9VT1 and ballast

[jeyurkon]

Originally Posted by compucat

I would agree with that, they are durable sets. I have a Motorola 9VT1 8" electrostatic set from 1949. It is my back and white roundie and it is well made and not difficult to work on. I need to make a ballast tube replacement for it as I was watching it and it just turned off. I knew right away what was wrong. I need to get it out of the attic and repair it. I used to have it set up and in regular use when it was working. Although Motorola sets are designed to be relatively inexpensive, they are well made and perform nicely. I would not hesitate to work on another one. Even though it was considered a "cheap" TV, many are still around and serviceable 60 years later. You cant say that about today's cheap Walmart sets.

I have a 9T1 that I recently purchased to restore. I've glad to hear that they perform well. One section of the ballast is burned out so I decided to rebuild it the hard way.

After a bit of research I'm guessing the alloy of the wire is 70% Ni and 30% Fe. It has the right temperature coefficient and seems to match the resistance of the wire in the ballast. So, I ordered some 37 qauge MWS-120. Buying it from MWS was a mistake in terms of cost. The Next time I will order it from resistancewire.com

I don't think it'll be too difficult. From reading past posts I noticed that your ballast burned out in 2007 or earlier. If my rebuilding is successful, and you're not in a hurry, I'd be happy to try to rebuild yours. If it's not a JFD brand ballast I might need to know more about it before agreeing to try it.

Why rebuild a ballast this way? Probably for the same reason I want to restore a set. That I can't explain either.

I'll be awhile before I can get the set running as you can see from the attached photo. It didn't exactly arrive in good condition.

I tried to test the 8BP4 using my B&K 465. I made an adapter for it. The tube doesn't show any shorts, but the emission is near zero. I'm not sure whether to believe the reading or not. It might need much higher bias than the 465 can supply. I realize that the tester won't find other problems like bent deflection plates. Has anyone had sucess trying to measure the emission of this CRT?

John Y.

[Hemingray]

holy lord, what happened to your set?!

[jeyurkon]

Good question. I knew there were cracks on the left side before buying it. It seems they tried to glue it with superglue.

It was pretty well packed and there was no apparent damage to the box. But you can see how it arrived. All the tubes were leaning to one side also. As far as I can tell the box was dropped flat onto one side, and also perhaps onto it's top. The g forces could have been high without damaging the box.

And with previous damage the bakelite wasn't very strong.

I didn't feel it was worth the hassle of filing a claim with FedEx.

I'm mostly worried about whether the CRT is any good. I think I can put the bakelite back together without it being too noticeable.

John

[compucat]

Originally Posted by Hemingray

holy lord, what happened to your set?!

It probably just needs a tube.

[compucat]

Originally Posted by jeyurkon

I have a 9T1 that I recently purchased to restore. I've glad to hear that they perform well. One section of the ballast is burned out so I decided to rebuild it the hard way.

After a bit of research I'm guessing the alloy of the wire is 70% Ni and 30% Fe. It has the right temperature coefficient and seems to match the resistance of the wire in the ballast. So, I ordered some 37 qauge MWS-120. Buying it from MWS was a mistake in terms of cost. The Next time I will order it from resistancewire.com

I don't think it'll be too difficult. From reading past posts I noticed that your ballast burned out in 2007 or earlier. If my rebuilding is successful, and you're not in a hurry, I'd be happy to try to rebuild yours. If it's not a JFD brand ballast I might need to know more about it before agreeing to try it.

Why rebuild a ballast this way? Probably for the same reason I want to restore a set. That I can't explain either.

I'll be awhile before I can get the set running as you can see from the attached photo. It didn't exactly arrive in good condition.

I tried to test the 8BP4 using my B&K 465. I made an adapter for it. The tube doesn't show any shorts, but the emission is near zero. I'm not sure whether to believe the reading or not. It might need much higher bias than the 465 can supply. I realize that the tester won't find other problems like bent deflection plates. Has anyone had sucess trying to measure the emission of this CRT?

John Y.

I dont know who made the ballast in my set but I can tell you that only one element is actually burned out. It is the one in the b+ line. The tube filaments still light up.

[jeyurkon]

Curious, that's the same one as in mine.

John

[jeyurkon]

Originally Posted by compucat

It probably just needs a tube.

There's a pretty funny fictional story in the 1951 Radio & Television News. The column is Mac's RADIO SERVICE SHOP by John T. Frye. It starts out with "There can't be much the matter with the set," he was telling Miss Perkins. "It was playing all right last night, but when we turned it on this morning it made a frying noise and began to smoke. I'm sure it's just a tube."

The technician and the owner then go on and on with stories about things that irk them.

John Y.

[jeyurkon]

Well, there are a couple of good reasons for the B+ portion of the ballast being dead in my set. C39 looks like it's spewed it's electrolyte. They also replaced the selenium rectifiers with 1N804 diodes. These only have a PIV of 200 volts and this doubling circuit is on the ragged edge of making them break down. I haven't checked them yet.

I'm curious about the symbol in the schematic though. It appears that they have the arrows pointing in the wrong direction. Is the symbol different for Selenium rectifiers?

John Y.

[pallophotophone]

FWIW,
The part number for the ballast unit is 17A485459 in case someone has one sitting on a shelf.

Pallophotophone