HV module for use with 7JP4? - Videokarma.org TV - Video

Tom Albrecht · #1 10-26-2010, 12:02 AM

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*** · #2 10-26-2010, 12:27 AM

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*** · #3 10-30-2010, 05:35 PM

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

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

Phil Nelson · #4 10-30-2010, 06:11 PM

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 · #5 10-30-2010, 06:24 PM

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 · #6 10-30-2010, 07:51 PM

Quote:

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.

bandersen · #7 10-30-2010, 10:31 PM

Maybe you could use a photocopier HV supply like this?

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

Dave A · #8 10-30-2010, 11:10 PM

You might try this from Chuck A.

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

John Folsom · #9 10-31-2010, 02:51 PM

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 [email protected] if you have a donor coil.

Phil Nelson · #10 10-31-2010, 03:57 PM

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

Phil

***Eric H*** · #11 10-31-2010, 04:37 PM

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 · #12 10-31-2010, 06:29 PM

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 · #13 10-31-2010, 10:43 PM

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.

John Folsom · #14 11-03-2010, 10:03 PM

I once had a Meck 7" TV. (well, I think it was a Meck, it has been quite a while since I owned it). Its HV was stable, but just would not go above 4KV no matter what I tried. Full recap, of course. Like the Hallicrafters, it used a 6C4. I built a little board with two 7 pin sockets wired in parallel which plugged into the 6C4 socket. When 2 6C4s ran in parallel, the HV was a robust 5KV. While this is not the same as the fading HV problem, it might be worth a try, and is simple to implement.

Tom Albrecht · #15 11-04-2010, 12:08 AM

Excellent suggestions. The Sylvania circuit is indeed very similar to that of the Hallicrafters. I'm certainly not averse to making an adaptor and using a bigger tube, if that's what it takes to use the original coil. If I can do the conversion without having to hack holes in things, etc., it's worth a try.

It'll be a few days before I can get back to the Hallicrafters, but I'll let you know how it turns out.

I think I tried several different 6C4s when I worked on this in the past, but I'll try it again to make sure that the fix isn't as simple as swapping the 6C4.

Tom