[R-390] Need some R-390 info please

[Flowertime01 at wmconnect.com]

Phil,
 
Down load a PDF copy of TM 5820-357-35 for the R390 off the R390/A web pages.
A goggle search will find the TM for you.

The two MWO's were early changes to resistors and filter caps in the RF 
section of the R390 to prevent some parasitic problems. These MWO's have nothing to 
do with the other mods you are listing in your mail.

The R390 antenna relay assembly come in several parts. The R390/A antenna 
relay was reduced to one assembly. A part of the R390 antenna relay was a metal 
chassis made of about the same gauge metal as the other sub chassis and it had 
two relays mounted in the chassis. It is small about the same size as the 
R390/A relay. The parts from the two models will not swap. You need to do a real 
hack job on the R390 to get a R390/A relay into it. You may need to do this as 
R390 antenna relays are becoming near unobtainium.

I think Roy Morgans's idea of the diodes being used as a break-in keying is 
valid. 

I would be nice if you diagrammed the circuit and posted it where we could 
get a look at it. Some of the other R390 Fellows may want to try it.

Likely the original relay went bad. The connector was what was on hand to get 
the receiver going again.

The R390 has two antenna inputs. One is single ended and by passes the first 
set of RF selective transformers in the first stage of the RF section. [That 
first can with a slug and two caps at the front of the six RF slug racks] The 
other input was balanced and goes through the first set of slugs. Common 
practice is to ground one side of the balanced input and feed the other side with 
coax.

On the inside the R390 antenna relay had BNC connectors. You could couple one 
of the balanced inputs to the single ended relay input and feed the receiver 
with a coax. A shorting plug was then made up to either short the other 
balanced BNC inside the relay or at one of the pins on the twin ax back panel 
connector.

As these things are missing on your receiver, you need to find three coax 
cables going into the FR deck from the antenna input area. 

Depending on your antenna and listing needs you can then couple the antenna 
into the receiver as you need.

Good luck with the receiver and welcome to the group of R390 owners.

See Dave Medley's R390 page. Dave has been doing R390's since they were first 
let loose to the public. He has many R390 parts. He is getting old and does 
not read his mail daily. But if you need something, send him some mail and wait 
to see what he can offer you.

Roger L. Ruszkowski AI4NI


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