Astron 35 a Humming

Astron 35 a Humming

Is there any cure for the audible humming noise coming from an Astron 35 power supply. I vaguely remember an article about people tightening down the transformer to the chassis to solve this problem, though, I could be wrong.

loose laminations in a standard EI core analog transformer are fairly common, and cause hum and vibration. tightening down the bolts as they pass through the shells and laminations frequently provides relief. occasionally the bobbin full of wire shakes loose of the core, and might need a wedge to keep it from vibrating. and while you're fooling around there, tighten the transformer to cabinet fasteners.
if that doesn't do it, at least try to get it to hum in your own key, so you can sing along for the 40 to 50 years it will take for this to damage the transformer so you can replace it.

http://www.eham.net/ehamforum/smf/index.php?action=printpage;topic=88978.0

http://forums.qrz.com/archive/index.php/t-57472.html

http://www.repeater-builder.com/astron/astron-intro-stuff.html


Often, the mechanical noise you hear from the Astrons is coming from the thin sheet metal cabinet.  When you're hearing the hum, put your hand on the cabinet top and press down lightly.  If the noise is substantially changed or reduced, the problem is that the steel cabinet is being affected by stray flux from the transformer.  One way to fix this is to damp the cabinet - something you'd normally do from the inside, but there's no room in the Astron to do that and the cabinet top can't be simply pulled straight up anyway.  The way it slides would prevent using damping material inside.  You could apply damping foam (adhesive backed) to the top of the cabinet on the outside and that would help a bit.  The foam can be obtained from a number of companies on the web who deal with quieting down noisy PCs.  

Another approach might be to take the steel cabinet top to a sheetmetal shop and have them bend an aluminum top for you.  I've had more noise problems with Astrons from this source than from loose transformer laminations or bolts.

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