HV module for use with 7JP4?

[Tom Albrecht]

I've got a Hallicrafters 505 (same chassis as T-54) which is fully restored and works very nicely... for about 5 minutes when you turn it on. Then the HV slowly drops over the next 5 minutes until the screen goes completely dark.

In the past, I've isolated the problem to the HV RF coil, and others have reported similar problems in some (but not all) other Hallicrafters T-54 and 505 sets. Seems to be similar to problems reported for 7" Philco sets. I've baked and recoated the coil, which had a good effect for a few weeks, but it seems they reabsorb moisture or whatever the problem is, and return to their previous bad state.

Another forum member found an extra HV coil from a Motorola (which doesn't show this kind of problem), but the circuit is sufficiently different that I can't get the new coil to oscillate. The Motorola circuit uses feedback from ring around the 1B3 to drive a 25L6 oscillator; the Hallicrafters uses a feedback winding on the HV coil with a 6C4 oscillator. I tried adding a feedback coil to the Motorola coil, but things seem to be simply too different for it to work. I tried both phases of the feedback coil, and with and without the series resonant circuit used in the Hallicrafters design. But it never worked.

So I'm interested in other options:

- Anyone know of an available solid state 5 kV module? I know others have used them in various electrostatic sets with success.

- Anyone have a suggestion on how to get a Motorola coil to work in a Hallicrafters?

- Anyone have a coil which is closer to what Hallicrafters used? I'm working on a Teletone TV149 right now for someone, and its coil seems quite similar to that of the Hallicrafters. Any spares out there? Any junker Hallicrafters chassis (hopefully with a coil that doesn't have the same sickness)?

All suggestions welcome!

Tom

[Eric H]

Emco makes a HV module that can be used to replace the defective Philco HV supply but they are bloody expensive!

http://www.emcohighvoltage.com/

[Eric H]

Tom, here's the page with the information on the replacement module.

http://www.myvintagetv.com/philco_hv.htm

[Phil Nelson]

Have you ever talked to John Folsom about possibly replicating this with his super-duper coil winding machine? Knowing nothing about coils, I don't know whether it would be easy or hard . . . .

Phil Nelson

[Findm-Keepm]

Surplus Sales of Nebraska has some.

We used to cannibalize Conrac monitors for the HV supply module - and it was variable! Something like 9-17 KV with 24 volt input, and about 1.5" x 3" x 6" in size. Output was to a female plug attached to HV wire.

Cheers,

[wa2ise]

Originally Posted by Findm-Keepm

We used to cannibalize Conrac monitors for the HV supply module - and it was variable! Something like 9-17 KV with 24 volt input, and about 1.5" x 3" x 6" in size. Output was to a female plug attached to HV wire.

Back in 1979 I used to work for some toilet of a company that made boxes to convert video to hard copy on Xray film. Customers were hospitals and clinics that had CAT scanners, and they were used to using Xray film for image storage, so our box had a video monitor inside, and a lens and Xray film holder to expose. The monitors were ones intended for security camera work, or pay extra and get our box with a Conrac monitor. The QQA was multisync (long before VGA!), and used those HV modules. We swapped the CRT for a smaller but flat 5 incher. We considered using different HV modules, but the chief engineer said the excessive HV will just make for sharper spot size, and as it's inside our box, Xrays from the CRT was not an issue. Not enough to fog the film after going thru the lens it seems.

The boss there turned out to be the 2nd worst manager of my life, knocked from 1st place by some idiot boss I had at Bell Labs.

[leadlike]

wa2ise, I remember seeing such a machine in the hospital that I worked at! Basically, you stuck a big piece of sheet film into a lower drawer that contained a crt. You were essentially making a 1:1 contact print directly onto the film. You watched the action on a live monitor that sat atop the exposure unit.

The Doc saw me reading through the manual in the break room, and commented with something like "oh yeah, that thing was a real waste of money."

Not sure if the machine used x-ray film or not, but at the time I was using x-ray film in my view cameras because I could get it from the hospital for cheap, so it certainly was sensitive to light well into the visible spectrum.

[bandersen]

Maybe you could use a photocopier HV supply like this?

http://tesladownunder.com/HVsupplies...%20photocopier

[Dave A]

You might try this from Chuck A.

http://www.myvintagetv.com/philco_hv.htm

[John Folsom]

If someone out there has a Hallicrafters HV coil they would be willing to donate, I could take a look at it and see if my machine ca rewind it. I would have to unwind the coil to tet the turns counts for the windings. If the pi sections of the HV secondary are too thin, I might not be able to reproduce it. But I need a sample to play with to know.

Give me a PM or email jfrosomjr@crl.rr.com if you have a donor coil.

[Phil Nelson]

Don't have one to donate, but I believe this is the critter we're talking about.

Phil

[Eric H]

I would bet that transformer is salvageable.

I fixed one from a 10" set and it operates at about 10kv, it just up and quit on me in the middle of a recap, the ohms were fine so I figured it was just leaking between the windings.

What I did to fix it:

1. Removed it from the chassis and washed it several times in a tub of hot soapy water, I used something called Ascot Purple Cleaner but 409 or similar would probably work as well.

The reason for failure was obvious, tons of brown murky goo came out of it, probably Cigarette Tar and dust since the set was missing the HV cover and had probably run uncovered for a long time.

2. Rinsed it thoroughly several times until it stopped foaming when gently blow dried with compressed air (be very careful not to blow it apart!)

3. Dried it in the Oven at 180 for about 30 mins.

4. Let it sit overnight in a dry warm place to get all the moisture out, then sprayed it generously with some of this---> Insulating Epoxy Coating I let it run like water to get inside the windings, repeated that two or three times to get a good thick coating, let it dry and gave it a try, it worked good as new!

[jeyurkon]

That looks very similar to what's in the '49 Sylvania.

I haven't had trouble with mine yet, but the one in our family had two of those die with an open secondary. It was impossible to find where.

The secondary windings have a wire that goes from the top of one stack to the bottom of the other. In handling it or washing it one should take care not to break one of these.

John

[fsjonsey]

I have access to a bunch of older laser printers at the Helpdesk where I work. One of them might have an HV power supply of the appropriate voltage. We're just going to recycle them anyways. PM me if interested.

[Tom Albrecht]

Lots of good suggestions here -- thanks!

A little history on my coil: After I first restored my Hallicrafters 505, I noticed the HV fade problem. At that time, I found that baking the coil fixed it -- termporarily. After a week or two, it would reabsorb moisture and the problem came back.

To try to give it a more permanent fix, I washed it, baked it for a long time, and then coated with multiple coats of varnish. This kept it alive for a while, but after a month or so it was back to the same. This didn't really surprise me too much, since all polymer coatings (varnish, epoxy, etc.) are permeable to water. None of these kinds of coatings really seal out water.

After reading various related discussions here and on ARF, I've been trying to boost the drive circuit a bit and see if that can solve the problem. It already is doing pretty well right now -- I can run it for about an hour before the picture starts to bloom. However, it is very tricky to tell whether the improvement is due to my work, or just the fact that running it repeatedly over a number of days has the effect of baking the moisture out. So not clear how it will be a week or a month from now.

I also picked up a nice little muffin fan at Radio Shack which I will mount in the HV cage, since it is clear that air flow helps. With the lid on the HV cage, it fades faster than with the lid off.

What surprises me is that even after HV has faded, the coil is barely warm to the touch. It's certainly not as though the thing is really heating up.

I'll try a little more work on the circuitry, and also the fan and see where things stand. I'll also look into picking up one of the various HV modules mentioned above in case that is needed.

Tom