[ARC5] nasty hum

[Kenneth G. Gordon]

On 25 May 2015 at 20:54, J Mcvey via ARC5 wrote:

> I just recapped a BC453 beacon receiver ( with NOS late issue plastic top "pot
> caps", which test OK-ceramic?) . It works pretty well even before alignment, in
> fact it's a little better than my Yaesu FT450 on that band. I'm using a well
> worn 28V dynamotor, runnin on a clean 24V supply.When I turn the gain down
> enough to where there is no receiver audio, the background hum becomes
> obvious.Its a positive almost triangular looking glitch on the scope. 
> 
> Is it the dynamotor or are my NOS caps not so NOS?

Probably the dynamotor. Make sure the dynamotor itself is grounded to the 
receiver. ARC used two thin copper "straps" at opposite corners of the 
dynamotor mounting which connected the frame of the dynamotor directly to 
ground.

The wire in the bottom of the dynamotor plug which connects the minus side 
to ground is not enough. The frame or case of the dynamotor must be 
grounded.

Ken W7EKB