[R-390] hum

[Barry]

> I'm a very new subscriber and just received my first R390A today although 
> I
> became very familiar with this receiver during the 60's courtesy of Uncle
> Sam.  After checking tube seats I applied 120 VAC to the radio for the 
> first
> time today and was greeted by a nasty audible hum as soon as it was turned
> on and before the tubes had emission.  The hum is heard even with no 
> speaker
> attached and turning controls do not change the amplitude or frequency of
> the hum.  Tomorrow, I'll look at the output of the power supply board with
> my scope to verify any presence of ripple.
>
>
>
> Have I made an old beginner's mistake?  I do not remember this design 
> having
> a pronounced electro mechanical hum that is persistent after being turned
> on.  My R390A is a late model 1967/68 contract EAC model.
>
> Thank you,
>
> Natan W6XR

Natan,

Hmmm (no pun intended), I re-read your post.  If you're hearing 
electro-mechanical hum without the speaker, then it's probably not the 
filters.  These radios will hum just a bit like that, but it shouldn't be 
all that noticeable.  You could have a bad power supply transformer?

73,
Barry - N4BUQ