I am new to this forum and from the UK. As colour transmissions didn't start here until 1967 we didn't have round CRTs used in production TVs. When I see pictures of round screen TVs working I often wonder if the round cut off in the corners actually hide part of the broadcasted picture. As the NTSC standard was monochrome compatible and I presume that US Monochrome CRTs of the same period where rectangular (as in the UK) then the round colour tubes must have been missing some of the transmitted picture? Would this be apparent if displaying a modern test pattern?

I am asking because I am about to start bringing a "experimental" Thorn round tube TV back to life. It belonged to my dad who was part of the R & D team for Thorn. Built originally in 1961 as a 405 line VHF NTSC all valve receiver but converted to a 625 UHF NTSC one and in 1964 to a 405/625 VHF/UHF simple PAL hybrid set. Thorn then decided that they wanted a rectangular receiver ready for the launch, and they produced a 19/25inch dual standard chassis that was the first all transistor chassis in production thoughout the world. it was known as the 2000.

We used the round tube at home for a year from 1967. It then went into storage, I am about to pull it out together with the documents and the spare RCA tube, Valves and boards that came with it. Although to tube was a US RCA one. the rest of the set was totally home grown so I have no idea as yet as what a can of worms I will be opening. I do remember that It had a hue control that had to be used often and it worked faultlessly for the year we used it at home. It went into storage fully working and was replaced with a 25 inch pre-production Thorn 2000 chassis. Things moved fast back then, The next chassis the 3000 was produced and the new squarer 22 and 26 inch tubes were ready to go! Just in time for the full colour launch in 1969!

Yes, part of the picture (in the 4 corners) will be cut off when the horizontal and verticle geometry of the screen is set up correctly. This is true for all round screen tv sets, both black and white or color.

...

Yes, part of the picture (in the 4 corners) will be cut off when the horizontal and verticle geometry of the screen is set up correctly. This is true for all round screen tv sets, both black and white or color.

The "safe title area" used to be the inner 80% of width and height, but modern TV sets are much more consistent on overscan (usually 3% or so), so it's not as critical.

I think I have seen a picture of a viewfinder with the round tube outline drawn on it, but maybe someone who was involved with early color production can say yea or nay.

Welcome to VK !

I would be interested in hearing more about the Thorn 2000. I've always read that the Motorola Quasar was the world's first production solid state color TV, but American publications tend to ignore foreign accomplishments (particularly in the late 60's when the US was at the center of the universe).

The 2000 chassis was introduced in 1967 and was fully SS except for the CRT, the US set you are talking about had a glass rectifier valve.

The 2000 had development problems when it came to the HV side if things, The best and newest transistors (from the US) were expensive at $15.00. a shot and in development thorn were blowing out many hundreds a day - until the got the circuits perfected! It was a very popular set at the launch, so-so picture but a world beater (according to the press of the time).

I will try to dig out some of the original paperwork and publish it, but this interesting site gives an insight to the Thorn 2000 chassis and all the different models produced. Plus some of the other makers sets of that period.http://www.oldtechnology.net/colour.html

I'm sure a CT-100 or 2 found their way Across the Pond to our cousins in Old Albion- 'Twould be interesting to know the stories on them. Betcha the Germans & the French scarfed a few CT-100s, too, as well as the Italians & Rooskies, too...Must have stuck in ol' Kruschev's craw a bit that so much of the work on TV was done by emigre Russians living in America...

The 2000 chassis was introduced in 1967 and was fully SS except for the CRT, the US set you are talking about had a glass rectifier valve.


What sort of high voltage rectifier was used, do you know? When I joined Motorola in 1966 they were working on the solid state chassis (I wasn't directly involved), and they used a single solid state rectifier assembly that consisted of a stack of several hundred "high" voltage rated diodes (perhaps 1kv each). The asembly had curved side fins to equalize the capacitive current among the diodes from the top to the bottom of the stack. The units were made by Varo in Texas.

