5AXP4 and 8XP4 as replacements?

[Bobby Dip]

Replacement picture tubes are harder to find than hen's teeth. But, the test tubes like the 5AXP4 and 8XP4 show up on eBay all the time. Can any of these test tubes be used as replacements? In other words, are there any TVs that the 5AXP4 would fit and function in as a replacement?

Bob D.

[Eric H]

There were no 5" magnetically deflected round tube sets that I know of.
The 8XP4 is physically similar to the 8DP4 used in the RCA portables of the mid 50's but those are so common there's really no need to find a substitute, I've never actuallt tried one in the RCA's so I don't know what the results would be, I expect it would make a picture since it's designed to be a universal sub.

Other differences I can think of offhand: Self Focusing, incompatible with magnetic and electrostatic focus.
No external coating.

[bandersen]

The documentation states they should not be used for extended periods of time. Not sure why though.

[Eric H]

Originally Posted by bandersen

The documentation states they should not be used for extended periods of time. Not sure why though.

Maybe since they only get used now and then they're not built to very high standards? Or there's a lot of stress on them running more high voltage than they would normally see for their size?

[Kevin Kuehn]

I've seen several that look like they have ion burn in the center.

Originally Posted by bandersen

The documentation states they should not be used for extended periods of time. Not sure why though.

Ion burn maybe? I recently picked up a Channel Master rebuilt 8XP4. For some reason it seems odd to me that they'd go to the trouble to rebuild a test CRT, but they did. Apparently something wore out on them.

The 5AXP4's seem hard to find for me.

[bandersen]

Right - ion burn. I just checked mine and they are not aluminized. They also use straight guns so you don't need to mess with an external magnet.

I see far more 8YP4s than 8XP4s or 5AXP4s.

[Eric H]

Both of my 5AXP4's have a small spot burned in the center, probably from being plugged in with the tube outside of the yoke so there's just a single spot on the screen.

[kvflyer]

Some of the test tubes that I have measure weak. And, a couple look as though they have gone to air and/or got water inside of them. They are for sure not of the quality of a production tube. I see imperfections in the phosphorus as well. However, if that is all that you have...

[dieseljeep]

Originally Posted by Bobby Dip

Replacement picture tubes are harder to find than hen's teeth. But, the test tubes like the 5AXP4 and 8XP4 show up on eBay all the time. Can any of these test tubes be used as replacements? In other words, are there any TVs that the 5AXP4 would fit and function in as a replacement?

Bob D.

I worked on an Emerson 8" TV radio combination, that someone replaced the CRT, with an 8XP4. It looked good enough.
I think the reason, they didn't recommend using test tubes as replacements, as the glass is thinner and more likely to implode.

[bandersen]

Seems unlikely they would make test tubes that are tossed around the workbench with no implosion protection with thinner glass. If anything I would think they are more rugged than convention CRTs.

[Fant]

Most yoke plugs have a B plus jumper so that if a TV is powered on without the yoke plugged in, there is no high voltage and no picture. If a chassis is connected to a CRT without the yoke plugged in and the high voltage comes, it will burn a spot in the center of the CRT.