[Hallicrafters] Fw: SX-101A VS SX-115

[Harry Vaught, KT4AE]

I've never had an SX-115, but I've had some SX-117's and an SX-101A.

Back in the Spring, I cured essentially all the drift in my SX-101A - 
almost accidentally.  After a 45 minute QSO on 15 meters where I was 
chasing the other guy up and down within about a 2 kc range I did the 
following:

I replaced the 12BY7 oscillator with a new tube. This shifted the 
calibration by about 20 kc.  I took the hood off the main tuning cap, 
properly indexed the dial pointer and then re-aligned the RF coils to 
correct the calibration.  I didn't fool with the soldered trimmers.

After this, given a few minutes warmup, it's almost as stable as an 
SX-117 (my current one is rock solid).  As an added side benefit, dial 
tracking is much improved.

I think it may be largely luck that determines which 12BY7 is going to 
be a stable one.  I've had this receiver about 13 years and have 
replaced the 12BY7 a number of times without notable change in the 
drift.  I usually leave it plugged in so the 12BY7 is hot and the heater 
is on.  I unplugged it a week go when we went out of town for the 
weekend.  When I plug it back in, I'm going to check and see how long it 
takes to become stable again.

Harry, KT4AE
Maryville, Tennessee