[R-390] The R-390A project.

[David Olean]

I thought I was pretty much finished with my R-390A repairs.  I figured 
that I would install it in a relay rack next to my little 160 meter 
hamshack position. Imagine my surprise when I got the rack slides all 
installed and plopped the R-390A in and turned it on only to find that 
the carrier meter was non functional (AGAIN!). I had just repaired it by 
fixing a shorted bypass cap in the 4th IF amp cathode circuit.  I tried 
tracing wires and had the IF module out several times. It seemed the 
problem was intermittent. I even wired up a junk box meter inside the IF 
module and saw that it worked reasonably well.  After not finding any 
source of my trouble, I started to suspect the meter itself. I measured 
the resistance with a Fluke 77 DVM and saw 500 ohms! This is not good. I 
did some reading in the Pearls, and saw that a better number is about 17 
to 20 ohms. What is going on here?  It turns out that my sealed DeJur 
meter is intermittent and you can tap it a few times and the coil 
resistance drops to about 17 to 19 ohms. I am heart broken, but am 
hoping that possibly I can get some life out of it if it gets tapped in 
the correct spot!

I replaced a 15 MHz crystal for 12 and 27 MHz.  Larry H was kind enough 
to send me a slightly out of tol unit and it is working OK. (Thank you 
Larry!) After getting the unit all aligned, I find that the IF gain can 
be reduced to the lowest setting and the receiver works just great. Not 
all bands are identical, but they are close enough for gummint work. 
Sensitivity varies from 0.11 uv to about 0.15 uv. The highest band, 31.5 
MHz is at 0.11 uv for a 10 dB S/N ratio at 2 kHz bandwidth.

I am going to re do the alignment and use the balanced input connector. 
I am making a 50 to 100 ohm transformer with a little binocular core. I 
use 75 ohm beverage antennas for receiving antennas, so the transformer 
will be great. The initial alignment used the un balanced input.

I should take the DeJur meter out and see if it is really hermetically 
sealed. I'll bet the problem is an oxidized lug inside the housing.

Dave K1WHS