[R-390] R-390A balanced input question

[Craig Heaton]

Sorry Jim, we most likely took off on a tangent. So, do you have a sig-gen?
If so, connect it to the balanced input and trace the signal thru the
receiver with a scope. Swap the coax between the balanced & unbalanced, what
happens then? 

The balanced signal has to pass thru a couple more switch contacts, dirty? 

Craig,

-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of JAMES GREEN
Sent: Sunday, September 21, 2014 9:40 AM
To: r-390 at mailman.qth.net
Subject: [R-390] R-390A balanced input question

I have way too many projects to work on and just want to have a good
receiver to listen to when I'm not in the shop. I have an EAC R-390A that I
used to listen to quite regularly about a year ago. I put it aside for a few
months and started listening more to 2 channel Hi-Fi. I had the yen to catch
the BBC out of ascension Island again so I pulled it out and ran into a
small problem.

Knew exactly where the radio was stored. I can't for the life of me find the
"C" to so-239 adapter I used before to hook it to my antenna. I did find a
balanced to SO-239 adapter, but I found I could not get a signal from the
balanced input. Upon close inspection and some dis-assembly I found the
plastic insert in the balanced connector was twisted. This twisted the relay
contacts so there was no connection. I replaced the antenna relay with one
from my parts radio & have verified it is now passing a signal. 

Here is the problem:

I still am unable to pick up anything through the balanced input. Upon
looking in the R-390A Y2K manual schematics it looks like the unbalanced
connector bypasses several tuned transformers that the unbalanced input does
not bypass. I suspect these tuned transformers are in need of alignment.
However, the alignment procedure in the Y2K manual instructs one to connect
the sig gen to the unbalanced connector. & aligning from there.

Am I missing something? Is there a separate alignment procedure that I did
not find that shows how to align from the balanced input?

Cash flow at the moment prevents buying another "C" to SO-239 adapter, & I
have heard some extra sensitivity can be gained by using the balanced input.


Jim
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