I had a good number of replies to my questions concerning likely output for
the Alpha 78 and in the process uncovered what is clearly a problem here
with the AC supply line. The distribution is done from the breaker panel to
the wall outlet with 2.5mm. Breaker panel to main breaker is 35mm and the
feed from the street is in what looks like the next size up from that.
Measured about 10 volts sag in the AC line at the wall outlet with the amp
key down 1.5K out. Sag drops to 2.5 volts when I use 6mm cable Also measured
about 90 volts AC sag on the secondary of the transformer in the SSB
position. Seeing approximately 350 volts sag at the output of the power
supply filter. Why so much?
Measured the ripple by looking at the voltage across the 180K HV metering
resistor. Saw approx 8 volts pk-pk off load rising to approx 25 volts pk-pk
at full output. Added a bank of 6x470uF capacitors and the ripple reduced to
approx 6 volts off load and neglible on load, can see the 20 metre RF
getting in the scope but that's all. DC still sags down 350 volts on load.
Changed the diodes out replacing the RCC1733 with a string of 3x1N5408's in
each case, no difference, DC still sags 350 volts.
If this is about right can anyone explain why? Others have indicated to me
that they see approximately 200 volts of drop between no and full load.
Think I could maybe accept that but not yet cofortable with 350 volts drop,
Any ideas?
Just as a thought , not that it would make that much difference but I really
couldn't say. Electrical supply here is 50Hz not 60Hz, would that be enough
to render the transformer a Peter Dahl 2.4KVA Hypersil meant for 60 Hz, a
little on the wimpy side?
73
Martin
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