I don't know how long Motorola used tube rectifiers, but my impression is that it was just a stopgap while the solid state rectifiers were being perfected.

Greetings and welcome to VideoKarma. I hope to follow this interesting thread.

On some round B&W TV's (Zenith) customer could switch to reduced scan.
( Slideswitch in pencilcase )

What sort of high voltage rectifier was used, do you know? When I joined Motorola in 1966 they were working on the solid state chassis (I wasn't directly involved), and they used a single solid state rectifier assembly that consisted of a stack of several hundred "high" voltage rated diodes (perhaps 1kv each). The asembly had curved side fins to equalize the capacitive current among the diodes from the top to the bottom of the stack. The units were made by Varo in Texas.

I don't know how long Motorola used tube rectifiers, but my impression is that it was just a stopgap while the solid state rectifiers were being perfected.

Off hand I have no idea, and I will have to get the service manuals out of storage. The Christmas holiday has become rather extended in the UK and for most non-retail operations extend thru to the 3rd January! That includes my storage facility.

I spent an hour or two reading through my dads Journals this morning and I am learning some interesting things about some interesting Anglo/USA connections. In 1955 Thorn and Sylvania set up a CRT plant in the UK, in 1956 they formed the Sylvania Thorn colour TV labs here. and before 1967 Thorn were importing the Glass CRT bulbs from the USA for the original run of CTV tubes and building them here. Dad also mentions co-operation between Thorn and RCA in the mid 60s (have not found out what for as yet).
Those Line output / EHT state of the art transistors were Texas R2009.

No round tube CTVs were ever marketed in the UK as by 1967 rectangular tubes were the norm here, BUT dad did say that it is possible that some rebranded USA round tube sets were actually imported, modified for PAL UHF 625 line 240 volt 50 hz.. and put on the rental market?

...

I think "all solid state" means no tubes except the CRT; with a HV rectifier tube I'd call it solid state* (with an asterisk). Tubes in the sweeps makes it a "hybrid," of which there were many examples until all-solid-state became cheaper.

Back then in the UK we would have not used "solid State" as a descriptive, probably "all Transistor" or even "fully transistorised" and in the mid sixties we had very high import taxes so very little was coming in from the far east or the USA. Electronics with Solid state on the front, such as, say an Akai tape deck just would not have been in the UK. US and Jap electronics and electrical produce never appeared in the UK, even the Sony Corp from Japan could not get a foot in the door with their colour TVs without using a non PAL decoder and not having to pay Telefunken the royalties.

Thorn very early on realised that Transistors meant more profit and as the biggest electronics company here they had stopped using the Valve in 1966, No way were they going to put any in their CTVs! As the biggest tv rental company here as well, transistors meant reliability and less service call outs. Once again more profits!

The "safe title area" used to be the inner 80% of width and height, but modern TV sets are much more consistent on overscan (usually 3% or so), so it's not as critical.

I think I have seen a picture of a viewfinder with the round tube outline drawn on it, but maybe someone who was involved with early color production can say yea or nay.

Back in the mid '60's when rectangular color tubes were being introduced and our control room monitors were still roundies, we were very careful not to cut off any graphics and that the sponsor's product was centered in the frame. This applied to any image that included tight head shots to wide master shots. Roundie color sets were a consideration for many years after the intro of the rectangular sets. I don't recall the camera viewfinders having cutoff lines marked on the crts. The director could determine the framing. This refers to live & videotape. I assume those working with film for tv did the same.

-Steve D.

Back in the mid '60's when rectangular color tubes were being introduced and our control room monitors were still roundies, we were very careful not to cut off any graphics and that the sponsor's product was centered in the frame. .

I've seen evidence that some producers do this today, with respect to being sure graphics dont get cropped off by DTV converter boxes displaying a cropped 16:9 HD image to 4:3 NTSC. I've also seen where they didn't worry about it, one network shows the football game score in the upper left corner, and it partiallly gets cropped.

Let's see some pictures of all of them esp the round tube!!