[Hallicrafters] SX 101A hum

[Kenneth G. Gordon]

On 5 Feb 2008 at 13:18, Roy Morgan wrote:

> 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.

Yes.

> 
> 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.

The HQ-129 often has a lot of hum, most of which is 
reduced, and sometimes eliminated by unbolting the power 
supply choke, and/or the audio transformer and rotating it 
until the hum level goes away, or drops to a minimum level.

Go, Thou, and do likewise.

Ken Gordon W7EKB