1-125 Sylvania

[jeyurkon]

Originally Posted by jr_tech

So Scotty will have a new cathode installed in the old gun?... or does he have a supply of the triode guns?

jr

He will have the gun rebuilt. Hopefully there's nothing else wrong with the gun like an enlarged hole at the end of the gun. I don't know what all they can rebuild.

The gun in the 12VP4 uses ceramic supports instead of glass. I wonder if this makes any difference in the difficulty of rebuilding it.

John

[jeyurkon]

Originally Posted by Phil Nelson

I have wondered that, too. From what I recall offhand, I have TVs with both steel and aluminum HV covers. Those with aluminum covers are 7-inch sets with RF type supply, Motorola VT-73 and National TV-7. Those with steel covers have flyback type supplies and higher HV. Of course, maybe the cheap little TVs used aluminum simply because they're cheap little TVs. Or, possibly I'm remembering wrong and there is no real pattern.

Similar question with ventilated vs. non-ventilated covers. Perhaps they should all be ventilated, but some are not because non-perforated sheet metal was cheaper. Judging by the melted wax I've seen dripping out of flybacks, some of those covers definitely could have used better ventilation.

No answers, in short, just more questions If you had steel & aluminum containers about the right size, you could do an experiment by holding each type of can over the supply and seeing whether the RFI is different.

Phil Nelson

Since the flybacks have a core I would guess any influence an iron cover would have would be minimal.

You tempted me to look up the price of 1950 aluminum and steel because I once remember reading that before 1855 aluminum was more valuable than gold and that Napoleon III reserved the use of aluminum dinnerware for his most important guests.

Aluminum was $350/ton and steel was $47.20/ton in 1950. I think they would have gone with steel based on cost. I'm not sure how fabrication costs would differ.

My 1-108 chassis has the aluminum can. I can do the steel vs aluminum test with it. The can in my 1-108 does have ventilation hole along the top and bottom with a note on the can that they must be aligned vertically. There's a 6Y6 and 1B3 in the can and it gets quite warm. I'm tempted to stick a thermocouple in, but I might zap myself that way.

John

[John Folsom]

John, I never has one of those Sylvania sets with the 12VP4. But I admire any 10 or 12 inch cRT set with a RF high voltage supply.

[jeyurkon]

I forgot that aluminum is about 1/3 the density of steel. So it's only 3 times as expensive in 1950, not over 7 times.

John

[jeyurkon]

Originally Posted by John Folsom

John, I never has one of those Sylvania sets with the 12VP4. But I admire any 10 or 12 inch cRT set with a RF high voltage supply.

I might be reading too much into your comment, but I don't think a 10" or 12" CRT makes much of a demand on a properly designed RF high voltage supply. Spellman made an after market RF HV supply for projection sets in the 50's.

I had some trouble with mine at first, but after selecting a good 6Y6 I get plenty of HV and it's quite stable. It also seems to have gotten better the more I use the set. Perhaps the transformer had absorbed some water.

John

[bandersen]

Admiral, Motorola and Hallicrafters all used aluminum shields for their RF HV supplies. I'm not sure, but I bet it has to do the effect of ferrous alloys on the coil.

[jeyurkon]

Originally Posted by bandersen

Admiral, Motorola and Hallicrafters all used aluminum shields for their RF HV supplies. I'm not sure, but I bet it has to do the effect of ferrous alloys on the coil.

I hope to find out after going grocery shopping today. I've been taking a few days of vacation.

Phil mentioned ventilation holes. I forgot to mention that besides the holes the can on my Sylvania is painted flat black on the inside and outside. I think this was to radiate heat better.

JOhn

[jeyurkon]

Well, there were lots of #5 cans at the grocery, but they were made of paper. I thought this might be a bad idea. I found only one metal can the right size. It was decaffeinated off brand coffee. I don't see the point without caffeine.

I tried it on the Sylvania that I have working that has its aluminum can. The coffee can is a bit longer, but I didn't trim it down because with the OEM can there are 6Y6's that are too long to fit and the cap of the 1B3 is very close.

I swapped the cans back and forth to make sure there wasn't any warm-up effect biasing the measurements.

With the OEM can I measured 9.75KV. With the steel can I measured 8.98KV. I should have tried adjusting the trimmer capacitor, but I spent so much time getting it where I wanted it I didn't want to disturb it. The steel can might be causing losses, or it might only have shifted the frequency.

When I restore the 1-125 I might use it because after painting it black, it'll look pretty original. If it causes problems I'll make one out of aluminum, but it won't be as pretty.

John