Re-attaching 811 plate contacts

[KA1ZGC]

Hey Guys,

I have the worst luck with 811s.

I pulled the toobz out of the Junkyard Dawg a little while ago, and when I pulled the plate cap off one of the 811s, the contact came right off the envelope, leaving just a piece of wire sticking out of the top of the glass.

The seal is still good, and it looks like I can re-solder it, but I'm wondering if there's anything else I can do at this point to help the situation.

Any caveats or helpful hints you guys can pass along? I've never done this before, and I'm wondering if there's anything I can do to help re-seat the cap so it's less inclined to pull off from the envelope in the future.

Thanks in advance.

--Thom

[Ed-VA3ES]

Prep the plate cap in he following manner:   Get some J-B Weld.  Prep the solder hole in the cap by cleaning it out.   Put a very small amount of the J-B Weld  on the bottom of the cap.  Solder the cap to the wire, and press the cap down to force the J-B Weld onto the envelope.  (You may have to scrape the extra J-B Weld off).  Wait about 24  hours.    Done.

J-B Weld is highly heat resistant.

[K1DEU]

I have cleaned the Glass and dug and scraped out the plate cap. Then used Crazy Glue curing in a 70 degree room about an hour. Many times before, John

[WBear2GCR]

I've been told that the flowable silicone rubber works ok fine here...
I have yet to try it.
They sell it at auto parts stores for windshield repairs among other uses.

It works fine and dandy on loose bases for sure, that I've tried.

          _-_-Wombat Bear Two Goats Cougars Raptors

[W2JBL]

  none of the consumer grade epoxies, "crazy glues" or silicone sealers can stand the kind of heat dished out by a hot tube in a big maul. i use furnace cement, just like we use to patch holes on woodoline stoves. it's water based, and cures best when heated. it also bonds really well to glass. comes in little tubs like margarine from the hardware store. as mentioned above clean everything nice like a good boy scout, especially the wire coming out the top of the tube so you get a nice slobber connection. the stuff its truly excellent for re-gluing tube bases too in case you get a bit hammy handed yankin' those bottles out of their sockets. best of all it won't burn. i have spots on my woodoline stove patched with it that run near red hot and have held over ten years.

[W7SOE]

I would send you some "refractory mortar" that I have but the envelope would bust open at the post office and I would spend the rest of my days at Guantanamo.   

Rich

[Carl WA1KPD]

I have had trouble with some tubes breaking at the top after using "Crazy Glue" type material. I understand that the cure process can involve very high momentary heat that weakens the glass.
YMMV
Carl /KPD

[The Slab Bacon]

FWIW, I have been using "krazy Glue" to reatach loose plate caps and tube bases for years and never had any problems. Many of the 2 part epoxies seem to soften with heat. Like others have said YMMV.
                                                         The Slab Bacon

[Carl WA1KPD]

FWIW, I have been using "krazy Glue" to reatach loose plate caps and tube bases for years and never had any problems. Many of the 2 part epoxies seem to soften with heat. Like others have said YMMV.
                                                         The Slab Bacon

I often use the acceleration spray with it. Maybe that is the issue?

[WBear2GCR]

My limited understanding is that there is more than one type of refractory cement...

Wonder which type(s) are good with metal and glass?
Brands?

Uncle Tim's Olde Tyme Gook??

                                    _-_-woobly bearing two grainy crunchy reamers

[Steve - WB3HUZ]

Just use a clip lead. You don't need no plate cap.

[KD6VXI]

Just use a clip lead. You don't need no plate cap.

I was thinking about this last night, and wondered if the liquid porcelain would work.  My Mom used to buy it when she was working with glass, and it seemed to work nicely.

Seems heat resistant, a good insulator, and cures in a decent amount of time. 

Any ideas from those with more knowlege?  Stained glass shops (and others) had these in the past.

--Shane

[Carl WA1KPD]

Just use a clip lead. You don't need no plate cap.

Clip lead?
I just remove the twist the wire to the  together with the plate lead

[KL7OF]

You can solder the lead on and unsolder it when the tube needs to be replaced....  I wonder what kind of stuff the tube manufacturer used to fill up the void in the cap originally?

[KA1ZGC]

TNX fer all the suggestions, guys.

For the moment, the cap has been slobbered back on to the lead. Nothing else has been done. I'll be pulling that tube again in the near future, and I'm sure it'll yank back off from there again, so I'll get the chance to try out some of these suggestions.

I've often wondered what that brown cruddoline is they filled those caps with when they jammed them on the top of the tube. Probably nothing I want to play around with.

I can't go the clip-lead route because the tube is within an inch of the blower for the RF deck. Slobbering to the plate lead isn't an option because I need to pull those tubes to safely pull the RF deck (they're taller than the modulator chassis).

I'll be picking up some more 811s (and 4-250s, 4-400s, etc.) during the hamfest season, but I need to keep this one alive (and removable) until then. I plan to do more work to this transmitter during the spring and summer months.

For now, it's fresh slobber and a prayer. When I revisit this problem, I'll give a stab at some of your ideas.

Thanks a bunch, guys.

--Thom
Killer Agony One Zipper Got Caught

[w1vtp]

Any caveats or helpful hints you guys can pass along? I've never done this before, and I'm wondering if there's anything I can do to help re-seat the cap so it's less inclined to pull off from the envelope in the future.

Thanks in advance.

--Thom

Actually, I have been thinking of Fahnestock clips for this kind of problem.  Why stress a perfectly good 811A?  You could have two sets of plate connections -- with and without plate caps.  I think we all know better than to have our hands near this stuff when the HV's on.  You could say the plate caps are eye candy.

http://www.sargentwelch.com/product.asp_Q_pn_E_WLS31067-05_PK_A_Fahnestock+Clip+Connectors_E_

Al, VTP  See you on Yay YM

[WBear2GCR]

The wire coming out of the glass is fairly brittle, that's why you don't want to flex it or have it vibrate with a solid clip or solder joint - it needs stress relief, thus the plate cap.

Tubes with the thick wire out the top, 3-500Z for example you do connect directly to the plate wire, eh? 

The brown crud under that plate cap is just "lamp cement".
It's a phenolic based cement.

Look it up on Wikipedia!! 

Not dangerous at all...

                _-_-bear