[R-390] Did the LF Mod today. . .

[Bill Smith]

What preamp circuit do you use?

73 de Bill, AB6MT
billsmith@ispwest.com


----- Original Message -----
From: Phil Atchley
To: r-390@mailman.qth.net
Sent: Tuesday, July 22, 2003 7:22 PM
Subject: [R-390] Did the LF Mod today. . .


Hi All.
Today I finally got around to doing the LF mod to my R-390A.  Now before any
of you scream bloody murder, holler "Blasphemy" etc let me hasten to add
that this is a simple no holes drilled no soldering to the radio mod.  It
simply consists of a small piece of PC board containing two capacitors and
an RF choke which comprise a LP filter/matching section.  On the output side
of the PC board is a short piece of hookup wire that pokes into pin 7 of
tube socket V202 (1st mixer cathode).  The input side is the coax cable that
connects to your LF antenna. In operation there is no switching involved as
the LF input comes into play below about 500 KHz (actually is usable above
that frequency).

For the input Coax lead I used the old Coax cable with mini BNC that was
removed from the parts PTO where it had cracked at the PTO body.  It was
long enough to reach the BNC 455KHz IF output jack and that is what I used
for my LF antenna input.  The actual mod suggests using the "Whip" jack for
an LF input but it's an odd connector 8^(

How does it work? VERY WELL, right down to 10KHz the lower limit of my LF
tunable preamplifier.  Oh yes, sensitivity at the input to this mod is very
low as you're bypassing the RF amplifier tube and feeding the cathode of the
first mixer.  I have a 35 dB Tunable pre-amplifier which also contains a 500
KHz low pass filter.  With that unit the R-390A makes a decent LF set.  BUT,
it is a little tedious on the wrist if you chase beacons for lone periods of
time like I do 8^)
73 de Phil, KO6BB

****************************************************
*  DXing THE WORLD WITH THE FOLLOWING EQUIPMENT.   *
*  RECEIVERS (all overhauled as needed):           *
*    '67 EAC R-390/URR Surplus Receiver.           *
*    YAESU VR-5000 Wideband, 100KHz-2600 MHz.      *
*    REALISTIC DX-392,  KNIGHT-KIT R-100A.         *
*    Home built Longwave "Hybrid" CW receiver.     *
*    Others which pass thru or are waiting repair. *
*  ANTENNAS:                                       *
*    Coil Loaded 18.5 Meter Long Sloper.           *
*    Roof mounted Hustler 6BTV 6 band Vertical.    *
*    Scantenna Scanner antenna at 7 Meters high.   *
*  LOCATION: Merced, Central California.           *
****************************************************




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