[Amps] L-7 Failure, HV fuses

[R.Measures]

>Re HV fuses:
>
>I have seen in the literature descriptions of a HV fuse made by inserting 
>into the B+ line,   a 30 guage Cu wire approx 2" long.  suspended between 
>two ceramic standoffs in the amp.  Would that function as a near 
>instantaneous HV fuse. protecting the tube in the event of a heavy current 
>HV fault?

**   2" of #30 Cu has about 0.017-ohms of R.   Since the ESR of 
high-ripple I 450V electrolytics is c. 0.25-ohms each, in a typical 
3200VDC anode supply, the peak discharge I would be 3200V / [(8 x 
0.25-ohms) + 0.017-ohms] = c. 1600A-peak.  IMO, this does not provide 
adequate protection.  As I see it, HV fusing is not needed if the primary 
of the HV transformer is fused or circuit-breakered.  What is needed is a 
device to limit peak discharge-I -- i.e., a sturdy-enough glitch-R;  
typical values of which are 10 to 30 ohms. 

cheers,  Pat 
>
>>From: "Jeffrey Madore" <K1LE at ARRL.NET>
>
>Said:
>Snip...
>(except in the case of "current limiting fuses" which open and
>>quench the arc very fast, but are quite expensive.)
>Snip:
>It would seem to me that a high voltage fuse located after the filter C, and
>>in series with an appropriate glitch R, would provide increased protection,
>>even more so if the filter C is large in capacity.   Is this reasonable /
>>practical?
>>
>>Jeff - K1LE - CT ><