EM Theremin - TOKO Coils

Well I am a newbie to posting, but not new to electronics, nor to this site. I have been reading all the posts and it takes a LOT of time!

For some time now, I have been interested in building an EM Theremin. The hardest part was locating the obsolete TOKO IF coils. These are the ones labled 154ANS-T1019Z (68uH) and RWRS-T1015Z (100uH). As of today, I found a company who still has some left.

http://www.jabdog.com/toko-ez.htm

The coils that you are wanting are 2 of the EZ-1015L (100uH) and 1 of the EZ-1019 (68uH) coils.

Just to scare all of you, (Especially FredM.. haha), I am a college student. I graduate with my BSEE, in December of 2009, from ITT Tech. I have been playing with electronics and designing my own circuits and boards now for over 20+ years though. (I'm 43 now) I also build guitars, amplifiers, and effect pedals, mostly tube-type. I also design and consturct printed circuit boards, of which I will have to do for the EM Theremin. (I try not to build things from kits, they just seem so.... easy)

It's nice to see that the old nostalgic electronics are not all gone!

I hope the information here helps out some others to keep the Theremins alive!

Eddie

[i]Just to scare all of you, (Especially FredM.. haha), [/i]

Welcome to TW Eddie! Its always good to have another Electronics Engineer here! ;-) I look forward to reading your postings!

Thanks FredM for the greeting! I appreciate it. I am also looking forward to some more of your looong posts! Most of which are extremely interesting and informative.

I've been meaning to ask this for quite some time.

Luckily he was able to find a website that had these components available, althought it seems others were not so fortunate.

Are there no other devices of the same era (or later) that used these components in large numbers? I would assume most of the ones that haven't already been buried in a landfill could be had relatively inexpensively.

What other devices would have used these particular components?

[edit] BTW...Welcome to Theremin World Eddie.

The TOKO 10 EZ series may today in this case be replaced by the newer and smaller 7 or 5 series. The oscillator design of the EM theremin is so stable that slight variations of the Q factor will not be important.

[i]Luckily he was able to find a website that had these components available, althought it seems others were not so fortunate.[/i]

Jeff S,
It has taken me all weekend to find some company that still had them. When parts become obsolete, you either have to do loads of searching, or redesign that part of the circuit.


[i]What other devices would have used these particular components?[/i]

Alot of RF type of devices used these types of coils. The main problem with that though is that unless the unit being stripped used the exact part, then you have to redesign the circuit again. As long as the inductance is relitively close to the 100uH and the 68uH and that they are variable, then anything could be used there. The hardest part is finding one that has a fairly high 'Q' factor.

Thierry,
Yes, one could use the TOKO coils from the 5 or 7 series pretty easily, IF (That's a BIG IF) the person putting them in the circuit knew what he/she was doing. If they want to build the circuit to the same specs as the schematic, then they would need the 10 EZ coils. Otherwise, they can be like me and like to change things and see what wild side effects they can have! ;)

And Thanks Jeff S for the welcome!

No side effects. The EM theremin oscillators are the same as in the Moog Etherwave Standard, where they use a 47uH fixed inductor in series with a 47uH variable inductor instead of the 100uH variable inductor. The oscillator design is so robust that it will even oscillate with some copper wire windings on a bumf roll.

The coil I have listed in my notes is the
Toko A7BRS-T1040Z which is 100uH Q=80 (796KHz).
IIRC it is pin compatible with the original coil.
There are 18,000 pieces in stock at Digikey.

(* jcl *)

[i]"The oscillator design is so robust that it will even oscillate with some copper wire windings on a bumf roll." - Thierry [/i]

I agree - I have messed about with all sorts of coils and configurations (coils wound with counter / bifilar turns having variable resistor to adjust effective inductance) and the Moog oscillator has proved to be extremely tolerant.

I have always found the equalizing coil to be the bigger problem - as the tuning of this is completely dependant on the antenna capacitance.. one reason I abandoned this method of linearization a long time ago.

Ok, i'm coming late to this party...

Inspired by Eddie's work building the "EM" Theremin, i've been looking into building one as well. I'm trying to decide between the "EM" circuit and the EW circuit from the "hot-rodding" manual.

They're almost the same, of course, but i'm no EE so i just wanted to make sure:

The changes in capacitor values in the oscillators - is that to compensate for the slightly different inductor values (94uH and 69uH instead of 100 and 68)?

If i got "real" 100uH and 68uH inductors, should i use the capacitor values from the EM article?

Also, would a 66uH inductor require further revision of the volume oscillator? I've found this current part: Toko BKANS-K4087HU (66uH, Q=60 @ 2.52MHz) (digikey # TK1421-ND)

Thanks,

eric.