Hallicrafters rebuild update.

[Eric H]

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.

[Phil Nelson]

7-inch Hallicrafters?

Phil Nelson

[Eric H]

Originally Posted by Phil Nelson

7-inch Hallicrafters?

Phil Nelson

Yes, the 506 with a T-54 chassis.

[hi_volt]

Where's the core?

[jr_tech]

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

[John Folsom]

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....

[old_coot88]

Nice job, Eric. Not trying' to be fuddyduddy, 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.

[DavidGoncalv]

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.

[Eric H]

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.

[John Folsom]

What product are you coating it with?

[Eric H]

Originally Posted by John Folsom

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.

[earlyfilm]

Originally Posted by Eric H

Piping hot from the Oven.

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

[Eric H]

Originally Posted by earlyfilm

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?


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.

[Phil Nelson]

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

[Eric H]

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.