Dale is obviously an experienced "old school" Ham who no doubt has rewound a few transformers - something we used to do a lot of in the 50's but I suspect is almost a lost art in "Hamdom" today.
If the windings are loose, his suggestion is excellent. It will also extend the life of the transformer since those vibrating windings will eventually wear through the tough insulation on them and short. But, you said the hum goes away when you press on the top cover of the Astron. That sounds like it is being vibrated by the magnetic field around the transformer, rather than coming from inside the transformer. Most such power supplies have an audible hum when close by for just that reason. Are all the screws on the Astron tight, including the mounting screws for the transformer, etc? I've "tamed" few by tightening the fasteners, but never completely silenced them. In general, I never put a power supply on the operating table. The magnetic field can wreak havoc with sundry electronics - the distance depending upon the sensitivity. My Astron powering a K3 is on a box under the table where I am unaware of any hum, but it's quite evident in a quiet room if I set the supply on top of the table. If it must be on top of the desk, and the supply is quiet when you take the cover off (so you know it's the cover and not the transformer vibrating), consider adding some dampening material to the cover, either on the outside or the inside. (Consider storing the latest ARRL Handbook on top since pressing there silences it, Hi!) Rubber padding, carpet, etc., all make good vibration dampeners, but they must be attached to the metal to transfer the energy to the dampener. Also, keep it away from a corner. Corners are excellent sound amplifier/directors that can have a huge impact on the sound level. Even a hard, flat surface nearby can add several dB to the sound level. Ron AC7AC -----Original Message----- I've not repaired a high current xfrmr, like that one, but have the lower current ones... With hum that is physical, and a vibration, that maybe caused by the varnish breaking its hold and letting the individual windings rattle. I may have just been lucky too... all I did was take the transformer shells off, exposed windings are now very visible, although only the top winding... and a cheap wager would be that it isn't the top one rattling... then very slowly pour new vanish onto the windings. Let it settle some, and add more.. yep,.. it is messy... very messy.. not something you'd want to do on carpet... or cement... or in a sink... trust me here... and that is another story.. really. Let it settle in,.. add more.. when it seems to not want to do anywhere, but on your shoes... maybe now would be a good time to stop. Let in air dry... for a long...long ... long.. time. well... ok.. tomorrow then. (24 hours.... it is always tomorrow somewhere) Put it all together... and hum.. away... well.. hopefully at least, it is away. Have a great day, --... ...-- Dale - WC7S in Wy > > >I have an Astron RS70M linear supply that I've used for many years to > > power everything 12VDC in the shack, including my K3. In my former QTH, > > I had it located under the operating desk and never heard a peep from it. > > > > In my new shack, which is considerably smaller, I hear an annoying hum > > from it which seems to be coming from the top of the case. It goes away > > if I press down on it. Any ideas how to get rid of the noise? > > Tnx, > > Barry W2UP > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
