David G4FTC wrote:
>Iâm wondering if for triode amps the solution may be simply to
>isolate the DC path from the grid to the chassis of each amp so as to
>prevent one amp affecting the meter readings of another amp.
>
>See my sketch at http://www.qsl.net/g4ftc/amplifiers/multiamp/multiamp.jpg
>
>The decoupling âCâ 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.
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.
>My concern in using a single PSU in a multi-multi contest station would
>be that should a glitch occur in one amp, then the protection circuit
>in shutting down the PSU would effectively take the whole station off
>the air.
>
With reliable amps, that won't be a practical problem... it doesn't seem
to have affected W3LPL's contest scores too badly :-)
However, if each amp controller has the "right" to shut down the B+
supply, it could be an interesting problem to get all six amps started!
--
73 from Ian G/GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
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