Hallo Stefan,

definitely wrong, what You say. The stray field of the centre leg winding puts the yokes to saturation. Stray field closes throug the outer legs. This means the stray field of the centre leg is the same in both outer leg-windings, but with oposite phase, thus compensating. Tha same is valid in reciproke manner for stray field of the outer legs in the centre leg. The circuit was describend in PCIM-Proceedings for controlling Switch-mode power supplies , indeed a linear variable inductor to control a self oscillating square wave oscillator.

My circuit: Class D pa in Push-Pull circuit with output transformer with three windings. Followed by the two Linear variable inductors. Followed by 7pole LP-Filter. The filter started and ended with parallel capacitors. It introduced a Inductivity as reactance between output of PA and Filter input. This is necessary as the pa ist a constant-voltage source (Ri =zero) and the LP-Filter too. For short-circuit protection and power regulation a element with constant current characteristics must be placed in between. The inductivity is not lossy, exept the dc-losses in the range of 10 W. If there is an additional impedance between PA Output and low pass filter, it will not detune the antenna, but the pa sees a higher impedance as load.

My draft of the PA failed, as any transformer winding without current flow awfully oszillates. It was not possible to shorten the peaks at the drains with snubbers. If You build a class-D PA, have a separate Load-Transformer , linked via two capacitors to the drains of the PP-Transistors, like in shortwave applications. Too often the transistors died during experiments. But an power control from 1 kW downt to 10W was possible, also with low-pass filter between Inductivity and dummy load. Now I am trying to operate an ENI 3200AMT (Electronic Navigation Industry, contains 64 * BU208, TV-deflections transistors in TO-3 case) in the lower kitchen.

If anyone is interested in the two ETD-cores , I can send them to You. What You need for experiment: Inductivity meter for hams (mine is from AADE) and Lab Power supply abt 30V/1A with variable current limitation (constant current operation) .

More upon request.

Hans-Albrecht

DK 8 ND

Gesendet: Montag, 24. April 2017 um 15:09 Uhr
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group@blacksheep.org
Betreff: Re: Fw: Aw: Re: LF: A transductor for power regulation?

Hello Hans,

Thank you for the photos. A linear variable inductor or a linear variable transformer?. Did you use it for fine tuning the resonance of your LF antenna? I can imagine this works in a small frequency range.
But if you use it for power regulation, then the load presented to the PA can have a big inductive component. Does this work well at 1 kW? For a class-E it won't. But also for other switch mode and even linear mode PAs i would assume high losses.
The DC winding is in the centre leg, ok. Makes sense. So the output winding is also on the centre leg.

73, Stefan

Am 22.04.2017 16:27, schrieb Hans-Albrecht Haffa:

Gesendet: Samstag, 22. April 2017 um 16:21 Uhr
Von: "Hans-Albrecht Haffa" <dk8nd@web.de>
An: Langwellen-Reflektor <rsgb_lf_group@blacksheep.org>
Betreff: Fw: Aw: Re: LF: A transductor for power regulation?

Gesendet: Freitag, 21. April 2017 um 22:33 Uhr
Von: "Hans-Albrecht Haffa" <dk8nd@web.de>
An: rsgb_lf_group@blacksheep.org
Betreff: Aw: Re: LF: A transductor for power regulation?

Dear Lowfers,

years ago I have constructed a power reg. with a linear variable inductor. It was possible to regulate power from 1 kW down to 10 W / 60 Ohm at 136 kHz. The temp. coefficient of the inductor is that of the material N27, power dissipation is mainly due to dc losses in the dc-Winding in the centre leg. Clampes for the core halves I cold not use, as stray field in the saturated yokes caused edding currents in the clampes. So the core halves had been fixed with bath-room silicon from the diy-store/home store. Core size is ETD59.

More detrails upon request.

55,

Hans-Albrecht DK 8 ND

cba, qrz ok

Gesendet: Donnerstag, 20. April 2017 um 21:02 Uhr
Von: "Claudio Pozzi" <smtp01@email.it>
An: rsgb_lf_group@blacksheep.org
Betreff: Re: LF: A transductor for power regulation?

On Thursday 20 April 2017 11:14:22 you wrote:

> Thanks for all the interesting contributions. The old book is a very

> nice one :-)

>

> I expect using saturated coils rather than a saturated transformer can

> give better results when it is used for keying a carrier (CW, DFCW,

> QRSS, OPERA...). But that will be rather a narrow band solution. The

> transformer has its advantages too. I will continue to improve the ratio

> between keyed and unkeyed power later...

>

> 73, Stefan

>

Some idea for the transformer...

May be that a small toroidal transformer core for mainline power supply can be useful for 2 and 6 kHz bands. But toroid are without transformer air gap.

A core from an old output transformer vacuum tube amplifier can surely be used from few hundreds Hz to 10 kHz, may be up to 20 kHz if salvaged from an Hi-Fi push-pull amplifier. Audio transformer are with air gap.

73 de Claudio ik2pii

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