Valentine's gift (or is it a shameless trick?)

[John Folsom]

Also crosses to Merit HVO-217. If I were you, Phil, I would look for a NOS replacement or a pull from some other predicta.

[Phil Nelson]

Originally Posted by John Folsom

Also crosses to Merit HVO-217. If I were you, Phil, I would look for a NOS replacement

Moyer had one in stock, so I ordered it.

Meanwhile, to satisfy my curiosity, I fixed the broken wire from the coil and gave the set a brief trial.

No sparks, and the picture had the same brightness as before. With a listening tube, however, I could hear faint ticking or sizzling noises seeming to come from the coil. Looking closely at the picture, I also saw very short, fleeting dashes (one scan line high) zipping horizontally across the screen. I suspect that the transformer does have internal shorts, as was suggested.

Earlier, the coil had taken several minutes to get hot enough to really misbehave. I didn't let it go that far tonight. While I wait for the new part, I'll power up the set just long enough to measure the HV level and the output tube's cathode current. If those are out of whack, I'd rather find out before I've installed a new flyback.

Phil Nelson

[old_coot88]

Originally Posted by Phil Nelson

...While I wait for the new part, I'll power up the set just long enough to measure the HV level and the output tube's cathode current. If those are out of whack, I'd rather find out before I've installed a new flyback.

It'll be interesting to see what the before and after readings are. Interesting too will be to see if the new fly is same as the Predicta's. That is, the replacement consisting of only the primary windings and 'tire'. You have to reuse the whole frame and core and the paper spacers between the 'C' halves since they determine resonance.

[Phil Nelson]

Originally Posted by old_coot88

Interesting too will be to see if the new fly is same as the Predicta's. That is, the replacement consisting of only the primary windings and 'tire'. You have to reuse the whole frame and core and the paper spacers between the 'C' halves since they determine resonance.

I'm still debating whether to leave the repaired flyback alone (works fine, so far) or install the new one (hey, what else did I buy it for?).

This looks like a pretty complete replacement. It's physically smaller and it has different insulation. No wax -- yay!



Phil Nelson

[old_coot88]

Originally Posted by Phil Nelson

This looks like a pretty complete replacement. It's physically smaller and it has different insulation. No wax -- yay!

Hmm. Differnt supplier, evidently. Ours was the wax version and came sans the frame.
The ones for Predictas were the only replacement flybacks I ever saw supplied that way.
oc

[leadlike]

I've heard the same thing from other sources about Predicta flybacks (you only got the windings for a replacement). I think Phil's set takes exception to what we have come to expect with the Predicta name (crappy construction) as it was a top of the line set for them at the time.

[wa2ise]

Originally Posted by Phil Nelson

however, I could hear faint ticking or sizzling noises seeming to come from the coil. Looking closely at the picture, I also saw very short, fleeting dashes (one scan line high) zipping horizontally across the screen. I suspect that the transformer does have internal shorts, as was suggested.

As you have ordered a replacement, you could risk a few experimental fixes on the old one. I've used runny epoxy to fill in small cracks of the plastic surface of more modern flybacks. And there's a product called "Corona Dope" I think intended for the purpose of painting old flybacks. That the stuff, when dry, has a higher dielectric constant than air. And not allow arcs to happen. That it wicks itself into the flyback windings to fill air gaps. Presumably the original coatings and insulation has dried out and cracked, creating air gaps. This assumes that there are in fact no shorts.

[Phil Nelson]

Yes, I removed the old wax and recoated the coil with black "sensor safe" RTV, and then fixed the broken wire from the coil to the HOT cap. No sparks, no corona. It makes a great picture. Listening with a tube, I can hear faint ticking or sizzling from the coil.

Making some quick measurements, I got -45V on pin 5 of the HOT and 165V on pin 4. Neither of those seems alarming. Disconnected the cathode lead at pin 8, but my DMM wouldn't give a current reading there, for some reason.

I've used corona dope before, and it's good stuff. I didn't have enough left in the little bottle for this whole coil, though.

Time to set this aside until the new flyback arrives, I think.

Phil Nelson

[Phil Nelson]

Hmm, maybe that fix worked after all. It's been playing continuously for hours with nary a blip. I turned off the set to feel the flyback and it's not even warm.





Vertical linearity still needs improvement, but that's about all I've got left to fret over.

Phil Nelson

[Kevin Kuehn]

Picture looks super sharp from here.

Kevin