[Hallicrafters] I "Stabilized" my SX-71 some

[WA1KBQ at aol.com]

The SX-71 was Hallicrafters first dual conversion receiver and featured a 
narrower more defined pass band than any of their previous offerings. I don't 
remember what it was offhand but am guessing it's in the neighborhood of 3.0 
KC's. For this reason drifting will be more noticeable and audio quality on AM 
will not be as good as that on earlier models or models with wider passband 
capability. I don't remember where I read about the SX-71's new narrower passband 
whether in the manual, a bulletin or an advertising brochure but I used to 
listen to an SX-71 every day. While I don't remember the drift being unacceptable 
after warm-up the narrow passband made you tired of listening to AM after a 
while. The SX-71 is back upstairs stored away in a box now and an NC-400 is 
currently performing the daily chore of band monitoring here in the shop. It 
drifted a lot at first and for whatever reason just swapping the 0B2 made a huge 
difference. I noticed the degree they lit up orange was different with the 
different tubes I tried and settled on one that drifted the least. I have not had 
time to check further into that yet but I will pull it from the cabinet and 
check the tube pin voltages to see if we can figure out why the sensitivity with 
the 0B2.

73, 
Greg Gore; WA1KBQ
Charlotte, NC