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Author Topic: Reliable loose plate cap to glass cement for old amplifier tubes (811A, 572B)?  (Read 1286 times)
N6QWP
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Posts: 164




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« on: September 06, 2017, 03:49:41 PM »

Looking for tried and true cements for gluing loose plate caps back to the glass envelope of tubes. 

Able to withstand the high heat fluctuations of amplifier tubes over time? 

Successes?  Failures? 

Thanx
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CHUCK49
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« Reply #1 on: September 06, 2017, 07:22:55 PM »

There are a couple of things to try (some may be overkill!)

Sauereisen Ceramic Cement No. 8, Good to 2600 deg F, 4oz Jar of powder is $13.50, available here: http://www.sisweb.com/ms/scc.htm#2

Masterbond MB600SCN, Good to 700 deg F, have to purchase from manufacturer:
https://www.masterbond.com/tds/mb600scn

Permatex High-Temp Red RTV Silicone Gasket Maker, Good to 650 deg F, available at most auto parts stores.
https://www.permatex.com/products/gasketing/gasket-makers/permatex-high-temp-red-rtv-silicone-gasket/

Hope this helps...
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N6QWP
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« Reply #2 on: September 06, 2017, 08:17:53 PM »

Thanx for those recommendations.  Wondering what temperature 811A tubes can get to when driven to their limit?  The Permatex would be the easiest to acquire....but will it hold up at sustained operating temps?

Only have one tube that has this problem at the moment.....but expect with old tubes that I will encounter more in the future.
« Last Edit: September 06, 2017, 08:19:59 PM by N6QWP » Logged
KH6AQ
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Posts: 7696




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« Reply #3 on: September 06, 2017, 10:25:16 PM »

I recall reading somewhere a rather low maximum glass temperature of 200 deg C. I'll see if I can find the source.
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KB4QAA
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« Reply #4 on: September 07, 2017, 06:32:26 PM »

Another alternative is 'furnace cement" a high temperature, quick setting cement used to seal furnace flues to chimneys.
https://www.walmart.com/ip/Imperial-KK0077-A-Furnace-Cement-236-ml-Tub-Black-Thick-Paste/41128545?wmlspartner=wlpa&selectedSellerId=282&adid=22222222227028773895&wl0=&wl1=g&wl2=c&wl3=61538001249&wl4=pla-97479093609&wl5=1018531&wl6=&wl7=&wl8=&wl9=pla&wl10=111838817&wl11=online&wl12=41128545&wl13=&veh=sem

Many hams have reported good success with JB Weld.

« Last Edit: September 07, 2017, 06:37:40 PM by KB4QAA » Logged
AD4U
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Posts: 2432




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« Reply #5 on: September 08, 2017, 07:21:39 AM »

Over 10 years ago I glued a loose cap back on a 8950 tube with JB Weld.The 8950 tube is in a Swan 700 transceiver in my boat anchor collection. After 10 years the cap is still glued to the glass tube.

Dick AD4U
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N2DTS
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« Reply #6 on: September 08, 2017, 10:17:02 AM »

The red high temp permatex will not hold, its soft.
Its like any other rtv type sealant, its not a glue/cement.
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N6QWP
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« Reply #7 on: September 09, 2017, 05:37:07 PM »

That was my reservation.....thanx.  JB weld seems to be interesting.
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KM1H
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« Reply #8 on: September 11, 2017, 04:56:28 PM »

Ive been using the old style furnace cement for over 50 years on tubes and furnaces, why buy something new?

Carl
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W4IJ
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« Reply #9 on: September 13, 2017, 01:08:34 PM »

The Walmart furnace cement is good to 1093C, or 2000F.  I've used it successfully.   Hard to beat the price.
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N6QWP
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« Reply #10 on: September 13, 2017, 04:11:56 PM »

Thanx for the recommendations.  Seems that furnace cement is the choice so far....less yucky to deal with than JB weld.
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KD8IIC
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« Reply #11 on: September 15, 2017, 11:26:23 PM »

  Just how often are we planning to remove the plate cap wire anyway??? 
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