If a picture tube loses its vacuum...

[peverett]

This is off the subject, but what Tom Ryan mentions about materials different rates of expansion when heated is exactly why I do not like the radiators in new cars(The ones with the plactic ends and aluminum body). After both my 70s Mustang and early 1980s Pickup truck(both with brass radiators) went 20+ years without the radiators leaking, my wifes crappy aluminum/plastic radiators starts leaking after 5 years. What crap.

[yagosaga]

Hi,

I know that the first German television sets from the first half of the 1930s used gassy picture tubes. Later they changed to high vacuum tubes. The Telefunken FE IV for example has a special gassy tube as documented in the original instruction manual.

- Eckhard

[Tom_Ryan]

Originally Posted by yagosaga

Hi,

I know that the first German television sets from the first half of the 1930s used gassy picture tubes. Later they changed to high vacuum tubes. The Telefunken FE IV for example has a special gassy tube as documented in the original instruction manual.

- Eckhard

The Early Television site lists the set you pictured as the SE-IV from 1935/38 as 180 lines. I'm not sure who's correct.

http://www.earlytelevision.org/telefunken.html


The FE-IV is a very different machine. Now, the FE-VI of 1938 is very interesting. Wow, looks as an RCA TRK-12. Seems pretty advanced for it's day. The Reich really had something. Makes one wonder if these sets were ever used during WWII. I know that the Germans had a TV station set up in occupied France at the Eiffel Tower as a demontration available for public. It would be historically interesting to get a hold of that stuff today.

There is one good thing to be said about a "gassy" tube. The ionization properties of a residual gas inside the CRT can be used in your favor to provide a source of electrons to help emission - but there are some side effects to consider. Historically, the Telefunken had 180 lines of resolution in their early TV sets. It was probably less than that using a gassy tube. A gassy tube would cause the divergence aperature of the electron beam from the gun to be very large. But, they probably didn't understand this too well back then. In addition to this, a gassy tubes would have produced a somewhat dim picture compared to the RCA TRK-12 of the same era (World's Fair 1939) due to a large amount of electron scattering from the residual gass inside the CRT. If you backfill a tube with a nobel gas (He, Ar , or Xe) or even Hg (mercury) it will ionize inside the tube, especially near the cathode and acts as a source of electrons. This allows for what's know as "cold" cathode emission. A great example of this is the 0Z4 full wave rectifier tube which does not have a hot filament but relies on the ionization of Ar (argon) to provide electron conduction to the anode. These tubes were extensively used in vibrator power supplies in car radios of the 1950's and early 60's. Another example would be mercury vapaor rectifiers often found in high voltage/ high current power supplies for transmitters. In the end, the Germans probably realized that to provide higher resolution and a brighter picture - the gassy tubes had to go! Enter the world of the hard vacuum and thermionic emission.

In another quirk of history, some 40 years later I remember Sony did some research in the 1980's using a cold cathode field emitter in their Chromatron color CRT. This predates the Trinitron and is technically very different. The Chromatron used a single electron gun so that the focused beam was sequencially switched to strike the correct phosphor color at the face of the tube. While similar to the Indextron, the high field intensities required to deflect the beam to the appropriate colored phosphor would often cause the aluminization of the phosphor screen to separate and short to the switching grid wires. As a result, the Chromatron was a nightmare for Sony service and nearly bankrupt the company...that is until they were rescued by the Trinitron!

[yagosaga]

Originally Posted by Tom_Ryan

The Early Television site lists the set you pictured as the SE-IV from 1935/38 as 180 lines. I'm not sure who's correct.

SE-IV is wrong spelling. It has to be FE-IV.

Originally Posted by Tom_Ryan

There is one good thing to be said about a "gassy" tube. The ionization properties of a residual gas inside the CRT can be used in your favor to provide a source of electrons to help emission - but there are some side effects to consider. Historically, the Telefunken had 180 lines of resolution in their early TV sets. It was probably less than that using a gassy tube. A gassy tube would cause the divergence aperature of the electron beam from the gun to be very large.

