[HBR] IF transformers

[Peter Bertini]

Since I have several of these 85kc transformers to play with, I tried
two in cascade with good results. I tried several different coupling
cap values to couple the secondary of the 1st IFT to the primary of
the second one to see what effect the value would have on the
selectivity, and at what point the coupling became lossy.  Two in
cascade worked fine. I was curious, and added a third transformer, for
three in cascade. I ran into something odd: the two coils in the
middle IFT didn't seem to behave right; as if there was no mutual
coupling between them? This was even with the coils set for max.
coupling, close together. I don't understand what I am seeing. Adding
a small coupling cap from the high end of the primary to secondary LC
circuits in the second IFT solved the coupling problem.

Pete


On Tue, Sep 30, 2008 at 7:47 PM, Peter Bertini
<radioconnection at gmail.com> wrote:
> I'm playing around with the R-23 80kHz transformers. Boy, they don't
> appear to be very high Q, and use a high L to C ratio.  I assume this
> was done to control the bandwidth for AM reception? Also, I have a
> question about the button silver mica caps and the old dogbone style
> ceramic caps that were used.  I know these were good caps back in the
> late 30s and early 40s, but I wonder if it it would be good practice
> to replace them with newer 180pF dipped micas since these components
> are now 60 years old?
>
> Pete
>
> On Sun, Sep 28, 2008 at 9:11 PM, Bob <bob at atl.org> wrote:
>>
>> Harry Lythall - SM0VPO has some homebrew IF transformer
>> info under
>> reference: data technique: DIY IF cans
>>
>> http://web.telia.com/~u85920178/
>>
>> I should have photos of my HBR soon. It's got to go. No more room and if I
>> do well enough this semester to get into nursing school, no time for the
>> next few years.
>>
>> -Bob
>> AH7I Atlanta/Honolulu
>> ************************************
>> Visit the HBR Receiver Web Site with over 100 pictures of receivers and
>> construction notes...... via http://www.qsl.net/k5bcq/
>> there is also a mirror (faster response)at http://k5bcq.edebris.com/
>>
>>
>> Retrieve reflector archived data via http://mailman.qth.net/mailman/listinfo/hbr
>>
>>
>