[AMRadio] R-390A Help


w3slk at verizon.net w3slk at verizon.net
Mon Jul 7 18:59:35 EDT 2014


Bill,
    I'm not much of a 390A guy but I have worked on mine. First thing would 
be to check the input line filter. It is a small square little metal box 
type set up that is fastened to the upper rear bulkhead of the receiver. I 
had mine go out and I just removed it. The Navy used tons of the R-390A's 
because they were impervious to interference from shipboard radars. Thus the 
reason for the filter. You don't need it unless your antenna systems is so 
unbalanced you are getting into your powerline.

Mod-U-Lator,
Mike(y)
W3SLK

-----Original Message----- 
From: Bill Guyger via AMRadio
Sent: Monday, July 7, 2014 6:45 PM
To: Discussion of AM Radio in the Amateur Service
Subject: [AMRadio] R-390A Help

Hi All

I acquired a 390A over the weekend from a friend who can no longer see to 
work on his gear. He made me promise to not sell it or trade it while he was 
still alive which I wouldn't do anyway out of respect to a genuine 
gentleman, a fine ham and one hell of a builder of radio related gear. 
Returning it to the air is my way of honoring a long time friend.

The last time he fired it up the line fuse blew preceded by a sound like one 
might experience after too much Mexican food and a wisp of smoke. He 
suggested something in the power supply which seems pretty basic other than 
Collins' use of 26Z5's for rectifiers. There's not much else there except 
for chokes and a couple of caps which date from the 1960's.

I haven't had time to really dig into the unit, and those old caps seem a 
logical place to start in addition to suspecting one of the rectifiers. 
Hopefully lightning etc. didn't get into the radio and fry something when he 
wasn't looking.

My question to some of you R-390 gurus out there is. Is there a history of 
Power Supply issues and does anyone know of a source of 26Z5's. Or....if 
it's not heresy could I replace them with Silicon rectifiers after doing 
something about the additional B+ that will create? Not sure I want to 
pillage a great radio by doing that anyway if I can find the correct tubes 
but it's a consideration.

Many thanks and 73 Bill AD5OL
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