Hi Vic, as you say, installing another diode inside the amplifier can't
hurt so why not?
The only downside that comes to mind is that the added diode could be the
one that fails due to an arc and might be more work to replace than one in
the separate power supply.
You no doubt have included a B+ surge resistor in the amplifier or the
power supply to limit fault current. With a well chosen primary fuse size one
would hope the diodes would be protected from an over current failure.
73,
Gerald K5GW
In a message dated 1/17/2013 3:35:11 P.M. Central Standard Time,
k2vco.vic@gmail.com writes:
I'm building an amplifier with a separate power supply. The PS is a unit
that sits on the
floor. I wanted a small desktop amp and there's no room for a rack.
In the power supply section, I have a 0.33 ohm 5W resistor in parallel
with a 6A10 diode
between the negative output of the power supply and the chassis. The idea
is that there
will be 0.5 V across the resistor when the full 1.5 A is drawn from the
supply, which will
be read by the plate meter. The diode conducts at about 0.68 V, so it
won't interfere with
normal currents, but will protect the meter if the current goes much
higher.
Now here is my question: suppose there is an arc to ground in the RF
section. It will
instantaneously raise the chassis of the amplifier to a high potential
relative to other
grounded things. The interconnection between the power supply and the RF
section includes
a no. 16 ground wire, the braid of the RG59/U HV lead, and a no. 16 B-
lead. The length of
the cable is 10 feet. The arc current will have to flow through all of
this plus
connectors in order to flow through the diode back to the negative side of
the supply.
Is this a safe arrangement? I am thinking of adding another diode from B-
to chassis in
the RF section. I don't see how this could hurt, but it might help clamp
the voltage in
the event of an arc.
Any comments?