[Boatanchors] Receiver Hummm --

[Howard Weeks]

Some years back, I spent a lot of time chasing a low level hum on an 
HQ-129 that I had just rebuilt.

Turns out that I was listening on a modern set of ear phones which 
respond down to about 30 cycles or so. The original speaker just didn't 
respond to any extent below about 200 or so cycles so you didn't hear 
what was down in the 60 cycle region.

Quit using the headphones - problem solved. Since that time, I have 
noticed the same problem on many receivers under the same headphone 
circumstances.

Howard K5JCP

On 3/4/2016 9:45 AM, GRANT YOUNGMAN wrote:
> I have two receivers which both exhibit the same hum issue to one degree or another.   I’m just not sure where to look.  One is a 51J-4, the other a Hammarlund PRO-310.  The J4 is the worse of the two.
>
> Normally, when not tuned to a carrier there is virtually no hum in the receiver audio.  Both radios have new good power supply caps.  The hum — which is 60 Hz — only appears when a carrier is tuned, and appears to be somewhat proportional to carrier strength.  So I’m guessing something around the detector/AVC or a bias (half wave) supply, although even with AVC off it still occurs. The source is before the audio gain control — so detector/AVC/ANL (?).
>
> Any suggestions where I should poke first?  I’m guessing this might be a fairly common problem, although I haven’t run into it before.
>
> Thanks … Grant NQ5T
>
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