[R-390] hum

[odyslim at comcast.net]

Get a screwdriver and put the tip on the power supply case put your
ear on the plastic end. It would not hurt to insulate the tip of the
screwdriver.
 Do you hear the hum? It could be the casing
of the transformer. EAC transformers are very noisy. 

  

Regards, Scott

----- Original Message -----
From: Barry <n4buq at knology.net>
To: Natan Huffman <w6xr at frontiernet.net>, r-390 at mailman.qth.net
Sent: Sat, 25 Jul 2009 03:49:38 +0000 (UTC)
Subject: Re: [R-390] hum

> 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 

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