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TEK scope power osc transformer

The 3KV winding in a Tek scope's high frequency power supply transformer went open a week ago. 200-199 type in RM504 (~Tek504).

This tfx is a strange creature, wound (potted) on an e-core with a center post that has only half the x-sectional area of the outer legs. Operating at 30 khz (the only mention of ripple frequency in the manual), it has to be close to saturation, in spite of a generous 2mm total gap.

Phasing is not indicated on the schematic. My assumption has been that the driver tube is on when power transfer to the output capacitive filter rectifiers is taking place - and the circuit (and fully functional scope) will run at ~30KHz when a hand-wound sub with that phasing in-circuit (though not for long - couple of hours).

I'm assuming my problems with continued operation rest solely with the integrity of the 3KV winding structure; though there's plenty of layer insulation and creepage provided, the sub isn't vacuum impregnated or vacuum potted. It may be with some other HT issue. It may be that the power transfer is supposed to ocurr in a less stressful manner... ie while the tube is cut off.

Can anyone confirm the correct phasing?

...and of course..with only so much time available for this kind of stuff....has anyone got a spare 200-199 floating around?

RL

Reply to
legg
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You might want to try this group:

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Reply to
Spehro Pefhany

Possible sources for Tek scopes are here

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Your best bet might be to get a donor unit from Ebay. Of course, that's a gamble at best.

--
David
dgminala at mediacombb dot net
Reply to
Dave M

I have the thing up and running, with no voltage calibration issues, after having switched from mylar to kapton on the interlayer insulation, using the assumed phasing. Lousy stuff to work with.

The issue is really longevity.

There are 5mm margins at the sides of the 1mil (.0028mm) layer insulation. At 3KV peak stress, there's about 700V interlayer at the sides and of course the 3KV figuring in across the whole structure.

The original part used no interlayer insulation, but had 3x the number of layers - a tall winding - and was potted. Lasted 50 years, though hardly in constant use.

Will corona kill the shorter, wider coil, in air, before very long, or is this good enough for the scopes I hang around with?

RL

Reply to
legg

's a

If you think there is some corona

-make sure you don't have any sharp points (including from soldering); and

-use corona dope or liquid tape on exposed metal

It probably won't kill the coil, but might kill some semiconductors in the circuit - either in the driver electronics, z-axis/blanking, ...

HTH...

Reply to
cassiope

Are you sure about that part #? Usually it's XXX-XXXX-XXX. Might want to take a look here:

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Reply to
JW

This profusion of part number digits obviously occurred at Tektronix after 1960, when the 504's manual was published.

I've no doubt that more conventional core parts and construction were adopted for similar function at a later date. None of the materials I'm using would have been hard to get in the late 60's, save perhaps kapton (69 and later).

RL

Reply to
legg

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