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What the heck is that thing?

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Voltwad

Tue Feb 17 2009, 04:16PM

Registered Member #1829 Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74

Here's an interesting xformer I found.

It looks like it might be some kind of push pull inverter or something. I pulled this out of what must have been a mid seventies era console tv. Here's how it was hooked up.

The two chokes on either side of the xformer are small toroids with about 30-40 turns. That's the best I can do for a schematic. When I say 'pulled' I actually mean kicked, as I kicked the board out of the set when I found it behind a dumpster and the board is all kinds of broken. I can't tell if the core is gapped. It whines when I connect it to my zvs driver at full power. Anyone have any thoughts? Also Here's the flyback that came out of the set.

Anyone ever seen a set of coils on the second leg of a flyback? At least the core is nice and beefy with a large winding window for winding my own.

Dr. Dark Current

Tue Feb 17 2009, 04:33PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I have seen the triple coil thing in an old TV too, I think its a magnetic amplifier (simply said, the middle control winding applies DC flux to the core so it can control the saturation voltage on the outer windings).

That's a big core, dunno what the extra winding is for, probably they wanted extra leakage inductance on it so thats why its on the other leg.

Electroholic

Tue Feb 17 2009, 06:18PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

Sometimes they dont have a seperate SMPS in for the low voltage section and just have another winding on the flyback.

Dr. Dark Current

Tue Feb 17 2009, 06:24PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Electroholic wrote ...

Sometimes they dont have a seperate SMPS in for the low voltage section and just have another winding on the flyback.

Yes but if they wanted good voltage regulation they'd have put it on the axis of all other windings.

That winding seems to have a lot of turns, maybe screen or focus?

Voltwad

Tue Feb 17 2009, 07:43PM

Registered Member #1829 Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74

There's actually an inside winding that runs the length of the leg and then the outer windings are several, some only a few turns and some almost 1/3 of the length of the leg. I'm also trying to find anything on mag amps. The thing that I have has, I'm guessing 500-1000 turns on the 'secondary' and 5-6 turns each on the 'primaries' but this doesn't seem to match the few diagrams I've been able to find of mag amps. It works well on my zvs circuit as a push pull xformer though.

Dr. Dark Current

Tue Feb 17 2009, 08:29PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

The control winding has a lot of turns to be easily controlled with DC voltage, because what limits the current is only the DC resistance of the wire. Otherwise you would need milivolts and tens of amps to do anything.

Proud Mary

Wed Feb 18 2009, 02:58AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

It's a DC biased variable permeability inductance, where the inductance is varied by the current through the control winding.

GeordieBoy

Thu Feb 19 2009, 10:56AM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

I believe these magnetic amplifiers are a cheap and cheerful way of applying something called pincushion correction to CRTs with a large deflection angle.

It's something to do with modulating the amount of horizontal deflection with a bit of the vertical deflection signal I think. If you don't do that properly, then the corners of the picture either "pull-in" from the corners of the tube, or they curve outwards into the corners of the screen, buggering up the nice geometry of whatever image you are trying to view.

I think there is at least one TV repair man on here, so he might be able to explain how that component works.

-Richie,

Wolfram

Thu Feb 19 2009, 02:03PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

There is some information on the subject here:

. See especially under "Horizontal Linearity Correction" a bit down on the page.

The waveform becomes a damped sinewave, which will be 'undamped' by restoring energy during the flyback.

One way to deal with this is to add a magnetically biased saturable inductor in series with the horizontal deflection yoke. This is called the linearity coil.

Its core is magnetically biased near the point of saturation such that the inductance decreeases with increasing current and this helps to stretch the right hand side of the scan. In other words, during the scan the coil saturates so that the inductance decreases. At the end of scan there is practically no voltage left over the linearity coil so that the deflection coil gets maximum voltage.

Anders M.

Zeus

Wed Aug 26 2009, 05:26AM

Registered Member #2316 Joined: Tue Aug 25 2009, 03:04AM
Location: Bendigo, Australia
Posts: 107

It is a pincushion tranaformer. If you check on a CRT monitor menu you shoud see
an option to change it. Also if you cut the wire between the two small windings
and drive it with a push-pull driver you shoud get 1Kv.

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