PDP-8/A transformer hum

[Josh Dersch]

Hi all --

I'm working on a PDP-8/A I picked up at VCF West last summer.  After a lot
of cleaning and some power supply repair it's showing signs of life (CPU
seems to be at least minimally functional, core memory is going to need
some debugging.)

The transformer in the power supply is humming quite loudly, however, and
I'm curious if this is normal for the 8/A (or is typical for an 8/A of this
vintage).  I'm used to the supplies in various other DEC machines not being
exactly silent but this is a rather severe 60Hz buzz that you can clearly
hear over the fans when the machine is in operation.

Thanks,
Josh