[Hallicrafters] Hallicrafters 50KC IF Amplifier Design

[WA1KBQ at aol.com]

Litz wire came into popular use as an outgrowth of the great "Low Loss Era" 
 which got its start in 1926. In those days the rage was all about 
experimenting  with coil design and winding strategy (toroid, basket weave, 
binocular) in order  to find the best coil design with the lowest possible loss. All 
early  superheterodyne IF transformers had air cores (some were wound  on 
wooden dowels) and were compression mica or air tuned so Litz was  preferred 
to increase "Q" and reduce loss. In late 1935 Aladdin iron  core IF 
transformers made their appearance on the scene in the Hallicrafters  SX-9 which 
made continued use of Litz unnecessary. With iron cores  now available and 
eventually permeability tuning, single strand  winding was good enough to meet 
engineering requirements and less expensive. As  far as I know there are no 
ferrite core Litz wound transformers in any  commercially produced 
communications receiver other than the SX-88 and I welcome  anyone to correct me on 
this. 

The SX-88 returned to Litz winding for the  50KC transformers but now 
featured new threaded ferrite cores and coils  inside ferrite sleeves to boost 
"Q" to the 175 to 185 range. SX-88  is the only 50KC equipped Halli with no 
threaded brass adjuster rods  sticking out of the top of the transformers. 
Other than the SX-88  every Hallicrafters 50KC IF transformer out there has 
single strand winding  with a brass adjuster rod and has a "Q" of around 100. 
This  is true of the much acclaimed SX-115 also. What happens when  you 
insert a piece of brass into a coil? 
 
Greg Gore; WA1KBQ