[HBR] Small 100Khz IF transformers

[Sandy and Kees Talen]

Just got through testing a few JW Miller 15-H, K-TRAN, 262Khz
IF transformers. These are the small 3/4" square units (same 
physical size as used on the HBR-11/12/13). These were 
originally designed for 6BE6 and 6BA6 IF tubes.  

Coil inductance actually goes from about 2mH to 6mH which really 
surprises me that it will go that high. They are set at approx 3.5mH 
for the 262Khz frequency. The resonating capacitor integtated into
the base ranges from 80-95pf.  
 
The coils are very densely wound (something I can't do yet with the 
coil winder) using approx 37 feet of #40 wire (not bifilar .....which
surprises me a little). There is no room to add windings to the 
diameter of the coil (will contact the powdered iron cup), but there is 
a possibility of adding additional turns to the ends of the coil. The 
cup provides higher permeability and self shielding, something the 
JW Miller #1710 and #1709 don't have, requiring a flexible powdered 
iron material inside the can.

At 95% of the maximum inductance (should be lower to allow tuning 
room) the coil "Q" is "74" which is very close to what the 100Khz 
JW miller IFs measure.

Calculations show that a 430pf padder added to the 80-95pf internal
capacitor will bring it to 100Khz. This is more capacitance than 
I would normally add as additional padder, however the starting 
point is 80-95pf. This brings the total to approx 520pf.....that's high. 
The JW Miller 100Khz IFs use 333pf. Need to make some more 
"Q" compares but my JW Miller #1710 is about useless (patched 
broken wires at the coil 3 times) due to the multiple times removing 
it from the can, unsoldering wires, etc.

All the above said, the Spectrum Analyzer does not lie (the real circuit
application would be better) and at -6dB, the BW is 3.8Khz and the 
-20dB BW is 19.2Khz ....really pretty good. The JW Miller #1710 is 
measured at 3.5Khz and 15Khz. You can add another IF stage and 
put two IFs in series (HBR-13). The overall insertion loss is greater 
than the #1710 but .....close enough. 

Since the #1710 and #1709 transformers are "unobtanium", these 
JW Miller 15-H IFs should be more readily available (used in many
car radios) and ought to work ....and they have the cool JW Miller 
label just like the #1710 and #1709.  

73s  Kees K5BCQ