Early Sylvania Roundie on the 'Bay

[Steve McVoy]

Would it be possible to use high voltage zeners to make a replacement coretron? I see 300v 1w zeners available for about 10 cents each at Mouser. The 70 or so needed for 20kv could fit in the old can.

[old_tv_nut]

Originally Posted by Steve McVoy

Would it be possible to use high voltage zeners to make a replacement coretron? I see 300v 1w zeners available for about 10 cents each at Mouser. The 70 or so needed for 20kv could fit in the old can.

That's an interesting thought - even if the regulator had to draw 3 ma max, that would be 0.9 watts each. I assume that would require heat sinking? The hardest thing might be assembling the string in such a way as to avoid arcing over or gradual carbon tracking of whatever you mounted the diodes on.

[Steve McVoy]

3 ma can't be right. That would be 60 watts at 20 kv. Since the voltage drop across each diode would only be 300, I don't see a problem with arcing except maybe at the ends where the diodes would have to be looped around to fit. HV insulating cambric would solve that.

[JB5pro]

so I suspect it must be a 21AX. He has a radio repair shop close to Fort Lauderdale. He seemed to be the sort that would be very difficult to deal with but I have been wrong many times before. So, I suspect others wil have one but I would try to find him again if anybody would like me to do so.

[zenithfan1]

I would, I need a 21AXP22 like crazy!

[bandersen]

It's back and the BIN is up by $100.

http://cgi.ebay.com/1957-SYLVANIA-CO...-/170484029517

[old_tv_nut]

Originally Posted by Steve McVoy

3 ma can't be right. That would be 60 watts at 20 kv. Since the voltage drop across each diode would only be 300, I don't see a problem with arcing except maybe at the ends where the diodes would have to be looped around to fit. HV insulating cambric would solve that.

Rough calculation (real current will be less, since it will be limited by max red gun current):
21AXP22 spec says absolute max average current 500 microamp per gun. I was just doing the calculation to show that the zeners could withstand more than enough current to handle a black screen. (To stay in regulation, they should still be taking some current on a max white screen, when the CRT draws less than 1.5 ma. So, the flyback has to supply something slightly above the max designed CRT current, and that value has to be less than 1.5 ma. (maybe 1 ma? maybe 1.2 ma? maybe less) Then, when the CRT anode current goes between 0 and 1 ma, the regulator goes between 1.2 and 0.2 ma.

Something like that, although I don't know what the fly is capable of and what typical beam currents are in this set.

[Eric H]

It's back, wonder if the first buyer was overseas?

In big red letters:

"THIS ITEM IS FOR CONTINENTAL U.S.SALE ONLY"

Edit, I guess it said that the first time, wonder what went wrong?

[andy]

---

[jeyurkon]

Originally Posted by Eric H

It's back, wonder if the first buyer was overseas?

In big red letters:

"THIS ITEM IS FOR CONTINENTAL U.S.SALE ONLY"

Edit, I guess it said that the first time, wonder what went wrong?

I heard indirectly that the buyer was trying to back out. I guess he did.

[zenithfan1]

Wasn't me. I wonder what happened? Why click BIN when you can't afford it or whatever happened. I'm bidding again but like I said before, slim chance I'll win.
GAWD it would be cool though. That's a hole in my collection that will probably never be filled up again. Sure was cool while it lasted........

[Steve D.]

Hey Mark,

What the hell. Go for it. I know you're still smarting from having the console version and selling it. This table model sold for $595.00 in 1957. A fair piece of change back then.

-Steve D.

[zenithfan1]

WOW! Who stole it for $555? I was bidding until $500 but spaced on the end of the auction today because I was busy at work. I can't believe how cheap it went for! If I'da payed attention, it could have been mine!

[David Roper]

Not I, I'm a console guy.