[Amps] One PS, many amps

["David G4FTC" <g4ftc@hotmail.com>]

Ian G/GM3SEK wrote:
> > The decoupling ?C? will provide the RF return paths for the input and 
> > output but provide the DC isolation.

> But only at the risk of RF instability in each amp.

Agreed - it would need some care in the layout etc. However having said that 
remember that the SB-220 series amps use a choke/capacitor combination 
between the grid and the chassis. That's a combination which I would have 
thought would have been a recipie for all manner of problems - but it 
somehow seems to work.

There must be some reasoning why Heathkit used that arangement but I'm 
afraid it's lost on me.


> I think it can be done by leaving each amp as-is, and adding a series diode 
> from each Ia meter to the common B-minus return. If you trace the current 
> paths, each amplifier's anode current returns via the cathode and its own 
> individual Ia meter. The diodes force each amp's grid current to flow in 
> its own tight local loop.

> It gets more complicated when you also add glitch protection diodes on the 
> B-minus rail and around the meters. Then the diode voltage drops have to be 
> counted much more carefully to make sure the circuits really do stay 
> isolated.

Sounds complicated. My arrangement is realtively simple and adding the 
glitch protection diodes shouldn't upset the isolation. Also the "Safety R" 
is a convenient detection point for PSU shut down in the event of an arc 
(assuming that the arc is from anode to grid). It would also be necessary to 
add a spark gap or similiar device across the "C" to both protect the "C" 
and provide a path for the arc current.

73s

David G4FTC


_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps