[R-390] hum

[Natan Huffman]

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