Just aquired a trk-12
 

Hello,

I just acquired a trk-12 that was recently on ebay. Unfortunately the crt has gone to air via the HV cap. The rest of the set is nice and original.

I found this company that claims they can rebuild any crt...

http://www.thomaselectronics.com/

is anyone familiar with them?

Best Regards

Bill A.

I'm not familiar with them, but if they are willing work on to your tube make sure they know that it is made of Pyrex glass which cannot be directly joined to the glass formulation used in modern CRTs (without joint cracking upon cooling).

Thomas Electronics is primarily a defense/aerospace contractor, so be prepared for pricing in line with the $800 hammer/$1000 toilet seat crowd they usually sell to.

That's assuming they will even do the job...

Bill,

Don't hold your breath. There isn't anyone out there that has been able to rebuild the old pyrex glass bulbs in a long time. RACS in France was trying to do it a year or so ago, but every one that they did developed cracks around the anode cap and went to air in a short time.

There are many of us collectors with multiple tubes that have gone to air, and would pay dearly for someone to rebuild them. If you decide to follow up with them keep us informed.

Chuck

Thomas has said in the past that they would try a prewar tube from a British collector.

I haven't heard of any progress in quite some time.

I've let the British collector know about this thread so hopefully he can update us on this effort.

Darryl

I saw a piece at the ETF about replacing them with radar tubes.
IF that does not work, looking at the picture of the real thing,
fixing the anode should be very easy for any glassblower.
Just remove the dag coating in the vicinity of it, remove the old one
by glassblowing, and replace it with a standard pyrex stem HV feedthrough.
Then apply new dag to connect it up.

The problem is of course getting rid of corona at the HV
connection at the outside, but I never had difficulty even
at 15 kV with such feedthroughs.

The neck of course would need a graded glass coupling to
a new gun, and baking would have to be
done at a bit lower temp for longer.


DOES the ETF have any more radar tubes?

I think the radar tube you are referring to is the one used in this:

http://www.earlytelevision.org/12ap4_substitute.html

Even if more shells could be found there is presently no company that will turn them into P4 tubes.

The graded seal method has been done successfully in the past, but, again, there is no one around to do it now.

RACS had problems with cracking around the anode connection when they baked the pyrex tubes and gave up on doing them.

I am convinced that with the right glass and some experimenting that we will be able to rebuild prewar tubes someday. But that is months or years away.

Its easy to learn enough glassblowing for you or whoever you hie
to do replace the anode button with a "wire" feedthrough and
install a graded seal. Getting a close enough graded seal may
be the problem.

Respectfully, if it were so easy lots of people would be rebuilding prewar tubes...

Its not a matter of "ease".

Its a matter of "very custom" and "big bucks".

With big bucks one could even dispense with a graded seal
by attaching the gun to a Pyrex based pin base or use a custom
array of pyrex to metal seals. That last method is absolutely guaranteed
to work and is easy for a good glassblower, but not cheap. You would
of course need to use loose socket pins on a custom PC board.
I have actually used such devices. Its common in the scientific field.
You just have to think outside the box, and damn the inauthenticity.
You'd end up with an all-Pyrex tube, a good thing.

dtmcdonald, rebuilding a CRT is a complicated multi-step process. Replacement guns are no longer available, so old ones must be rebuilt. Replacement cathodes, heaters and spacers may not be available. Pyrex tubes introduce more issues.

Take a look at these links to see what is involved:

http://antiquetvguy.com/Web%20Pages/...ie%20Page.html

http://www.earlytelevision.org/pdf/C...t_williams.pdf

We are attempting to set up a facility to do it, but there are many issues that still remain:

http://www.earlytelevision.org/crt_project.html

Pyrex is clearly a very late step, after all else is working
well.

I had a 12AP4 at RACS for rebuild that cracked. The original intent was to have Pyrex stems made so no graded glass would be required. They quickly found the Pyrex stems were experiencing micro-cracking around the leads. After a few failed attempts they gave up and went with a soft stem and a graded ring. This appeared to be working in the first couple of tubes, but then cracks started appearing around the HV lead. These tubes don't use a button like a modern crt but just a lead exiting the envelope, just like the stems that were cracking. They were supposed to send my crt to a lab in Paris for failure analysis but this was just as things were coming to and end at RACS, and that never happened.

They never did determine exactly what was causing the cracking. Was it when the envelope was first opened and the stress relieved? Was it during baking? Was it during pulldown? Hopefully we will have a chance to experiment ourselves at the ETF, but there are only so many duds to experiment with. Perhaps we can persuade John Y who has been doing fantastic work on the 15G's to do some research on the Pyrex tubes so we have a better understanding of what's going on there.

RACS also mentioned the problem with Pyrex is getting the exact formula correct, and not knowing exactly what the original formula used for the crt glass was. These tubes were rebuilt by RCA back in the 40'a and 50's as there are a few floating around, so it was possible at one time, but that knowledge has been lost.

Here's my 12AP4 after rebuild before it started going down to air. So close....

I wonder if installing a HV button with frit-glass might work on those pre-war tubes.