1948 (TS-4H) Motorola VT71 restored!

[jeyurkon]

In searching for this particular ballast for the past couple of years all I had ever found were posts from others also looking for them, going back quite a few years.

I'm surprised that the guy still has 8 left. I bought two, one as a spare. It was difficult to resist buying more.

John

[compucat]

Originally Posted by jeyurkon

In searching for this particular ballast for the past couple of years all I had ever found were posts from others also looking for them, going back quite a few years.

I'm surprised that the guy still has 8 left. I bought two, one as a spare. It was difficult to resist buying more.

John

My two 17A485459 ballast tubes arrived today and now my 9VT1 lives again. These glass tubes are so much better. I bought two so I would have a spare. I was tempted to buy more as well but I thought of the many others who have been looking for these. I am thinking of making a resistor replacement, mounting it in the set with an octal plug and if ballast tubes ever go extinct I can just plug in my resistor network and keep the set going. I want to refinish the cabinet, replace the torn grill cloth and add retrace line suppression to my set. It works very well of an Insignia DTV converter.

[jeyurkon]

Another good reason for making a resistor replacement is that if you have a problem with the set or need to do work on it you can test it with the replacement without worrying about blowing the easily destroyed ballast.

John

[Adam]

Ok, you all convinced me to try these. I ordered 2. Now do I understand correctly that these gas filled glass ballasts regulate current as the set comes on, so there would be no need to add a filament transformer to protect the 7JP4? - as I had been planning to do.

I have 3 ts-4j chassis: one just missing the ballast, and one missing the ballast and flyback. I figured I would try these tubes with those chassis (if I can find a flyback for that one). The third chassis was modified already for filament transformers, but whoever did it made a real mess of it with 3 separate filament transformers and a variety of series-parallel circuits. I got that one to work using that scheme eventually after I sorted it out, but it didn't work that well, and all those transformers didn't really fit under the chassis. On that one, given it's already modified, I thought I might as well go with making a ballast from resistors, and adding a filament transformer for the crt. Or maybe even try to make it into a transformer set entirely with all 6v tubes.

[jeyurkon]

Originally Posted by Adam

Ok, you all convinced me to try these. I ordered 2. Now do I understand correctly that these gas filled glass ballasts regulate current as the set comes on, so there would be no need to add a filament transformer to protect the 7JP4? - as I had been planning to do.
...

Based on tests that I did with a ballast that had only one bad filament I would have said no. That they behave just like a resistor. However, I was testing them under steady state conditions and as I raised the current the power dissipation got to a very high level before seeing any glow of the tube. I was afraid the Bakelite base was going to start burning.

Watching Bob's video of the tube as his set warm up changes my mind. The brief high current causes the filament to get hot enough to change resistance significantly and protect the 7JP4. The current when the tubes are cold must be much higher than what I tested the ballast to.

John

[Tubejunke]

[QUOTE=Adam;2907263]I have 3 ts-4j chassis: one just missing the ballast, and one missing the ballast and flyback. I figured I would try these tubes with those chassis (if I can find a flyback for that one). QUOTE]

I still have a small inventory of Thordarson and Merit NOS replacement flybacks and yokes. If you can get a part # cossreference for me I'll se if I have it.

[Adam]

Thanks, but the sams leaves all the cross-reference columns blank for the flyback. So I don't know if they even made a replacement for this one or not.

[bandersen]

I had originally refinished this cabinet with water based poly, but I've learned a lot since then. So I'm re-refinishing it using traditional materials.

The poly came off very easily with Citri-Strip.


Next, a little brown mahogany stain.


Then, grain filler.


I've used burlap in the past to remove the excess, but this time around I'm using a scraper. Really just an expired credit card. it worked out quite well.


I darkened in the pin-striping and edges with dark brown hobby paint then sprayed on some lacquer sanding sealer.


I applied a set of new gold decals to the control area.


Next up a little toner lacquer and the finish coats.

[fox_rivers]

Originally Posted by bandersen

I had originally refinished this cabinet with water based poly, but I've learned a lot since then. So I'm re-refinishing it using traditional materials.

The poly came off very easily with Citri-Strip.


Next, a little brown mahogany stain.


Then, grain filler.


I've used burlap in the past to remove the excess, but this time around I'm using a scraper. Really just an expired credit card. it worked out quite well.


I darkened in the pin-striping and edges with dark brown hobby paint then sprayed on some lacquer sanding sealer.


I applied a set of new gold decals to the control area.


Next up a little toner lacquer and the finish coats.

Looks good! What was wrong with the water based poly?

[bandersen]

Just like regular poly, it looks kinda "plasticy" compared to lacquer. Lacquer is also what they used originally. That being said, I have seen refinishing done with poly that looks pretty good and you'll find plenty of arguments pro/con poly vs. lacquer.

Personally, it took a while to get the hang of lacquer, but now I really like it.

[Reece]

I always use lacquer since it's what was used from the early thirties on (shellac before that.) I keep a few old credit cards too, just for scraping off filler. Filler makes a big difference in the look and makes finishing easier as the pores of the wood are closed and it doesn't take as many finishing coats. Good looking job!