[Amps] HV Fuses

[Jim Thomson]

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From: "Fuqua, Bill L" <wlfuqu00 at uky.edu>

> Shorting the B+ to ground is exactly what a crowbar protector does!!!!!
> You discharge the supply allowing something else like a fuse that may 
> explode if need be
> to protect the tube.

## Ok, what his circuit described below is... is a cro-bar... and not a fuse 
!
All as this is going to do is  remove B+  from the tube [same as a HV fuse], 
then
create a new problem... a  solid B+  to chassis  dead short.   Now something
else has to handle the dead short... like breaker in the 240 line, etc. 
Unless
 a 2nd hv fuse is inserted between sec of xfmr.. and diode bridge, you will 
stress
the FWB.

## IMO, a HV  fuse would be simpler, and much faster. Glitch R limits the 
fault current,
hv fuse then interrupts the fault current.. and all in < 2 msecs.

##  BTW.. sson now has  5 kv hv fuse  [ same  13/16" ends, that fit a 3/4" 
clip],
in both 1.5A  and also 3 A. 
http://www.surplussales.com/Electrical/Fuses/ElecFuses-4.html

##  mating  3/4" fuse holders, with end retainers, [ so fuse can not migrate 
out] are here
http://www.surplussales.com/Electrical/Holders/ElecHold-1.html

## The  5" long  5 kv   [that's  5 kv AC / 7kv dc] rated  fuses, fit the 
above clips very tight,which
 is what u want.  With the  end stop retainer's, the fuse can be mounted 
Horz  or Vert.

##  silver plated clips  mounted to glazed ceramic stand offs.  In the 
interest of safety, I use
TWO  B+  meters.  One in RF deck,  [ effectively on output side of HV 
fuse].. and 2nd one
inside the  HV  supply itself,  wired between  INPUT of hv fuse.. and B-

## when HV fuse blows open... B+ meter in RF deck reads ZERO V.   B+ meter 
in  HV
supply STILL reads  full B+ voltage.   RF deck + HV supply are two separate 
box's,
and may or may not be in the same rack.



later.......... Jim  VE7RF

>
> Bill
>
>   I have thought a #30 wire or somewhat smaller wire was stretched inside 
> a grounded piece of copper
> pipe  such that there would be no discharge when HV was applied would be a 
> great fuse. This is because if
> an arc in the tube  would vaporize the wire and producing a plasma that 
> would short the B+ to
> ground via the surrounding copper tube or pipe.  Also, it would be easy to 
> replace.
>
> 73
> Bill wa4lav
>
>