> Once, somewhere, I read that the surge limiting resistor should be of a
> value
> that will drop at least 25% of the plate voltage at 5 times the normal "max"
> current of the supply. And, the wattage rating should be exceeded by a
> factor of 10 or more at that current (so it will fail as needed - like a
You are painting with too broad a brush.
It depends upon several factors.
Eimac and others specify the maximum joules allowed for each
specific tube model, so that is the starting point in "doing the math."
This will vary depending on your choice of tube(s).
The glitch resistor must be robust enough so that it will not fail during
the time it takes for the mains circuit breakers/fuses to trip during a
glitch.
> with special HV fuses (also expensive and hard to find).
HV fuses are too slow for use with a capacitor input HV supply.
>
> Would the "dale" type power resistors that bolt to a chassis work better or
> worse?
Worse...the Dale resistors will arc from the post to the case, even if mounted
on an insulated block. I have experienced terrible results with Dale units when
trying to use them in a bleeder string.
> What are the pros and cons of each type? It seems the "dale" bolt-down
> would
> tend to minimize 'shrapnel' in the power supply (if it blows) due to its
> basic design.
Never use the rough "sandpaper"" type resistors. The Ohmite type slick
brown finish units will usually fail by breaking cleanly in two pieces.
>
> What are the "rules of thumb" with regards to joules (watt-seconds) ratings
> in such
> a case? My present project application will produce 5000 VDC at 1.0 amp,
> and I want to be such the tube is protected. I am currently considering 50
> ohms
> at 100 watts.
The spec sheet on your tube in question will tell you the maximum joules
allowed. Some even specify the glitch resistor value to accomplish this.
Good luck, Jim!
(((73)))
Phil, K5PC
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