[R-390] SW R-390a Second Pass

[Ken Harpur]

Hi Jim,

I too have a SW and found exactly what you have...I've replaced nearly every mica in the radio...including the ones inside the RF tuned circuits. I replaced all resistors that were greater then 10% of their marked value. All paper caps replaced also.

End result is a radio that performs significantly better than before I started work. Particularly the RF deck...rebuilding that brought huge gains. The only downside is I used the 716P Sprague orange drops and no matter how nicely they are dressed, they just look ugly in there, moreso in the IF deck as there are so many in there...if only they made an axial version they would look more 'natural' in there.

I'm still not quite done yet. I am getting sensitivity variations between bands, not octaves but bands within an octave. The only module untouched so far is the Crystal Oscillator deck and I'm expecting a number of bad micas in there too causing the variations. So that will be investigated shortly...

Regards,
Ken
ZL3AA
 
On 15/02/2014, at 2:48 PM, N4BE_Jim <N4BE_Jim at Yahoo.com> wrote:

> I put my first 390a, a SW oldie, through its first refurb about 8 years ago.  I thought it was a hot Rx then.  After sitting more or less idle since then, it became once more deaf, compared to my 2nd radio, a Collins mfg 390a. So I launched into it again.  Discoveries:  I thought I had done a fairly comprehensive recap and resistor replacement in the SW back then.  But after further investigation with a capacitance meter, I now suspect just about every mica box and ceramic disc cap are out of tolerance or otherwise leaky. I was having to screw in too much inductance on the mixer and RF slugs.   So I am replacing all caps across IF and RF tuned circuits.  Already about 50% done, the performance is much better.  I will also be going inside the cans that have caps in them.  Likewise on the carbon comp resistors, drifted up out of tolerance.  Replaced every bloody resistor with new carbon films.  Almost like a new radio fresh off the assembly line now.  Lesson learned: I am over 
> the idea of wanting an unmodified museum piece.  Shotgun approach works.
> 
> Jim N4BE
> 
> Sent from my iPad
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