|
|
|
#31
10-17-2007, 03:17 PM
|
||||
|
||||
|
Quote:
|
|
#32
10-18-2007, 08:26 AM
|
||||
|
||||
|
If a picture tube loses vacuum in an empty cabinet, does anyone hear it hiss?
The biggest problem with rebuilding CRTs that have gone to air is that the phosphor degrades.
__________________
Just look at those channels whiz on by. - Fred Sanford
|
|
#33
10-18-2007, 08:38 AM
|
||||
|
||||
|
If a picture tube loses vacuum in an empty cabinet, does anyone hear it hiss?
The biggest problem with rebuilding CRTs that have gone to air is that the phosphor degrades.
__________________
Just look at those channels whiz on by. - Fred Sanford
|
|
#34
10-18-2007, 11:53 AM
|
||||
|
||||
|
A broken CRT is always a sad thing to see. Also sad...in the early 90s I stored a CTC-15 with a good Channel Master rebuild. Just a few years ago I decided it was time to get the set going. I put the crt tester on it first and thought it odd that the filaments were glowing very dimly. I upped the voltage slightly and still they were not to full brightness. I thought something was wrong with the tester so tried another tube, and it was fine. So, I hooked the tester up again and, one by one, I watched the filaments burn out. The crt had gone to air over the course of 10 years.
I have one of those RCA test jig tubes with "Test Tube" etched on the face. It's a non-bonded 21" round color. I sure wish the etching wasn't there. I have heard others say it could be buffed out, but I don't know if I'll ever try it. The man I got it from had the jig a short while when he happened across a great deal on a then late model set with a broken crt, so he swapped this tube in and used it as his main home tv. Eventually he saved up for a new tube and put this one back in the jig.
__________________
Bryan
|
|
#35
10-18-2007, 11:54 AM
|
||||
|
||||
|
Quote:
In cases where the tube gets busted, either by a high voltage regulation problem (many Zeniths in the 70s, and in many newer projection sets,) you hear "Krack- HISSSSSSSSSsssssssssssssssss". If you snap the neck off, you hear "KSHTHWUPF" (Try to pronounce that  ) Charles
__________________
Collecting & restoring TVs in Los Angeles since age 10
|
| Audiokarma |
|
#37
10-18-2007, 09:10 PM
|
|||
|
|||
|
Quote:
__________________
julian
|
|
#38
11-03-2007, 12:52 AM
|
||||
|
||||
|
Quote:
There are different glasses and metals used in the manufacture of all CRTs. Each will have a different coefficient of expansion (rate at which physical dimensions change as heat is applied or removed). The trick is to match the coefficients between glass to metal or glass to glass so the different materials that are joined together have a similar coefficients of expansion. Otherwise, the materials joined expand at different rates and break apart from each other. The problem is compounded a bit with older CRTs. An old CRT has had time to "age" in a way that can affect chemical changes to glass to metal seal or glass to glass frit seals (15GP22 is a case in point) that may make it impossible to re-apply heat to those joints years down the road without causing them to fail. The secret to success is to find the minimum acceptable temperature and cycle time, or repetition of annealing cylces thereof, to safely anneal the join without inducing failure to other joints. A lot of experience and knowledge is necessary to determine the best cycling time and annealing temperature to achieve acceptable results so the tube won't fail. For the rebuilder it often means selecting a low temperature gradient and lengthened cycle time to minimize thermal shock. Annealing used during the rebuilding of a CRT is not the same as the annealing process used during the original manufacture. That's why most CRT rebuilders either discourage this business or avoid it entirely. They simply may not know the correct annealing parameters. This is not really the fault of the rebuilder - even the manufacturer may not know without extensive resaearch. What's really needed is an exceptional understand of the material science and chemistry of the problem. Two very difficult skill sets to find in any practitioner with a sound understanding of vacuum technique. The second reason to apply heat is to help the evacuation process. But this is a double edged sword. High heat destroys seals and may cause electrical feed throughs to fail. However, unlike the manufacturing process, the CRT rebuilder needs to take more time, often because the residual gas content of any old tube is hard to determine, unless RGA (residual gas analysis using a mass spectrometer is employed). This kind of anyalsis is often way beyond the ability of any rebuilder. Avoiding high "outgass" temperature is crucial to preventing implosion due to the mechanical failure of the envelope or failure of the seals. Typically in the world of restoration time is on our side. So, use the lowest heat possible and simply pump under vacumm for the longest possible time, and then seal the tube and flash the getter is often the best approach. Rebuilders who try to hurry the pumping process only short change the life of a rebuilt tube. Rebuilding any tube is really a process of situational awareness involving knowledge of structurual and chemical engineering. Hidden pitfalls lurk everywhere. Breathing life back into any old tube can be a unique challenge every time.
|
|
#40
11-03-2007, 01:59 PM
|
||||
|
||||
|
Actually, all conventional electron beam CRTs have some level of residual gas present in them, so in that sense they are filled, usually, with low levels of Hydrogen and Nitrogen gas, even small amounts of argon. But we're talking really low levels. Noble gases are usually always found several reasons, first, these gases are made from lighter elements in the periodic chart and can be often difficult for the getter to pump away. Second, they are typically stable and resisit breakdown, and thrid, slow leaks usually allow the lightest molecules to slip into the tube.
So called "gassy" tubes occur when very high residual gas levels are found inside the CRT. High residual gas pressures result in more significant collisions with electrons emitted from the electron gun of the tube. Gas molecules get in the way and collide with the electrons from the gun causing them to scatter, resulting in poor electron optics performance of the gun so fewer electrons focus onto the screen. Hence, we get a dim washed out picture. Sometimes you can peer through the neck of a CRT an see a purplish glow - usually indicated gassy conditions as the residual gas moelcules ionize in the present of high electric fields from the kinode. But, I suppose what you really meant was, has someone deliberately made a CRT that requires a "gas" to operate. Well, the plasma display is one such device, invented by Robert Wilson in 1964. Think about a CRT without scanning electrons and where each pixel is represented by an single CRT. A plasma display is made up of hundereds of thousands of tiny cells filled with Xenon or Neon gas. It takes hundresd of thousands of these cells just to make up the picture. There are other examples too - limited only by your imagination. 
|
| Audiokarma |
|
#41
11-03-2007, 05:04 PM
|
|||
|
|||
|
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.
|
|
#42
11-03-2007, 06:00 PM
|
||||
|
||||
|
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
|
|
#43
11-04-2007, 10:55 PM
|
||||
|
||||
|
Quote:
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! 
|
|
#44
11-05-2007, 05:58 AM
|
||||
|
||||
|
Quote:
Quote:
"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 Last edited by yagosaga; 11-05-2007 at 05:59 AM. Reason: Year added for the Fernsehheft
|
|
#45
11-05-2007, 01:29 PM
|
||||
|
||||
|
Quote:
__________________
tvontheporch.com
|
| Audiokarma |
 |
|
|
Linear Mode
