[R-390] R-390A help

[Cecil Acuff]

Hi Tom,

        Congrats on the R-390A.  You'll enjoy the project.  Sounds like the 
fuse holder problem is easily fixed and pretty obvious as to how to do it. 
If I remember correctly one of the fuse holders never had anything connected 
to one lead...I am working from memory here but I think it is the one marked 
20 amp....I'll have to go look.

Pull the power supply out and look under the bottom side of the tube 
sockets...I am guessing you'll find solid state rectifiers soldered onto the 
tube socket pins.  That was a military mod.  Crushing the tube socket bases 
was to ensure tubes were not placed in the sockets after the mod was done. 
It's no big deal.  You will find differences of opinion on the list as to 
the suitability of the mod but personally it works fine.  The selenium 
rectifier is factory...it supplies a couple of things.  The break-in relay 
and the antenna relay.  If it's not causing the relay to buzz or chatter 
it's ok for now.  I usually replace them with a silicon bridge just to 
improve long term reliability...they are quite nasty if they fail and spew 
their guts!

The top and bottom covers are available as reproductions or Fair Radio may 
have some.  The reproductions are sold on ebay quite regularly...

Hope that helps...

Cecil...


----- Original Message ----- 
From: "TChirhart" <sparks at codepoets.com>
To: <r-390 at mailman.qth.net>
Sent: Friday, March 17, 2006 9:00 PM
Subject: [R-390] R-390A help


This is my first R-390A project. I have an Imperial 1963 vintage R-390A
and the previous owner may have modified it. First of all, all 3 fuse
holders are either missing or have been bypassed, the AC, B+ 1/8 amp and
B+ ¼ amp have been bypassed with F-102 B+ ¼ amp fuse holder missing..

F-102 B+ ¼ amp fuse socket, near power supply is missing and two wires
soldered together.
F-101 AC 3 amp fuse has been bypassed, fuse socket broken
F-103 B+ 1/8 amp, fuse bypassed inside.

In the power supply, the 2x 26Z5's are missing, the metal tube sockets
crimped and a selenium rectifier installed over the sockets and the
F-102 fuse holder is missing, apparently this is a modification.
But why would you bypass the AC and 1/8 amp B+ fuse?

Am I missing something here?

It makes no sense to bypass all 3 fuses, especially the AC fuse socket.
The fuse holders are damaged, but can easily be replaced. I would hope
that the previous owner had enough sense to replace a simple fuse
holder...but...

I've pulled out all the tubes and found over half of them bad or very
weak.

This is my first time going into an R-390A so I'll need some advice from
you experts.

Also does anyone have the top and bottom covers for an R-390A?
Thanks in advance
73
Tom K4NCG



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