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Old 06-29-2012, 11:38 PM
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Opcom Opcom is offline
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The yokes I need are just regular tube type yokes, but I will take ss ones that have the proper diameter and degree geometry. The tube data is below.

It is possible to place a set of four V windings or H windings staggered and interleaved around the tube if the core is abandoned, but the magnetic field gradients are malformed and beam position is no longer linear to yoke current. Not that it ever is, but new errors are introduced.

The ferrite can be abandoned and there are air core yokes, but in the volume 22 it discussed that, why it is not a great idea.

I have to rewind a bad yoke here. Bought from ebay NOS in the box.. as is of course and with evidence of having been tried.. I learned from a yoke from a government XYTron display that one secret is to use few turns of heavier wire. That yoke has about 14 turns in each winding, so 28 V and 28 H. I can't examine more closely because it is two ferrite shells with windings inside and glued together. However, from the MIT volume 22 referenced above, I see how a pegboard can be made to allow the making of distributed windings that can be formed into the proper shape. If I can take the windings from the bad yoke as a template, I should be able to devise a suitable sized winding jig.

Many yokes have inductances in mH. Even the horizontal windings from solid state sets have more inductance than needed. If checked in a ss TV set, the voltage across them is 1KV peak, so it is suitable for higher inductances. Tube yokes - I never messured the voltage across the H yoke on a color set - probably pretty high. A vertical winding has lots of inductance, even on low voltage sets. It's the pulse applied to the yoke that is the true measure of the actual deflection voltage required, and we see 50-100V pulses on a ss vertical yoke for 60Hz sweep.

With a practical low voltage amplifier, the windings should be more like 50-100uH. One way to describe a yoke winding is in volts per amperes per microsecond. e.g. 100V for every ampere of current increase per microsecond. Another thing is the current, but the ampere-turns is the key to the magnetic field just like a choke or transformer. So if the yoke with 200 turns needs 3A to position the spot at the edge of the screen, then theoretically the yoke with 50 turns needs 12A. The fast yokes from that XYTron display can take that kind of current, or maybe 15A anyway. The project has to move the yoke current from -3A to +3A in 16us. well that is the goal anyway.

One cheat is putting the windings in parallel to allow more current basically cutting the voltage requirement in half. I have not experimented to see if the compensation network, the RC dongle across half the yoke in TV service, can be eliminated by this.

This said I do not intend to destroy good yokes, I need them for display of NTSC video on most of those tubes. Crappy condition yokes might get a rewind, but it is not necessary to ruin the old windings to remove them, and replace with low turns count windings for these experiments.

The yokes I am after are 50-60, or 70 degree types and fit a neck of 1 7/8" (1.875"). I can use 70 degree yokes if necessary but prefer the 50-55 degree types as well as focus coils and/or magnets for same tubes. Some older ones had a focus coil or magnet in the set as well.
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