26-11-2012, 10:23 AM
(26-11-2012, 09:47 AM)Yorkie Wrote: My understanding of modulation hum (if it arises) is that it is caused by the mains lead to your set acting as an 'aerial’, picking up some RF energy in strong signal areas, which is modulated by the 50Hz mains frequency. (In DAC90As, any hum is most likely caused by the UL41, though I dare say a lot of restorers have needlessly replaced the twin electrolytics suspecting them as the culprit. In or out, the mains suppressor in DAC90As seems to make not one jot of difference in my experience).
Hello David, yes, I get that on some of my receivers where I have chopped out the mains filter capacitors and not got round to replacing them.
At my location it is worse on MW broadcasts ie: no interstation hum but hum when tuned into the station, I have also noticed that it is worse when using a receiver that's running off my Variac when the receiver in question is a 115 volt input receiver, might be compounded due to the output impedance of the Variac, it is always worst at night time here.
Lawrence.
