neat magnavox

[jr_tech]

Originally Posted by rob Cashin

the crt isnt that round, a little rounder than my 61' RCA but not by much...

About 1959-1961 there was a transition from the popular 17 and 21 inch rectangular CRTs to 19 and 23 inch CRTs, with the major difference being slightly more square corners. Most of this newer generation of CRTs also incorporated built in implosion protection and no longer required a separate safety glass. This generation, in general had higher deflection angles and smaller neck sizes than the rectangular CRTs of the 50s. While a few round tube sets were produced in the early 50s (i have a 16 inch 1951 Philco with a round CRT, and of course there was that 30 inch round DuMont!), most 50s B/W TVs were rectangular.

jr

[Tubejunke]

Originally Posted by rob Cashin

This morning when i powered it on, i got sound but no picture until i shut it off and lightly tapped the cap on the neck, where it was spliced. I saw in another post on here that another mag owner had the same issue (thanks for the tip). over all so far, its been a good 30 bucks

I just addressed this common issue in another thread, but I'm not sure if it's the one you saw. Actually, it applies to most all 40-60 C.R.T.s with the plastic plug and socket. What happens is the glue (epoxy?) that holds the plug steady on the end of the tube hardens to the point of being brittle from age and the heating and cooling process of the set's use. Once the bond is broken, the weight of the wiring, perhaps a brightener, and aspects of servicing like simply taking the back cover off and replacing it cause the often marginally soldered conductors (that protrude from inside the glass electron gun and into the hollow pin array) to become intermittently open connections. So, you tap on, or otherwise move the plug and socket and have a temporary fix.

For the record, you don't need to turn the set off to do what you are doing. You are just creating more guesswork and by doing that you will likely be powering the set off and on a lot more which is way more of a strain on all components than one might realize. If nothing else, you can run it with the back off and take a roll of electrical tape and with the aid of a helper have someone press on the loose plug and visually ensure that the heater is glowing inside the electron gun (it's not when it stops working). When you establish this, then you can firmly secure the plastic plug to the glass of the gun with the electrical tape.

The correct fix is to heat the pins of the plug until solder flows into them and fills them. Then you can get some of the epoxy resin that they make these days that has a sort of syringe tip and get as much as you can inside the void between the glass and the plastic plug with the pins protruding. Frankly, electrical integrity is the key here as far as the tube working properly. The importance of steadying the plastic is so that you don't eventually have the small wires inside break which would be a whole new thread.

I hope this helps...

[Tubejunke]

Originally Posted by Eric H

Some of the early 50's tubes were actually more rectangular than what came later in the decade, the early 60's is when they really got squared off for the most part.

What you have seen that appears to be more rectangular tubes in the "early 50s" and actually in the 40s were in fact round tubes like the very popular at the time 10BP4. Sometimes the manufacturers opted for a rectangular mask around the round tube. A good example of this would be looking at a picture of an RCA 8T-243. The strange thing is that they were doing this I believe before they were doing the "double D" mask which is round with the top and bottom blocked off. Perhaps all of this relates to JeffH's concept of what looks more realistic as far as viewing. The odd thing is that they did the rectangular designs first. Not to mention that many 40s sets were projection sets and the viewing area was very similar to a modern flat panel design.

Now in the early 50s the first true rectangular tubes became standard. Although they have the now classic looking rounded corners, they are in fact deemed rectangular in the engineering guide books put out by companies like Sylvania. That design stuck around until somewhere in the early 60s when the more rectangular shape that most of us would consider standard up until the end came into play.

What I don't get is why color tubes sort of went through the same development process only a number of years later. They began completely round and transitioned in the mid to later 60s to what we consider standard. Why were they round when truly rectangular black and white designs were already in place? Somewhere there is an interesting article from about 1954 about an experimental color tube that was rectangular with I believe an inline electron gun array. I might be wrong on the gun(s).

Like many folks, I prefer the round tube over the rectangular. I mentioned and RCA 8T-243 as an example of a set that I knew people could look up and I happen to have one. I always annoys me that like a year or two later RCA made pretty much the same set with a "double D" mask which to me makes for one heck of a better looking set. I also preferred round tube color sets back in the 80s when people were practically giving them away. I liked the look of the set in general better and in many cases I believe they produced a better picture. But then I am the type who would rather listen to my music on an LP as opposed to a CD, so go figure....

[bandersen]

I believe what he meant was that the first generation rectangular CRTs (16RP4) of the early 50s had squared off corners while the next generation (17BP4) were more rounded. I just happened to have one of each handy
Probably had to do with being able to use thinner glass with a more bulbous envelope.

[Tubejunke]

Perhaps you are right and that's an interesting comparison that I never noticed, or had examples of the two to see. I about 100% certain that both of those would be deemed rectangular in the Sylvania tube guide. Mine is buried in a box right now like so much of my electronics stuff these days.

I still wonder what the deal was with the first round of color tubes going back to round. Any thoughts on that anyone?

[egrand]

I think I read or saw somewhere that RCA would take a round screen with the color dots printed on them and would use a microscope to line up the shadow mask over them. Since they were round they could twist the shadow mask around to get it perfectly aligned. I guess at that time the machinery just wasn't precise enough to make a rectangular mask and screen without allowing for a little wiggle room. I think I also read that RCA had a very high reject rate as it was, maybe close to 50% early on.

I always figured the round picture was a compromise since they could have made it rectangular using a bigger CRT, but that would have made the sets much more expensive and heavier.

There could be some other technical reason too that I'm sure others know more about.

I have noticed watching some older color videotape programs from the late 50's and early 60's that at times the pictures have a lot of color fringing in the corners. Of course the engineers at the time couldn't have known that since their screens were round too. And, even if they did know it, they wouldn't have cared since nobody at home would see it.

[Electronic M]

The development of the first color CRT started in the early 50's when round monochrome tubes were still being put in sets. They chose a round tube early in development (the envelope of the 15GP22s developmental predecessor was basically a 16GP4).

Zenith demonstrated a 20" rectangular 15G based color CRT in 54' and Westinghouse had a small production of rectangular color sets in 1958(IIRC) so they could have been available earlier. My guess it that because of poor color TV sales prior to the mid 60's it was not worth the money to develop a rectangular CRT with comparable production economy of scale to the round tubes until then.

BTW IIRC broadcast color monitors had an under-scan mode to observe the edges and corners of the picture.

[StellarTV]

You're getting a few white lines on the screen intermittently? If they're in random spots and pretty bright, you probably have a failing damper tube. Try tapping it with a pencil or screwdriver handle or similar while the sets running. If the tube is bad you'll get lines shooting across the screen and probably sparks inside of the tube.

Also seen this problem with a bad rectifier tube / tube socket.