WTB Hammond RF chokes

Posted: 12/15/2017 6:28:45 PM

Joined: 11/20/2010

So people are watching this thread.

You do it electronics is now also completely out of Hammond RF chokes, joining A1 Parts in that regard. What stinks is the supplier I found (whom I will only divulge via PM) is out of the 2.5mH value, which means I had to spend a minimum of $20 at rfparts just to place an order for one part.

shipping from Australia (Ham Radio House) to the US is over $80USD. So no way.

The 3 pi RF choke is a thing of the past.

Posted: 12/15/2017 7:32:28 PM

From: Northern NJ, USA

Joined: 2/17/2012

"The 3 pi RF choke is a thing of the past."  - BBrinkman

Indeed.  RF chokes, like virtually all commercial inductors, are the way they are mainly due to miniaturization pressures, the results of which run counter to Theremin use.  So you are stuck with hard-to-find old-school oddities that sort-of work when pressed into a service they really weren't designed for, or you wind your own.

The winding pattern would be difficult to home-brew, but there's nothing magical to the way they operate.  If your aim is to make the best Theremin coils, you start with the least temperature sensitive core (air or some formulation of ferrite) and get the self-capacitance for your target operating frequency within an acceptable range.  Correcting for temperature sensitivity is difficult to do with tempco caps and the like, it's best to nip it in the bud at the source.

Theremin EQ coils don't have to conduct any significant current, so wire gauge isn't critical.  You can pick the finest wire you can easily work with and it probably won't negatively impact Q much.

Posted: 12/17/2017 1:59:40 AM

Joined: 11/20/2010

Thank you for your input, Dewster.

once I get my Etherwave tuned up, my next objective is to try to design (yet another) analog theremin. It is interesting that with the demise of 3 pi RF chokes, future analog theremins may have to revert to using air core inductors, just like Lev’s originals.

You must be logged in to post a reply. Please log in or register for a new account.