cleaning CRT burn (was: an ADM-3A cam in tod...ay)

[Tony Duell]

> For the vintage computer collector though, replacing
> picture tubes is generally done with used tubes from
> something else. A lot of monochrome  tubes are pretty
> much interchangeable. Save junk terminals with decent
> tubes, they might come in handy. Also, don't overlook
> TV's - the picture tubes in 12" black and white TV's

I rememebr about 20 years ago I needed a new CRT for a somewhat rare 
(even then) terminal. After phoniug round a dozen CRT stockists, and 
getting the same story from every one ('12" black and white TVs are not 
worth repairing if the tube goes, so we don't stock them'), I finally 
realised the cheapest way to get a CRT (even then) was to buy a cheap TV 
and take the CRT out of it. Oh, and add some interesting components to 
the junk box as a by-product.

> make a pretty good replacement for many computers,
> I've used a TV tube in a TRS-80 Model III. Also, one
> time when I was bored, I transplanted the tube from an
> IBM 5151 display into a 12" Zenith black and white TV
> set. It worked fine, although the long persistance
> phosphor and WordPerfect screen burn made TV unusual.
> The things to look out for in swapping tubes is the
> physical mounting, the neck size, and base. Typically,
> if the base matches up, the yoke fits and you can bolt
> it in there, it should work. Modifying mountings is OK

In gneeral, for small mono CRTs, there are thin-neck ones with a modified 
B7G base (7 piu, the 'modification' being the seal-off tube in the 
centre) and a 12V-ish heater and thicker nexk ones with a B8H base (8 pin 
with a plastic locating hey in the middle round the seal-off tube) and a 
6.3V heater. Virtually all computer monitor/terminal CRTs have a 90 dgree 
deflection angle (some late-model portable TVs over here used 115 degree 
tubes, those are not useful in computer terminals).  And in each category 
they're pretty much interchangeable.  You may need to tweak the anode 
voltages to get the best picture, but it should work anyway.

-tony