[Hammarlund] AADE Digital display for SP-600 WORKS!

[Philip Atchley]

Hi All,

Well, after a number of hours of working on it, I got this little 
critter to work properly.  As I mentioned in an earlier Email, I'd tried 
tapping the LO at both the grid and the plate connection.,  Finally I 
made a "gimmick capacitor" off the lead going to the FCU switch, to feed 
my Source Follower "Isolation amplifier", but STILL had problems.  Last 
night I even put a small pot on the BNC connector input of the unit so I 
could adjust the level.

This confirmed ONE thing.  I had plenty of signal, at least on the low 
bands.  That because if I turned it up all the way it would read a 900kc 
tuned frequency as over 2MC (apparently the 2nd harmonic of the LO). 
Turning it down about halfway and the three lower bands worked PERFECTLY!

HOWEVER, the readings were still very erratic on the three higher bands. 
  I could often make it read anything I wanted from the "real" frequency 
to about +/- 15-20kc.  Not what I would call a stable circuit.

THEN, this morning I removed the "tweak" jumper from the display board 
and things settled down to a nice steady reading of exactly what it 
should be!! That "tweak" jumper activates two small, 25turn pots that 
allow you to "tweak" the unit to allow for Xtal Filter errors and a 
second LO Xtal that is off frequency.

NOW, it reads correctly, but is about 200Hz off on BOTH the low and high 
bands, this probably due to a drifted Xtal filter.  I CAN LIVE WITH 
200CPS ERROR!

So far it appears to be working exactly as it should, with no 
instabilities, but time will tell.

One other thing I noticed is that it no longer reads up to 53MC (it's 
specked to 40MC).  I 'might' be able to get it to read higher by 
adjusting the input pot, but I'm going to leave well enough alone ;-)


73 de Phil  KO6BB
My DXing tools (RECEIVERS), all fully overhauled:
    Hammarlund SP-600 R-274C/FRR, 18 tubes (Circa 1952)
    National NC-60 Special, 5 tubes (Circa 1960)
    Heathkit Mohican  (Circa 1962)
    Icom IC-751 Digital Transceiver  (Circa 1986)
    Grundig S350 Digital Portable (Circa 2004)

THE BEACONEER'S LAIR:  http://www.geocities.com/ko6bb/
QSL GALLERY: http://photobucket.com/albums/y123/KO6BB/
Merced, Central California,    37.3N  120.48W  CM97sh

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