Terry, see below in your text after ************

On Jul 7, 2:53 pm, terryS wrote:
Like your idea of leaving it 'as original as possible'. While having
it work for today using mains electric power. Good for you.

************** Thanks. We are only temporary custodians of "our
stuff".

Just a thought the original system worked off 28 volt aircraft
batteries. And of course the aircraft 28 v engine generators.
Batteries have a low impedance and might have done much to 'shunt'
brush noise of the various dynamotors?

************ True, but my 28 VDC supply is also very low impedance.

Could you try adding more shunt
filter to your 28 volt supply just to see if it could reduce the hash;
presumably coming back from the input brushes of the dynamotor?

************ I don't think that is happening
Or if
from brushes on the output side check hash filter caps there?

*********** Ditto.

Finally could you unplug the dynamotor and have a cable from external
PS plug into that socket? No other changes whatsoever! Retain
dynamotor (perhaps attached to PS?) for future re-installation.

*********** No, I can't risk the physical separation - the executors
of my estate won't go looking for the dynamotor! Neither do I want to
rewire the rear P/S socket - keep it original. My solution was to
installed a new 4 screw terminal plate (2 new small chassis holes...
sorry, can't help that!) with a captive power cord to the external
supplies. The dynamotor wires were just lifted carefully from the
original 5 terminal block to the new 4 terminal one (two are shorted
together in the original - see schematic. As we all now know for the
BC348, the external B- is NOT to chassis due to the odd biasing of the
6K6 o/p stage (it's about 14 VDC negative to chassis), so keep
external B- isolated!

Good luck with your project.

************* Thanks, keep 'em playing, cheers, Roger.

"Reclaim, repair, refurbish, rebuild, reuse, recycle"
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