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Old 30th December 2009, 03:13 PM   #1
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Default Loose Tube Bases

I have an NOS quad of 6B4's but 3 of them have slightly loose bases.
Does anyone know how to fix this?
Can I dribble some super glue into the joint?

I searched the internet and this forum without happy results.

Thanks.
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Old 30th December 2009, 03:49 PM   #2
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I believe the original glue that was used in this application was phenol-formaldehyde, or 'recorcinal' adhesive. It's a brown powder into which a dark red catalyst is mixed. Dries slow, heat helps cure it, and it's pretty impervious to heat.

If I am in fact mistaken, it will be in lieu of another similar adhesive, urea formaldehyde, or 'plastic resin' glue. The original WeldWood. This is a light brown powder that is mixed with water. Very similar properties to recorcinal glue.

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Old 30th December 2009, 03:53 PM   #3
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This recipe for RCA's basing cement, yielding about 200 pounds of material, was "standard for all bases.":

Coarse marble flour 170 lb.
Orange flake shellac 19-1/2 lb.
Durite phenolic resin LR275-2 7-1/2 lb.
Medium-color (grade G) rosin 3-1/4 lb.
Denatured alcohol 9 liters
Malachite Green aniline dye 10 g.

(Just for reference: the above recipe yielded enough cement to put bases on 23,000 Type 50 tubes

The AWA Journal - The Vacuum Tube

Never would have guessed, myself.
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Old 30th December 2009, 04:05 PM   #4
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Quote:
Can I dribble some super glue into the joint?
Yes. Or nail polish.

Loose Bases.

To re-cement the tube, use clear nail polish - paint a ring around the base, let the polish soak into the old cement, recoat, and let dry overnight. Polystyrene "coil dope" works as well, and can be used to refill the nail-polish bottle.

Solvent (acetone, etc.) are ineffective in softening the old base cement - the cement was baked hard in manufacture, and "nothing" dissolves it.
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Old 30th December 2009, 04:06 PM   #5
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I've used superglue with some limited success.. Limited in the sense that the tubes were small signal triodes (UX4 base) that don't get very warm in operation, and they are tubes I didn't particularly care about.

In higher temperature applications I am not sure what would happen - perhaps it would work, perhaps the glue would quickly fail, or perhaps the stress on the envelope due to the glue (non matching coefficient of expansion) might cause the envelope to crack.

IMO Removing the base in order to use a diy mix of basing cement is a bad idea - no guarantee that you will get it apart & back together without damaging the tube, not the least of which is the leads have been trimmed back after soldering and it may hard to assure long term integrity of the solder joint if you are not good at soldering tube pins.

Generally when installing or removing octal tubes you should be grasping them by the base anyway.
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Old 30th December 2009, 06:51 PM   #6
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would potting compound work?
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Old 30th December 2009, 09:48 PM   #7
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Default Loose tube base

Thank you all for your input.
The RCA recipe is a most interesting but of historic trivia. Love it.
I'm thinking about the nail polish solution, but I will await further input.

By the way, I'm long past knowing not to use the glass to remove tubes.
These tubes arrived this way. Old Russian glue it seems.
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Old 30th December 2009, 10:30 PM   #8
SY is offline SY  United States
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Quote:
I believe the original glue that was used in this application was phenol-formaldehyde, or 'recorcinal' adhesive.
"Resorcinol," otherwise Dr. Polymer gives you an A+. Catalog number 7459A1 at McMaster-Carr.
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Old 30th December 2009, 10:42 PM   #9
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I've used clear fingernail polish on several small signal octal based tubes (6SL7GT, etc.) with good success. I've also used it on a couple larger tubes (6B4G, 6L6GC types, etc). So far, it seems to help hold the base tighter and no apparent ill effects to the tube.
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Old 31st December 2009, 01:08 AM   #10
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Default Loose tube bases

Thank you all for your input.
Got some good ideas.

jef
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