I just installed the Harbach PM-400 in the L-4PS power supply for one of
my Drake L-7 amps after I popped a rectifier diode in the old bridge:
http://www.harbachelectronics.com/main/page_products_drake_l4l4bl7.html
Electrically, the amp and power supply appear to work perfectly with the
Harbach board. Plate voltage and RF output are as expected. There is one
problem, however. Last night about 20 minutes after I fired up the power
supply I noticed a loud 60 Hz buzz coming from the supply. Pressing on
the sides of the cabinet or changing the physical orientation of the
supply didn't seem to help. When I switch to the low-voltage setting on
the L-7, the buzz stops. Also if I let the supply cool off the buzz
stops for a while and then returns after the supply warms up. Looking at
the supply in the dark, I saw no evidence of sparking. Additionally, the
amplitude of the buzz seems to be totally unaffected when I go from
standby to full RF output power.
Any ideas on what might be causing this problem?
Thanks,
Mike W4EF......................
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