[Amps] One PS, many amps

[David G4FTC]

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