[Drake] Reply to two posts - power supply electrolytics and plate cap cement

[Barry L. Ornitz]

When using computer grade or other large electrolytic 
capacitors in power supplies, it is important to remember the 
vent plug.  If you use capacitors with screw terminals bolted 
to a printed circuit board or other insulator, it is important 
to drill holes so the vent plug is not covered.  If one of 
these capacitors ever shorts, the vent plug can usually 
prevent a dangerous explosion - IF IT HAS NOT BEEN BLOCKED.  
The bigger the capacitor (in capacitance), the more important 
the vent plug is.

On plate caps, I know of no source of the original cements.
I looked up the table of base and cap cements in my copy of 
"Materials and Processes of Electron Devices" by Max Knoll 
and found nine varieties.  Many of these are quite old 
"recipes" and would not be a good idea to use.  The more 
modern versions involved a Bakelite (Resol) varnish which 
produces the brown gunk you see in light bulb bases, a 
thermosetting phenol-formaldehyde resin [Dow Corning 2103], 
and a silicone resin [H. K. 15, Wacker Chemie].  These are 
rated for 160, 180 and 280 C respectively.  All three use 
anhydrous calcium carbonate as a filler material with the 
resin.

For small tubes such as receiving tubes and the sweep tubes in 
the Drake gear, the suggestion of JB Weld is not really that 
bad.  I have used the 24-hour epoxies here successfully.
Avoid the 1-hour types which are brittle.  I added some zinc 
oxide powder to the epoxy to let it better withstand the 
temperatures, but sadly you cannot buy this in drug stores 
these days except premixed with petroleum jelly and sold as 
diaper creme.  [Not everyone has access to the laboratory 
chemicals I used to, either.]  Powdered chalk should work as 
a substitute.  Use approximately equal amounts of resin, 
hardener, and chalk to make a very thick paste.  

Perhaps the most easily obtained cap adhesive for small tubes 
is a high temperature silicone rubber adhesive such as GE 
RTV-106.  You can probably find a more obtainable version in 
the auto parts store as Permatex (Loctite) Ultra-Copper high 
temperature gasket maker.  This is good up to 370 C in 
intermittent service.  I have used the GE version successfully 
many times. 

For high power transmitting tubes, I suggest Sauereisen 
Cement.  This is a high temperature ceramic cement commonly 
used in laboratories.  The Sauereisen company has a website 
and they do sell in small quantities - but a pound of the stuff 
would last the typical ham many lifetimes.

On octal base tubes, a loose base can often be corrected by 
flowing a drop or two of cyanoacrylate glue (super glue) 
between the glass and the base.  The high temperature silicone 
works well here too.  Use a finger to sparingly force a little 
between the tube and the phenolic base.

Naturally wash your hands well when working with these materials
and keep them away from your eyes.

        73,  Dr. Barry L. Ornitz     WA4VZQ     ornitz@tricon.net