[HBR] Small 100Khz IF transformers

[Bob Duckworth, WB4MNF]

Kees-

Have you given any thought to using two of these 262 coils?
Place the windings in series on each and wind yourself a link
coil on each, between the windings. Use this link coil as your
coupling between the two tuned circuits. If you experiment a
bit, you can likely stick a cap across the link to vary bandwidth.

I've not built this, just a thought. I get them sometimes
when it's still early in the AM and I've just had my morning coffee :-)

73,
-bob
wb4mnf

Sandy and Kees Talen wrote:

> 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
> 
> 
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