screwdriver slot or a hex hole?
If the slug is adjustable and removable I would try to turn it with a proper tool while heating it with a hot air gun.

 

An inductor would have two connections. Are you sure that this isn't an RF transformer?
What is the appearance of the top body of the component? It looks like an IF transformer to me.

What kind of slug is it? Does it have a flat screwdriver slot or a hex hole?
If the slug is adjustable and removable I would try to turn it with a proper tool while heating it with a hot air gun.

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/123060141717

Hey,

The product I bought was the one in the image below. The top of the body has a flat slot hole. The mechanism turns when a tool is inserted but the resistance across the pins that seem to be connected doesn’t change (if that’s what’s suppose to happen).

Ross

 

Its primarily an inductor, the resistance will not change but the inductive reactance will.
Max.

 

The resistance will not change, just the inductance.
Be careful when turning the slug as they are quite brittle.
Ah. You just beat me Max

 

I luckily found this on ebay which shows the connections within the component



https://www.ebay.com/itm/Variable-I...-Litz-Wire-Ham-Radio-Hobby-Toko-/123060141717

Thanks