[Amps] grid fuses

[Lon W. Cottingham]

Greetings to all,

            This discussion has deteriorated  to that of electing officers 
at a 7th grade 4H Club Meeting.  The original point has long been forgotten. 
Who cares what you call it; grid protection or grid fusing.  The results is 
what we should be after, not all this, mostly unrelated, speculation and 
theory.

            One thread that I have taken from this bilious discussion is 
that some of you do not realize that most of the commercially built Amateur 
triode linear amplifiers throughout the 70's, 80's, and 90's have floating 
grids, of one sort, or another.  It is time to pull the heads out of the 
sand and realize this.

             More often than not, when the "big bang" occurs, the tube/s are 
lost/shorted.  Anyone who has been repairing amps and uses "grid fusing" 
knows that the loss of tubes is reduced by approximately 50% with grid 
fusing when the "big bang" occurs (at least that has been my findings over 
the past 25 to 30 years repairing 3 or 4 linears each and every month.  I do 
not care why it works or what you call it, it works.  In my opinion, grid 
protection, of some sort, should be a standard upgrade, along with anode 
surge resistors, in any amplifier repair or restoration.  Inexpensive 1/4 or 
1/2 watt resistors are the most cost effective way to do this that I have 
found.  This idea of using anode surge suppressing resistors alone, as has 
been suggested by some of us,  to protect the tube/s is like starting to 
brush your teeth after they all have cavities.

         I would like to see a thread start on trying to salvage shorted 
tubes.  My success ratio over the years has been about 1 in five.  Richard 
has mentioned a technique of spinning the shorted tube at a high speed in 
some sort of a centrifuge.  I have heard other techniques such as  applying 
voltage (both AC and DC) across the short.  Some have suggested discharging 
large capacitors across the short.  One Ham I know simply attaches an AC 
line cord across the elements and plugs it into the mains.  Apparently this 
works, some times.  I have always wanted to try Richard's method but simply 
have not done it.  I would like to hear success rates from the various 
methods.

73 de K5JV

 Lon W. Cottingham
1110 Golden Bear Ln.
Kingwood, TX 77339

281-358-4207
281-358-4234 FAX
281-795-1335 CELL