Generic aliexpress coils to replace original Millers

So I've considered doing Christophers theremin design, however it seems waaay too expensive. Two 60$ boards is way off what I can spend on electronics atm. However, I've searched far and wide for replacements for the millers, and the most accessible are these:
https://www.aliexpress.com/item/33001219906.html?algo_pvid=0aa09153-173f-4767-8111-63a30163b3e2&algo_expid=0aa09153-173f-4767-8111-63a30163b3e2-1&btsid=0ab6f83115832915810216540ea443&ws_ab_test=searchweb0_0%2Csearchweb201602_%2Csearchweb201603_

From what I looked, these are the specs:

As you can see, it doesn't contain information for the coils we actually want (the 10mH, 4.7mH and 2.2mH) coils however we can clearly see the downward trend in min Q and SRF. Would these work? If so, how well? Thanks!

It's a great idea to replace millers with coils. I think this would definitely work but I don't how good it's gonna be. There's a need to check it on practice. And you're right, the design pricing seems to be expensive. But don't wait for it to become cheaper, especially everything related to electronics. Due to lockdowns, the shipping has become expensive as well as the products. For example, I had to wait for months to get my orders from eBay this year. Good for me, |I was able to track my orders through the tracking china post services, so it wasn't that nervous to track them. At least I knew they're not lost somewhere during the shipping.

"Would these work?" - otaviomad

If you're talking about use as coils in series with the antenna - not bloody likely.  They aren't wound in a way that maximizes SRF (minimizes self C).  When I first started out monkeying with Theremin oscillators, I tried out various coils in my electronics junk box, and most of the ones constructed this way didn't work at all.  Even the Miller / Bourns RF chokes are rather marginal.

But if they are in a circuit with a rather large C (tens of pF) in parallel with them, then they might work.  But the ferrite will give you a certain amount of temperature drift.

Where did you get the specification data? If that table is correct, the SRF seems more than high enough, and the Q doesn't look terrible. They are cheap enough that it is probably worth buying some and trying them...

Never mind, the maximum inductance there is still QUITE low

Something that might be useful for people trying to build a theremin, I have discovered a new source of cheap premade inductors. A very common stepper motor, the 28BYJ-48, is fairly easy to disassemble, and contains two 2mH air core inductors. I do not, as of yet, have complete specs for it, but it looks like it might be usable, possibly chained in series. I can get these motors for less than 5 Canadian dollars each from Amazon, so I suspect there are much cheaper sources for them. I am, if I can figure out how, going to try to figure out what their SRF is...
Ironically, I acquired the stepper motors as part of a project to build a coil winder. I'm still going to do that, but I may not actually need it anymore :-)

 

acwest, you posted the thumbnail.

Even if they are scramble wound (?) I don't think they'll work for Theremins.  Might work in a speaker crossover if the DCR is low enough.

The three EWS 10 MH coils with the antenna 10 pf is a series circuit where the antenna resonates at the EWS pitch oscillator near 286 kHz. If the antenna circuit resonates you get much better linearity, unlike a direct wire connection to a vertical rod. This is one of several unique theremin phenomenons.

If the pitch antenna circuit is resonating as you tune the pitch oscillator to match the antenna circuit frequency, using lose coupling and a scope, you tune to maximum voltage on the antenna. You want the pitch antenna tuned to slightly below the pitch oscillator frequency so you do not have frequency cross over of the pitch antenna tuned circuit while playing, this will create a flat spot in frequency in the pitch field response.

I could not find a substitute pre-made coil for the EWS approach which is series tuning, my own approach is parallel tuning which creates a pitch field response similar to the Moog E-pro. I wish I could help you with my own theremin design but I am lucky to get out of bed anymore.

My solid-state theremin design - https://www.oldtemecula.com/theremin2020/sounds/first_time7.wav

Christopher

Instead of your motor coils of unknown values, I would experiment with these. The volume side using inductors is not so important.

https://www.mouser.com/ProductDetail/Wurth-Elektronik/750311896?qs=2kOmHSv6VfQoA0Q4pVvgUw%3D%3D

Each side is 10MH with a SRF of 800khz, you might separate the two sides.

Even if they are scramble wound (?) I don't think they'll work for Theremins. acwest

I'am sure they will. You can test it with a simple oscillator (hartley or clapp type). The very advantage is the "air". So no realible warming up or other temperature-effects on inductance will occour. The Q isn't very essential for frequency stability of the oscillator.