Hallicrafters rebuild update.
 

Piping hot from the Oven.

First prepare your transformer by washing it with a diluted solution of Purple Cleaner (or 409), follow with a rinse of hot tap water then it's in to the Oven at 195 degrees for 20 minutes and it comes out nice and pretty.

After sitting for 24 hours or longer a light dusting with Epoxy Dielectric spray will add that extra special touch that will keep your transformer humming along for years to come.

7-inch Hallicrafters?

Phil Nelson

Yes, the 506 with a T-54 chassis.

Where's the core?

Would this treatment help the "drift"/low HV problem, sometimes observed on the early Philco 7 inch set ?
jr

The Philco 7" HV coil is a layer wound transformer, and baking in the oven does not seem to help much. But you could give it a try....

Nice job, Eric. Not trying' to be fuddyduddy:o, but it's not a flyback since it's not energized by the "fly-back" spike of a sawtooth waveform.
Just feeling' ornery this morning. :D

I read all those reports of 7" RF HV supplies going 'weak'; I decided with my Hallicrafters project to fit in an EMCO HV module to ensure solid HV.

The Philco is the only 7" that I've experienced the HV fade problem with, the transformer is completely different though.

I did have an open core RF type HV transformer conk out on a 10" Raytheon, in that case this washing, baking, coating process brought it back to life.

What product are you coating it with?

I'll be using some clear Aervoe insulating Epoxy, 3900 volts per Mil which is probably equal to or better than the original Varnish on the windings.
I am fortunate that I can buy it locally, though it costs an arm and a leg, it goes a long ways however.

The stuff is thin enough to flow deep inside the coils if desired, I put so much on the Raytheon transformer it's practically a solid mass now, but it works great.

I assume that the purpose of heating and resealing is to dive the moisture out the coil and then keep it out. Correct?

OK, first question is what is the purpose of the cleaning? To rough up the surface for the new coating to stick? To remove the old varnish?

I looked up the MDS sheets on these two suggested cleaners.

The two that you mentioned don't seem to be made for the same purpose.

The first cleaner you mentioned has some nasty chemicals in it:
SODIUM HYDROXIDE; caustic soda; soda lye
ETHYLENE GLYCOL MONOBUTYL ETHER; 2-butoxyethanol; butyl cellosolve
SODIUM XYLENE SULFONATE
SODIUM DODECYLBENZENE SULFONATE; linear alkyl aryl sodium sulfonate; Sodium
DDBSA
DIETHYLENE GLYCOL MONOBUTYL ETHER; 2-(2-butoxyethoxy)-ethanol; butyl carbitol
ALCOHOLS, C9-11, ETHOXYLATED; linear primary alcohol ethoxylate

While the other cleaner is a relatively harmless glass cleaner and it has much less of some of the same strong chemicals, it is classified as a carcinogen, while the former one is not.

I suspect that I'll be needing this procedure, as I have three 7 inch sets in line for restoration, including a T54, along with a Pilot TV37, that had high voltage issues when it warmed up, before it took a swim last year during my basement flood.

James

Yes, after washing it I needed to get it hot enough to dry it out, the cleaner is very caustic full strength but I diluted it down to a fairly weak solution.

The purpose of washing it was just to get it clean, the top had been off the cage and the coils were pretty packed with dirt, also the Phenolic board was filthy, there's really no other way to get it this clean, picking at it with Q-Tips might make it look better but it's probably no less risky than just soaking it, also I just think it's a good idea to re insulate the windings after 64 years, they usually look pretty dry on these things and if you've ever brought a screwdriver near the coils while it's operating you will see that they leak all over the place, probably still will even after spraying but I'm more worried about leaking inside the coils.

I don't know if this transformer worked prior to cleaning or if it will after, the set is being recapped and then I'll find out, it looks to be in good shape though.

I have washed them out before with no ill effects, same with Flybacks and even entire chassis, as long as they dry sufficiently they are OK, I figure being full of dirt has to be bad for them.

I have a couple of Hallicrafters waiting for restoration, too.

It would be interesting to have some before-and-after data on this treatment -- HV output before and after, or whatever else is relevant.

I have always wondered whether the moisture problem is a symptom of disuse. If you played the TV for a few hours a day for a couple of weeks, would the heat of normal operation make a difference?

Phil Nelson

On the Raytheon I didn't measure the HV prior to the transformer failing, however after I cleaned and recoated it it was obvious to the naked eye that the set had more HV, it was brighter and had less blooming.
Of course in that case it had been running on the edge of failure to start with so the "After" was probably running closer to spec.

