21zp4/21yp4??

[Tubejunke]

Sometime last year we discussed this but I need to know if a 21ZP4 can be replaced by a 21YP4. I found a Dumont tube up in the attic back home at the folks house that I must have stripped out back around back around 1984. I'm sure I saved it for a reason and I'm hoping the reason was spare parts for my 56 Philco that I still own. The crt has had a brightener for 20 years that I know of and I still get a viewable picture. It just takes several minutes to get that way. I need one of those plastic knob cover/Philco nameplates. I think they used them for several years worth of sets. Somebody here was going to get me some parts a while back but I never heard from them again. I can't say much it took me 6 months to mail a guy an old radio cabinet that I gave him. I did keep him posted the whole time though. Its that time of year again so if anyone out there has any info/parts/advice/on mid 50s Philcos drop me a line...

Tube

[Tubejunke]

Originally Posted by Tubejunke

Somebody here was going to get me some parts a while back but I never heard from them again. I can't say much it took me 6 months to mail a guy an old radio cabinet that I gave him.

I am glad to anounce that the guy got my cabinet safe and sound and one hell of a kind individual on this forum sent me some great stuff for my 56 Philco. I still dont have tha answer to the question though. I know somebody has a sub guide out there. I'm fairly certain that I can't use the YP4 in place of my weak ZP4. I think they focus differently or something. Please enlighten. It would be super if I could do the swap!

Tube

[ChuckA]

Tube,

You're correct the 21Y and the 21Z aren't interchangable. The 21Y uses low voltage electrostatic focus and the 21Z is magnetic.

Chuck

[bgadow]

You could put a 21Z in place of a 21Y because you could just keep the magnetic focus mechanism on the tube & leave the electrostatic focus connections off from the chassis. I think I am correct on that? But the 21Y won't work without the chassis being setup for it. I don't know what you need to add to make it work but I bet its more than a notion.

[jstout66]

sounds easier to just find the proper tube......

[bgadow]

So I'm breezing through the book "Handbook of 630-type TV Receivers", which covers these early sets plus spends some time talking about converting the chassis' for use with larger picture tubes. (among other things, you can convert a 620ts to a 27" 90degree crt) Anyhow, here is what it has to say about the issue at hand:
"Tubes with this construction (17HP4, 21YP4, 21XP4) provide sharp focus over a wide range of line voltage variation. When using the electrostatic focus type tubes on the 630-type chassis, remove the focus coil assembly from the neck of the tube and place it at the rear or bottom of the cabinet. (I think the ZP4 uses a permanent magnet? So you could just leave it out entirely and ignore this next part) Do not remove the focus coil from the circuit since it serves as part of the low-voltage bleeder network and its removal would cause a change in voltage divider values as well as a possible burnout of the focus coil and associated components. If desired a resistor equal to the resistance value and power rating (247 ohms at 4 watts) of the focus coil may be substituted in the circuit and the focus coil may then be removed. Pin 6 of the new kinescope must be connected to a voltage of from -100 volts to the value of the B+ boost; the exact value to be used is that voltage producing the best focus."

So I would say it could be done by merely finding a voltage to apply to pin 6, experimenting to find the best picture. I can't make any promises but thats how it reads, anyhow.

[Tubejunke]

Originally Posted by jstout66

sounds easier to just find the proper tube......

I think jstout still has the right idea. Gosh it would be so nice to be able to pop in that nice Dumont tube. I remember I saved it when I was a kid because it produced a goo bright picture. The set I removed it from was just like my set only it had a metal cabinet. I forget what was wrong with the set. Probably nothing. In the early 80's I would get old sets like that all the time and tinker with them or use them till something would screw up that I didnt know how to fix. Then I would bust up the cabinet and save as many parts as possible to keep my father from going insane. He always hated the old tvs. To me they were cool but to him and most anyone else at that time they were second hand junk. Tv shops back then were hauling them to the landfill by the truckload to make room for newer junk. Now theres 80s and 90s junk waiting to be hauled off. If you can find a tv shop. We have a few left in my county here in VA. I cant imagine how they stay in business but they do somehow. I wonder if some weird kid ever comes in fascinated by some 70's or 80's set gathering dust in the back of a shop and wants to fix it and enjoy its use. I can't see the same charm in the piles of plastic I see outside of one shop as I remember seeing in the 50's sets I remember finding. I used to like the roundie color sets as there were plenty of them in 1983 still around. Many folks were still using them as regular sets. That reminds me a guy at the flea market is holding a roundie he said I could have. I have told him for a couple of years that I have no room. Which I don't.

Thats what I hate the most about having a tv collection. Unless you are wealthy and have a very big garage or whatnot, you collect about 10 tvs and your crowded. Since antique stores think everything is worth a heavy price tag BUT a tv you can't really move the things for money. No longer can I fathom junking old sets unless they are a basket case. So what do you do? Maybe they will become some new trend in antiques and collectables as time moves on. Then I can move a few and get back into the whole thing. For now if I take on one I have to get rid of another. I may toss the couch and bring in the color roundie. I have a LaZboy. Who needs a couch???