[R-390] Re: little things

[W. Li]

Over the years, I have made some little additions to
my trio of R-390A's that may be of use to you guys.
Most are obvious and simple (about my speed nowadays).
Most are not original with me, but have been mentioned
in earlier posts through the years. 

Antenna input
I used Chuck Rippel's suggestions for the balanced
input. What I did was house his circuitry into a small
aluminum box that bolts onto two existing rear panel
screws. Has both a SO-239 and a BNC socket with a
0.01uf blocking cap. Makes a neat and tidy
installation. An Asante coax transceiver case is about
the right size.

F101 and old two conductor pwr cord
Got rid of both, and filed the rear circular opening a
bit to accept a new Corcom EMI power receptacle...
grounding it to the chassis, and hooking up the hot
lead to the fuse F101. You do have to drill two small
holes in the rear panel to secure the Corcom. Any
computer grade power cord may now be used.

TB-103
Jumpered 6 and 8 to bypass R101 (6800 ohm) to increase
output. Works.

I-177 5814A accessory
Those of us with I-177 tube testers know that you can
not check 9 pin miniature tubes without the MX-949U
accessory. Of course, you can make up your own with
all the jacks and leads...but all I wanted today was
to check 5814A's, so I made up a simple plug-in for
socket E using the octal male plug with its metal
mounting plate scrounged from a surplus octal relay
case, a Bud minibox with a standard 9-pin tube socket
at the other end, and a 6-pole-two-position
non-shorting wafer to switch the plate-grid-cathode
leads between the two triode sections... all built out
of junk-box parts in an hour. Works swell to rapidly
screen through those one dollar hamfest 5814A's before
I actually test them in a receiver. Parenthetically
though, I think that tubes are best evaluated in a
real circuit.

C603 and C-606
To reform these capacitors I used Roy's circuit, but
rather than have everything exposed and take the
chance of getting zapped: i dived into my junk box and
rescued a 2.5A Variac, TV pwr transformer, 0-500v
voltmeter and multirange-milliammeter, and a 1A fuse.
Stuck it all into a enclosed case that's grounded and
painted it Navy grey. A 3PDT toggle either powers the
Variac up or discharges the electrolytic thru a 1000
ohm bleeder. I have a lot of larger BA electrolytics,
so this little project saved a lot of 'haywires'. Two
General Instruments and one Pyramid electrolytic
falied, but the Sangamo's & Cornell-Dubliers reformed
nicely with only 0.3mA leakage at 250v.

Audio deck
Nolan had an idea to mount four washers as a
"mini-stand-off" under this subchassis to allow some
heat to leak out when it is mounted into the frame.
This may or may not make thermal sense, but it doesn't
hurt.

220VAC muffin fans running at 110 
One of these days I plan to mount these fans outside
the sides to blow air into the frame over the AF deck
and out the top. They sold for next to nothing at
Radar Electronics in Seattle.

W. Li
Mercer Island, WA


		
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