Quote:
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
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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!
