The Alpha 87a shouldn’t even have a neutral as there isn’t one on the line
cord. The line cord should only have two hots and a ground. The supply from
the receptacle should only have two hots and a ground. The ground is connected
to the chassis. The two hot legs are generally bypassed to ground with bypass
caps inside the amp. It could be that one of them is leaky as they are always
hot with AC.
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On Monday, May 3, 2021, 1:26 PM, w5cul@sbcglobal.net <w5cul@sbcglobal.net>
wrote:
Good Afternoon Gentlemen,
I have a rather quirky situation and a question about it. I have been
chasing down a low level 60Hz hum I get across my speakers when I plug my
Alpha 87A into a shared A/C Service for the shack. I say shared because I
am referring to a dedicated 6AWG 220Vac line that runs from the Main
Electrical Panel for the house to the shack (bedroom). From there it is
connected to a Sub-Panel that splits out 2ea 220Vac Lines and 2ea 120Vac
Lines all with appropriate CBs. All the 120Vac equipment to include
Transceivers, computers, speakers etc...are powered by the two 120Vac lines.
The Alpha is powered by one of the 220Vac Lines. So as the issue goes, with
all the 120Vac plugged in and powered up, transceiver turned on, white noise
emanating from the speakers, the moment I plug the Alpha 87A into one of the
220Vac sockets, CB turned off, I immediately get a low level 60Hz hum coming
out of the speakers. Since this sounds like a neutral or ground feedback
loop, it prompted me to check the wiring on the Alpha. So I unplug the
Alpha and perform a continuity check from Leg 1 of the plug to the chassis
of the Alpha, Leg 2 to the Chassis and Neutral to the Chassis. As for the
120Vac Legs, there is no continuity to the Alpha Chassis. But there is
direct continuity from the Neutral of the 220Vac Alpha plug to the Chassis
of the Alpha. So the question I have is should the Neutral on the Alpha
plug have such continuity to Chassis Ground, or do I have a bad Capacitor
somewhere in the Alpha? I will say that the Alpha 87A does operate as it
should and does put out full power.
Thank you in advance,
Mike
W5CUL
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