I have a Philco that someone has transplanted what looks like a Hallicrafters HV assembly in to it, I could never get it to run reliably though, I might take another crack at it someday.

For the folks that have HV output issues, I wonder if they could monitor the RF frequency over time and see if it shifts.

The NaOH isn't necessarily harmful. True, it's a strong base and will chew up your skin/eyes, but in practice one wears eye protection, gloves, long sleeves, and doesn't use it as a dessert topping. Just don't use it to degrease yourself.

Butyl cellosolve is ethylene glycol monobutyl ether (EGBE).

Glycol ethers should give you the willies, however. Not only are they a known carcinogen associated with all sorts of tumors, but they cause testicular atrophy. (Yikes!) And the amount required isn't huge. I believe the EU and Canada tightly regulate their use and may have banned a number of them.

Phil, if your coil was known to be bad beforehand, and now appears to be permanently fixed, that would be good news indeed.

I have to admit I would be somewhat surprised if this approach offers more than a temporary fix. If moisture is in fact the problem, there is no polymer coating of any kind that can keep it out for more than a few days or weeks. Polymeric coatings are generally quite permeable to water.

Ability to insulate is mainly a separate issue, so there is no particular reason why a product geared toward good insulation would be good at keeping water out of a coil and preventing the overall lossiness in the structure that results from that. I suspect this insulating coating is a nice choice for reducing tendency for corona, etc.

I've done the clean, bake, and coat approach on a Hallicrafters 505 coil, and found the improvement was only temporary.

However, what did work was to mount a cooling fan inside the HV cage on that same Halllicrafters. Now it works fine.

Previously, the HV would start out OK and then go low after 10-15 minutes. It seemed the combination of old, moist coil and a little heat build up resulted in the fade.

And as I recently reported on ARF, I successfully replaced a Philco coil with a surplus Motorola coil, and am having good success with that.

So far have not had to resort to an alternate HV module.

I've got this set working now!
 

It looks pretty good, I changed a few out of tolerance resistors, there weren't all that many actually. Still have to get a couple 100k 1 watt but everything else is done.

It had a bad section (short) in that multi section resistor that's riveted to the chassis so I replaced them with some individual ceramic resistors.
The originals were only rated at 2 and 4 watts, the new ones are 5 and 10 watts so they aren't running hot at all, I need to find a way to neatly install them though.

I had miswired a circuit in the HV cage, put a wire where it shouldn't have been and caused a short that dragged the B+ down and was smoking the 680 ohm resistor on the 25Z6, as soon as I cleared that up it started working.

The Vertical is short, swapping out tubes makes no difference, the two 100k resistors I need are in the Vertical circuit, one is reading 179k and the other is 130k, they are supposed to be 10% tolerance so they are badly out of whack.

One other problem is the socket for the 6C4 in the tuner, it's the one on the right front corner, it loses it's heater connection some times, I'll have to replace it or see if it's repairable, I hate replacing sockets, all those wires and drilling out the rivets, ugh.

The CRT I'm using here is shot, I use it for testing just in case something bad happens I won't break a good tube.
In normal light it's unwatchable but the Camera is much more sensitive so it works well for taking pictures

The Vertical height problem was a drifted 680k resistor supplying B+ to the Vertical Oscillator, it had drifted somewhere around 2 meg, now the vertical has plenty of height.

This set has really strong audio!

Posted a short video of it running here: http://vintagetvsets.com/videos/hallicrafters2.wmv I suggest right clicking and viewing full screen.

The CRT is a NOS Rebuilt that I got off eBay, it had a short under the base cap, after removing the cap and straightening out the bent over wire it works great. Removing and replacing the base on a 7JP4 isn't a job I'd wish on anyone, nerve wracking to say the least.

The HV transformer is working great, it's been run a couple hours with no fade.

Can you take an under-chassis photo for me? Just details on the component layout.

Sure can, I ditched all the multi section paper electrolytics though and wired them individually, I was jut not in the mood to restuff the tubes and hunt down new wire for them, it came out quite neat I think.

Pictures when I get home tonight.

One problem I'm still having is some slight streaking in the picture, it gets worse after being on for an hour.

Not sure if it's HV arcing somewhere or some component in the video chain acting up. I can't hear any arcing, it's quite quiet actually and I have all the covers on the HV cage (top and bottom). Possibly a Silver Mica going bad, if this set has any of those, I'm not sure it does.

David, here's the picture, it's too big to post here so I put it on my site.

http://vintagetvsets.com/temp/hallicaps.jpg

The two big caps on the left are way overkill, they were 40@300v but I had some 47@500v so that's what I used, I added the terminal strip and wire to make it neat.