[Hammarlund] vibrating hum on sp600?

[Eugene Hertz]

Hello all,

Just received my GenRad 1001A rf generator and have been starting to learn about how radios work and how to use test equipment with them.  Had a question.

When I turn on my sp600 with the rf and af gain set to "0" I can hear an audible hum coming from either the big transformer or the shorter one right next to it, I am not sure. It is 60Hz, but appears to be a mechanically produced sound vs from a speaker or any audio chain.  Kinda like if you walk by some of the very very large transformers used in power distribution, even tho there are no speakers you can hear these transformers "buzz"  In my case, the sound is very low, but somehow annoys me!  Question is, is this normal? Is this portending some disaster with a transformer? Could additional caps help this? The audio of the radio is very quite with no hum whatsoever.