I'm curious-with the larger crts, did they take the same gun as what went into a 10bp4, for instance? If so, did that mean the 20" tube would wear out faster as the cathode had to emit more material to cover the larger screen area?

Voltage as well as current density affect brightness, so if the larger tube is run at a higher voltage, decent brightness could be produced without increasing cathode "loading". There is a limit to this, however, especially in un-aluminized crts.

jr

RACS rebuild is somewhere in the 750 Euro range for a Pyrex 20BP4. I was hoping people would get mobilized earlier this year while the dollar was strong so that the price wouldn't be so high in dollars, but alas that didn't happen and the dollar is falling now. So that's about $900-1000 at the moment for the rebuild.

RACS does a full rebuild with new phosphor and aluminization, so there is no problem with rebuilding tubes that have gone to air.

Shipping, if you try to ship just one tube yourself, is somewhere in the $600 - $1000 range. That's why we have plenty of incentive to pool. The total shipping price will be the same, pretty much regardless of the number of tubes, since it will be an overseas surface freight shipment on a pallet. It will be cheaper if we pool our tubes and ship from the east coast or Great Lakes region, rather than the west coast.

Obviously this isn't cheap, but if you have a valuable Pyrex tube to rebuild, it's the only game in town -- or more precisely, in the world.

Then would it be a good idea to have the 20BP4 re-built as an aluminized tube, rather than un-aluminized as the original?

jr

That's probably a matter of taste. I'll probably go with aluminized, but one could presumably have the option to choose no aluminization and bent gun for more historical authenticity.

Or, you could go for aluminization and bent gun. Some other CRTs were done that way for increased brightness, such as the 12LP4C. It still required a double field magnet.

The lower cathode current might mean longer life. Especially for a larger CRT like the 20BP4. Given the expense of rebuilding one that might be desirable.

John

*** Oops! Chuck pointed out that the 20BP4 is a straight gun to begin with. ***

Tom,

20BP4 is a straight gun, it's a screen burner. All of mine show ion burns on the screens.

Chuck

Mine has a big blast spot of missing phosphor in the center, so I think I never had an opportunity to notice the ion burn! :)

Aluminized sounds like the way to go.