[Amps] Large Zeners Follow-up.

[R.Measures]

On Aug 11, 2004, at 9:12 AM, ab5mm wrote:

> Thanks guys for all the help and recommendations.
>
> The overall best place to get 10 or 50 watt zener diodes was "Mouser 
> Electronics". They had them in stock and have no minimum.
>
> BTW, I used a string of fwd-biased Si rectifiers (thanks Rich) with no 
> problems except for space limitations and the fact that I had already 
> ordered the zener. I was actually able to fine tune the ZSAC a little 
> better with the rectifiers.
>
> In trying to get the amp back up and playing, I came across several 
> designs that place a 250Volt/.5 to 1 amp fuse in series with zener and 
> the center tap of the filament transformer. What do you guys think 
> about this? If it would truly act like a fuse and not affect other 
> things, it just might save a zener in the future.

Steve --  In order for the fuse to open, the tube would have to be 
conducting heavily -- i. e., there would be only a couple of hundred V 
across the tube.  If the PS was, say 2500v, subtracting a couple of 
hundred volts would leave more than 2kV across the 250v fuse as it 
opened.  - which will create a metal-vapor arc inside the fuse.  Since 
such an arc has a V-drop of c. 20v, there would be virtually no current 
limiting by the fuse until it exploded.  Meanwhile, a zener could 
short, or the tube's hot filament could short against the grid.
.  The bottom-line is when a fuse says 32v-max, or 250v-max, or 
1000v-max, using it in circuit with a higher potential is potentially 
trouble with a capital T.  .
cheerz
>
> Steve
> ab5mm
>