Glitch fuse for a pair of 3-500's

[KC4VWU]

Kanthal, like I use to build my vape coils with. Good for building meter shunts as well.

[K1JJ]

Kanthal, like I use to build my vape coils with. Good for building meter shunts as well.

Some good points...

What are the characteristics of Kanthal that would make it a good choice for a fuse?  And I wonder what material they use for standard fuses?  

I was also thinking about a thin piece of 60/40 solder that has a low melting temperature.

Jon, while you're in the testing mode, you might try a very thin piece of solder and see how it works.

Yes, nichrome wire is probably not a good choice since it would take forever to reach its melting point.  Probably a mushy knee.    I would think something like solder would have a desired fast avalanche property.

T

[w4bfs]

this has been an interesting topic ... look at what you are trying to do:

1. under normal conditions (current under I critical) conduct with as little V drop as possible

2. at I critical conduct and maybe glow as a warning - not really necessary - but continue to work at least briefly

3. abnormally high current draw - clear the circuit from the supply as nondestructively as possible generating as little byproduct as possible

It would seem to me that the third condition would call for a conductor that is as small in diameter as possible if the goal is to vaporize it as well as to melt it to minimize the unwanted metalic vapor or soft metal globules to keep out of the way .... if these are generated explosively then need some reasonable containment that can be readily changed with the fuse element

[W1AEX]

This has been an interesting thread and also a timely one for me. My AL-82 (pair of 3-500's running 3600 vdc) is an early one that pre-dates the glitch resistor update that is present in current production model AL-82/1200/1500 amplifiers. What Ameritron did was to install a 22 ohm 50 watt (or 35 watt depending on the vintage of the amp) cartridge type power resistor in the B+ lead close to where it is connected to the base of the RF plate choke. It snaps into big fuse clips that are mounted on the fiberglass baffle between the tubes and the lower chassis blower. I grabbed the parts direct from Ameritron to install this in mine to provide a little insurance given that I have some nice Chinese tubes in there. According to the designer, Tom W8JI, they went with a brute force approach and used a power resistor large enough that it would not fail before the primary fuses would blow. Time will tell but I guess it has protected those models fairly well when tubes or tank circuit components misbehave.

Rob W1AEX

[ka1tdq]

This is old, but I thought I'd report that it worked!  I'm not sure what happened, but mid-transmission I heard a "BANG!" and saw a bright flash.  My glitch fuse had disintegrated  and my homebrew plate choke had deformed some of the turns.  I was able to finish the QSO barefoot with 24 watts.  

So, I've had enough of high voltage stuff.  This amp has blown up on me twice and bit me once.  I just finished tearing it apart.  With kids around now, I can't in good conscience keep it around.  

I'm going all solid state and going to buy the Ameritron ALS-1300.  It won't have as much umph as a pair of 3-500's, but it will do 150 watts carrier with 150% positive peaks.

Jon