[Amps] Question about separate power supply/RF section amp

TexasRF at aol.com TexasRF at aol.com
Thu Jan 17 20:59:33 EST 2013

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.
Gerald K5GW
In a message dated 1/17/2013 3:35:11 P.M. Central Standard Time,  
k2vco.vic at 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  

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?

Vic, K2VCO
Fresno  CA

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