I cite the original source for the FE-IV:

"Mit so einem Strahlenbüschel kann man nur wenig beginnen, zumal dann, wenn als Ziel ein einziger Fleck erreicht werden muß. Wenn man in die vorhandene Glasröhre ein Edelgas, zum Beispiel Helium oder Argon füllt, so kann man eine scharfe Bündelung des Strahlenbüschels zu einem Strahl erzielen, wenn man den Heizfaden mit einem Metallzylinder umgibt, der mit einer negativen Vorspannung verbunden sein muß." (Das Fernsehheft, 1935, p. 27-28.)

Translation:

One can do with such a bunch of rays only a little, especially if one wants to get a sharp limited single spot on the screen. If one fills in the existing glass tube with a noble gas, for example, helium or argon, one can achieve a sharp focussed spot of the rays if one surrounds the filament with a metal cylinder which must be connected with a negative voltage.

The problem in these days was the focus of the cathode beam. They did not have proper electronic focus lenses. With the adjustment of the negative voltage for the metal cylinder, the beam was focussed on the screen.

In the later tv sets of the end of the 1930s (see for example the E1), they used electromagnetic coils for focussing the beam.

- Eckhard

[tubesrule]

Originally Posted by yagosaga

One can do with such a bunch of rays only a little, especially if one wants to get a sharp limited single spot on the screen. If one fills in the existing glass tube with a noble gas, for example, helium or argon, one can achieve a sharp focussed spot of the rays if one surrounds the filament with a metal cylinder which must be connected with a negative voltage.

The problem in these days was the focus of the cathode beam. They did not have proper electronic focus lenses. With the adjustment of the negative voltage for the metal cylinder, the beam was focussed on the screen.

In the later tv sets of the end of the 1930s (see for example the E1), they used electromagnetic coils for focussing the beam.

- Eckhard

Eckhard is correct on this. Most crt's in the 1920's and early 30's were of the gassy type. The gas was actually used to focus the electron beam as there was no good way to focus it in a hard vacuum type tube at the time. While this worked fine for oscilloscopes and such test equipment, gassy tubes are not very suitable for use in television. A gassy tube can only be focused over a narrow band of beam currents. Since the beam current needs to be modulated for television, this resulted in poor focus.

Zworykin while working at Westinghouse in 1929 developed and patented the first hard vacuum crt with an electronic lens. This is what he called the "kinescope" and is the basis for all modern crt's. It is said that most experts of the time scoffed that this was impossible, and RCA did not publicly show the kinescope until May of 1932, and then only to RCA licensees.

Darryl

[yagosaga]

Originally Posted by tubesrule

While this worked fine for oscilloscopes and such test equipment, gassy tubes are not very suitable for use in television. A gassy tube can only be focused over a narrow band of beam currents. Since the beam current needs to be modulated for television, this resulted in poor focus.

Hi Darryl, these early German gassy picture tubes were used up to 1936. From 1937 and later the CRTs were high vacuum tubes.

In a gassy tube the negative voltage at the metal cylinder was adjusted for a focussed beam with maximum brightness. When the beam current was lower or low, the focus became poor, and as a result, the point on the screen became darker. In this way, one effect of the gassy tube was an improvement of contrast, but a loss of gradation.

The high vacuum tubes generated a more natural b/w picture with an improvement in gray tones and gradation.

- Eckhard

[David Roper]

Originally Posted by Tom_Ryan

I remember Sony did some research in the 1980's using a cold cathode field emitter in their Chromatron color CRT. This predates the Trinitron and is technically very different...the Chromatron was a nightmare for Sony service and nearly bankrupt the company...that is until they were rescued by the Trinitron!

Chronology off...by 20 years or so? We had Trinitron sets all through the 70s and early 80s starting from about '71 on.

[zenith2134]

Just for the record, what kind of temps are we talking about and what type of oven is this in? I sure hope there aren't people trying this in their typical Tappan oven....

By the way I have found this thread very interesting and have learned much from it. Thank you.

[hposter]

With all of this interest in CRT rebuilding, it begs the question, why doesn't anyone want to experiment?

Twice over the course of the last 15 years, I've been offered CRT rebuilding stations from defunct shops, and I've have never found any one willing to buy and/or pickup the equipment. One offer to me was for a free set-up (Come and get it!), and the other was for about $1,000 or $2,000.

I also remember one or more set-ups offered on ebay in the last 5 or 6 years.

I always wished I could make the room, and the time, but if I had taken any of these, they'd still be kicking them around in the back of my garage!