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  #31  
Old 05-29-2013, 08:21 PM
Geoff Bourquin Geoff Bourquin is offline
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Regarding h/k assemblies for rebuilding old guns, it appears they are in very limited supply. Does anyone know if it might be possible to use h/k's from modern CRTs? It has been pointed out that there are guns available for modern tubes but nobody has any use for them. Would it be possible to remove the heater/cathodes from these guns and mount them in place of expired ones on vintage guns? I realize this is a long shot, but it never hurts to toss out an idea. Worst thing that happens if everyone laughs at the dumb guy, right?
Another thought, what about getting guns from Asia? I understand someone is still making CRTs for use in some parts of the world. Maybe a they could make a supply of guns for our old B&W tubes. (I know..probably even dumber, and expensive idea)

Last edited by Geoff Bourquin; 05-29-2013 at 08:23 PM. Reason: The dumb guy can't spell!
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  #32  
Old 05-30-2013, 01:11 AM
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ppppenguin ppppenguin is offline
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When you let a CRT down to air the cathode's emissive surface is wrecked. A new cathode is coated with (I think) a carbonate whch is converted to an oxide during pumping using an RF heater. I'm sure somebody will correct me if I'm wrong.

I don't think it would be feasible to transfer a cathode from one CRT to another entirely in vacuo.
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  #33  
Old 05-30-2013, 06:38 PM
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I believe you are correct, it is activated once all the vacuuming getting and baking is done.
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  #34  
Old 05-30-2013, 07:25 PM
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Yes, that is correct, but if you are starting with a cathode taken from a new gun intended for a modern tube, then the cathode should still be unactivated, as the gun was never sealed into a tube. The activation of the cathode takes place while the tube is being pumped down, so that the liberated gases can be removed from the tube. The getter is fired once the tube is sealed off from the pump.

It seems highly unlikely that a modern cathode assembly would mechanically fit the older guns, though. The cathode/grid spacing is highly critical for proper cutoff, with tolerances measured in thousandths of an inch.
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  #35  
Old 05-30-2013, 09:14 PM
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Activating the cathode after pinch off won't poison the tube, I suspect they were activated during bake out to save processing time.
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  #36  
Old 05-30-2013, 10:45 PM
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As I understand it, there are 2 distinct processes: "Breakdown" is done on the pump station and is achieved by ramping up the heater voltage to remove the binder used when the Barium Carbonate material is sprayed onto the Nickel cathode surface, as well as Carbon Monoxide from the Carbonate. Both heater voltage *and* RF induction heating are involved in this process. "Activation" , the second process is done after the tube is sealed off and the getter is flashed, and involves ramping up the heater voltage *and* drawing current from the cathode, to create stable emission sites on the very surface of the cathode. After current is drawn for some length of time, the heater voltage is brought down to "normal" voltage, and operated there for a while, a "slump test" may be performed to determine the stability of the cathode emission.
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  #37  
Old 05-31-2013, 02:00 AM
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Not sure about the terminology. There are certainly 2 steps, one during pumping, the other afterwards.

During pumping the cothode is heated with the RF coil (didn't think the heater was needed too but I could be wrong) and the carbonate is converted to oxide. I would imagine this is best done before the tube is sealed off because it liberates some gases.

After it's sealed off and cooled down then you draw current from the cathode to increase and stabilise the emission. For the EMI 6/6 that was rebuilt in 1986 I did this for my first and, so far, only time. I had no idea what sort of voltages and currents to use so I erred on the side of caution. The result was that the initial image on the rebuilt CRT was disappointing. After a couple of hours running in the set the picture improved hugely, to the best and brightest that I have ever seen from one of these CRTs.

Cathodes also seem to get "tired" from long periods of non-use. Again a few hours running usually improves things
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  #38  
Old 06-17-2013, 11:30 AM
7jp4-guy 7jp4-guy is offline
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Well here is one hard datapoint. A used-but-tests-good 10FP4 just sold on eBay for $227.75.

-Matthew
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  #39  
Old 06-19-2013, 03:26 PM
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colorfixer colorfixer is offline
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One thing: If RACS has guns for the specific early 80's color CRTs like the M48AAW00X, 19VJTP22, and the 19VLUP22 used in color XY (and a few raster) arcade games could be a potential source of income for the project. I'd think these being "modern" should mean that they're able to be done with a high yield.

I've been searching for new or good M48AAW00X's for a long time -its limited use (high resolution) makes it difficult to replace. The 19VLUP22 is hard to sub because of its 100 degree deflection angle.
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  #40  
Old 06-21-2013, 07:25 AM
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jhalphen jhalphen is offline
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Hello ColorFixer,

I've queried RACS about their having in stock new ready to mount guns for the 3 CRT references you quote in your message.

Will post reply when i get one.

I have also queried them about what equipment/glass/parts they may recycle soon - planned date given months ago was July 2013. Have requested detailed itemized list and prices.

Best Regards
jhalphen
Paris/France
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  #41  
Old 06-21-2013, 12:42 PM
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colorfixer colorfixer is offline
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Thanks Jerome.
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  #42  
Old 07-23-2013, 10:06 AM
7jp4-guy 7jp4-guy is offline
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I think colorfixer has a great point - there may be a market for 'newer' CRTs as well as 'vintage' ones. For example, new CRTs for HP 8591 spectrum analyzers (and similar) are selling well at $195 each:

http://www.ebay.com/itm/NEW-CRT-HP-A...item20be07ace8

-Matthew
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  #43  
Old 07-23-2013, 11:06 AM
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dtvmcdonald dtvmcdonald is offline
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I suspect that in the future the ultimate will be the tubes
for Tektronix 454 and 455 scopes, possibly the higher end 7000 series too.

There really would be no way to fix one of these short of replacing just
the cathode, the gun is so complex.

And there is simply still no digital substitute for some uses for these.

Doug McDonald
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  #44  
Old 07-23-2013, 12:41 PM
7jp4-guy 7jp4-guy is offline
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Good point. Also, don't forget the 2445/2465 series. As the 'last and best' analog oscilloscope these things are still used professionally. In our lab alone (at MIT) we must have at least a half dozen.

-Matthew
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  #45  
Old 07-23-2013, 01:05 PM
WISCOJIM WISCOJIM is offline
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I thought VDC was still doing medical, military, and industrial CRT rebuilding. I thought they only got out of the non-profitable consumer CRT rebuilding.

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