Generic aliexpress coils to replace original Millers

Posted: 3/4/2020 3:16:14 AM
otaviomad

Joined: 2/29/2020

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!

Posted: 11/1/2021 7:07:44 AM
DawidL

Joined: 11/1/2021

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.

Posted: 11/1/2021 10:29:53 AM
dewster

From: Northern NJ, USA

Joined: 2/17/2012

"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.

Posted: 12/15/2021 9:40:33 PM
acwest

Joined: 11/15/2021

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...

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