TOKO Inductors Needed for EM Theremin!

Hi everyone,

I'm building the EM Theremin shown in the 1996 article by Robert Moog in Electronic Musician.

I have been able to find every part except the TOKO inductors. I need two RWRS-T1015Z inductors- values of 100uH and 100 Q-min. The other inductor I need is one 154ANS-T1019Z values- 68uH and 60 Q-min.

Does anyone know where I can obtain these or of any possible substitute?

I've found inductors from Jameco that might work servlet/ProductDisplay?
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That one is 100uH and there is a 68uH in the same series. They have 40 Q-min and 50 Q-min, respectively. I'm not sure if that is a high enough Q value or not...?

Thanks in advance for any feedback,
Dan

The Jameco inductors are not adjustable.
To tune the oscillator pair you need at least one adjustable inductor in each pair.

The Coilcraft SLOT TEN-5-13 may work (it has a much lower Q). I believe that you can order those directly from Coilcraft.

(* jcl *)

The plans list that I need 2 separate types of variable inductors (two 100uH, one 68uH). Would the SLOT TEN-5-13 work for both or only one? If only one of the types, what inductor would serve as the other?

Slot TEN-5-13 is a 100uH inductor.

The EM Thermemin circuit schematic was updated
to use three variable inductors (47uH)
and three fixed inductors (2 47uH and 1 22uH)
for the oscillators. You may have an easier time
finding the inductors for the modified circuit.

The article is on the Moog site and is called
"Understanding, Customizing, and Hot-Rodding
your ETHERWAVE Theremin"

(* jcl *)

Thank you for the alternate modified article. If the Slot TEN-5-13 is the 100uH inductor, would the 68uH be the Slot TEN-5-11?

Could the A7BRS-T1040Z TOKO from digikey work?

Does anyone know what the values besides inductance are on the variable inductors from the revised circuit?

Now I'm not sure what schematic to follow (any suggestions?), but after looking for the 47uH variable inductors, it seems like high Q variable inductors are quite hard to find in general.

The slot TEN-5-11 could work for the 68uH.

The A7BRS-T1040Z TOKO looks like the replacement
part for the obsolete RWRS-T1015Z.

The Q for all of the oscillator inductors
in both circuits will be the same since the function is the same. The revised circuit splits the 100uH and 68uH in half (100uH is apx. 47uH + 47uH and 68uH is apx. 47uH + 22uH).

Splitting the inductance allows you to bulk
purchase a single variable inductor (which
is one of the highest cost parts in the circuit).

Except for the oscillator inductors I believe
that the circuits are almost identical. Build
whichever one you can the inductors for ;-)

(* jcl *)

The A7BRS-T1040Z is very close to the RWRS-T1015Z (Q min 80 instead of 100). I think the slot TEN-5-11 is a fair substitute for the 154ANS-T1019Z (30 Q min instead of 60).

Do you think it would be worth it to try and build the 1996 EM Theremin with parts that are matching except for these substituted inductors? What would the slightly lower Q min mean as far as performance goes?

I'd like to go ahead and give it a try!

Thanks,
Dan

One other caveat with the Coilcraft (other than the Q) may be the adjustment range. I do not how many turns it takes to get from min inductance to
max inductance on either the Toko or the
Coilcraft.

Since the Coilcraft adjustment
range is almost +-40% the adjustment will
be a lot less sensitive than the Toko which is +-10% (assuming they adjustment range of each is the same number of turns).

(* jcl *)

Couldn't I compensate for this with a potentiometer with more turns?

You could probably do the layout so that either
a Coilcraft Slot TEN or a TOKO can be used. They should be similar in size and may have the same pinout.

(* jcl *)