[R-390] R-390A help

[Barry Hauser]

Cecil wrote:
> 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.

20 amp?  That's the DC fuse on the R-390/R-391, not on the R-390A.  Probably 
not used on stock R-390's, but is used for the 28 vdc external supply for 
the autotune on the R-391, thus probably not connected in the R-390. (also 
might have been for some other 28 vdc equipment on the R-390, or for an 
alternate dynamotor supply -- but those have "@RARE@" encrypted into the 
contract number.

All three fuses should be wired in to properly protect an R-390A.  You're 
right Tom -- it makes no sense to bypass them, unless you feel lucky, very 
lucky. ;-)

>
> 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!

I dunno, sounds like Tom was possibly referring to an _added_ selenium 
rectifier.  If the previous owner jumpered out all the fuses (wore a 
sombrero and said at the time "wheee don' need no steeenkin' fuses. Hah Hah 
Hah Hah Hah.  But wheee do need another maybe steeeking selinium 
rectifiers!")  Could have felt fuses were superfluous but seleniums were the 
best thing since sliced bread -- and look something like a bread slicer. 
Probably not, but ya' never know.  "Radio Bart does it again!  Rare fuseless 
double-selenium Collins designed, almost-Mish-Rippel-like R-390A.  So 
reliable was this model with it's rare Cosmos PTO and special, high 
reliability hermetically sealed molded capacitors, drift-proof carbon comp 
resistors, and mercury-laced MFP coating -- it didn't need the protection of 
common glass fuses ..."

(Am I getting the hang of that?  Sometimes I scare myself.)

My 2 cents woith.
Barry


>
> ----- 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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