[Amps] PSU design question

[Bill, W6WRT]

ORIGINAL MESSAGE:

On Sat, 7 Nov 2009 17:28:31 +0100, Ulf Tjerneld <star at frizon.org> wrote:

> He explains that they  
>serve a a return path to ground for surge currents and that the 100  
>ohm resistor is there to act as a backup for the diodes. But he does  
>not mention anything about how the metering is accomplished in this  
>case; with a 100 ohm you would have maybe 25-35 volts over the  
>resistor, so a meter would have to be shunted. And when shunted we  
>would bring down the resistance to a low value again which in its turn  
>would make it unnecessary with such a high value in the first place.  
>At least according to my logic!

REPLY:

Your logic is correct. To have a 100 ohm "backup" for three large diodes is
silly. In my 50+ years of electronics I have never seen a silicon diode fail in
the open circuit mode. Invariably when they fail, they develop a dead short. To
have three fail open, well...... you would have a better chance of winning the
lottery ten times in a row.

That 100 ohm resistor will be the loneliest part in the whole amp.,  :-)

73, Bill W6WRT