Could be a bad cap, one installed wrong (it will blow eventually but it will
get real warm first), missing, miswired or bad equalizing resistor.
The transformer is trying to tell you to stop!
Carl
KM1H
----- Original Message -----
From: "Michael Tope" <W4EF@dellroy.com>
To: <amps@contesting.com>
Sent: Monday, February 15, 2010 12:41 PM
Subject: [Amps] L-4PS Transformer Buzz
>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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