Transductor tuning, an interesting article

Hehe, nice. Similar effect as the stacked toroids, or side windings on E's, or cross windings on four-leg cores (hard to find).

Note you want to make sure the pot cores are well deburred, around the center hole. That's usually a very sharp corner, no good for enameled wire!

Here's a classic Sony example:

(Not a photo, but who cares.)

They made a lot of those, back in the day. Mostly in Trinitron monitors it seems. Sony being Sony, of course they could afford to do their own custom magnetics and bobbins...

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

I have encountered this effect accidentally with an LC oscillator operating at about 2MHz which used a pot core. The output was being frequency modulated by the magnitude of stray 50Hz magnetic fields. This resulted in the demodulated signal looking like a full-wave rectified sine-wave. Holding a permanent magnet close to the pot core changed the demodulated waveform to a pure sine wave. Moving it a bit further away resulted in something in between, with one half cycle of the rectified sine wave being larger than the other one.

The solution in this case was to enclose the pot core in a mu-metal can.

John

With stacked toroids you have the problem of them being made of (not so) slightly different ferrites, which results in imperfect current cancellation, i.e. crosstalk. Binning is necessary. Side-wound Es don't have this problem, but the windings are hard to make without a dedicated bobbin, even a cardboard one. > Note you want to make sure the pot cores are well deburred, around the

Sure, a ball-shaped diamond cutter would be useful. I'm going to perform some experiments on the RM cores, too.

A nice one, haven't seen them before.

Best regards, Piotr

Are they using ua or ma as the control current? The graph says ma and the text says ua. I suspect ma, but want to be sure. Mikek

After reading the article, I find a different winding method with 200 turns of control winding on the bobbin, this makes me less sure of my previous conclusion and ready to change it to ua. Still a rather limited 2 to 1 range.

Mikek

Looking at my own experiments I'd bet on mA. The transductor I made of two 6mm toroids has 4:1 range and it happens @10mA (by design). The pot core has a longer magnetic path, so H must be higher, accordingly. Mine has 86 control turns.

It's just a matter of the control current you're willing to inject, not a ferrite limitation. I can get 10:1 range with 24mA (IIRC) using the device mentioned above and during an earlier experiment I went up to 100:1 heavily overloading the control winding. In fact, the test was performed to check the temperature rise with overcurrent, not the range.

Best regards, Piotr

We just ordered a used toroid winder for playing with such things.

Haven't done that since 1995 or so but somebody else did the winding.

boB

Any idea what Q does in this situation? Mikek

P.S. I once worked with a physicist that though you could make a strong mixer using a ferrite in this configuration. Although RF on the control winding.

I have some jumbo potcores 66/55 3C81 material. I put a bobbin inside with a lot of turns, old core don't really know but several hundred turns. Then I wound 20 turns in the fashion described in the article. The Controlled (external winding) has 36mH, yes milliHenries, I was surprised, next experiment will have less turns. Second surprise, the internal control winding with hundreds of turns has less inductance than the 20 turn external winding that is wound like a toroid!

Control winding inductance 26mH.

Control Inductance Current

0 mA 36mH 0.5mA 35mH 1mA 30 1.5mA 24 2mA 20 2.5mA 16 3mA 13.5 3.5mA 11.25 4mA 10 4.5mA 9 5mA 8 5.5mA 7.5 6mA 7 6.5mA 6.5 7mA 6 7.5mA 5.85 8mA 5.57 8.5mA 5.38

12mA 4.37

Mikek

Here are mine, much smaller, I presume:

Both are 2.1mH(0mA)-450uH(@10mA), the left one having much smaller inter-winding capacitance (~5pF vs. ~40pF).

[snip the measurements -- thanks!]

Can't measure the Q rigth now, a 2.5yo girl wants to be chased and takes no for an answer. ;-)

Best regards, Piotr

The gap makes a significant difference, the toroid windings see an ungapped core, the bobbin windings see a gapped core (possibly the core was manufactured with a gap?).

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I'm using an ungapped potcore. AsubL something like 18,400, IIRC. Mikek

I have a few questions. Mostly thinking about an RF mixer. When using a potcore with a bobbin winding and a external toroid style winding, aren't these fields at 90* to each other? As I understand, saturation is when all domains have been moved to be in alignment with the applied field and can change no more. Thus which direction the field is oriented doesn't matter, saturation occurs and the controlled winding loses it's inductance. That ask (or stated), If I take a potcore with a large gap and put a toroid with windings on it in the gap, then assemble the potcore with a wound bobbin on it, (threading the wires through as needed) can I then saturate the toroid with the Control (bobbin winding). OK, I'm sure I can, but it seems being in the gap, it wouldn't take much to make the toroid almost invisible. Just throwing out an idea for feedback. Thanks, Mikek