[Amps] Surge resistor

[rgroh at swbell.net]

Lost the original contents of your message but I think this might be some information of value regarding the surge resistor.

I took a quick look at Eimac's 'Care and Feeding of Power Tubes' application note (available on their site in a pdf file, by the way) and, on pages 67 to 70, they talk about the subject of protection against arcing. One of the recommendations is the use of a large resistor (10 to 50 ohms) in series with a FUSE (my emphasis) in the anode power supply.

So you are quite correct in your analysis - the 0.5 ohm resistor is being used as a fuse. 

One point -  You have to be careful in using physically small items as HV fuses - leave enough physical distance from end to end so that arcing will not sustain itself. Also mount the 'fuse' away from ground and away from anything that might catch fire when the 'fuse' lets go

Eimac indicates the large resistor can be a bulk-carbon or a wire wound device.

Lots of other info in the Eimac application note - I suggest you download a copy (you can Google for it) and save it for future reference - six separate files ranging from 350 kB to 900 kB. 

Hope this helps.

73
Bob, WA2CKY