[Hallicrafters] SX 101A hum

[Roy Morgan]

At 10:18 AM 2/5/2008, Andy Bullington wrote:
>...my SX 101A.... on using headphones I'm noticing an annoying hum.... 
>Using a speaker the hum isn't as noticeable but still there. ... I get hum 
>even in standby or with the audio turned all the way down or the audio 
>tubes removed. It's not run you out of the room hum, but it shouldn't be 
>there. Is it something in the power supply? Thanks in advance.


Andy,

Yes, with the tubes (audio preamp and output tubes) removed, hum in the 
earphones is likely caused by induction from the power transformer to the 
output transformer.

Get a chunk of steel plate and move it around the radio (tubes out, 
listening with phones) between the output transformer and other things. You 
may find a place that at least affects the hum if not reduces it a lot.

Another thing is to unbolt (or un-rivet) the output transformer and rotate 
it if possible.  That may help.  Some audio hifi amps have the output 
transformers mounted at odd angles to reduce hum.

Roy





- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing
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