[HBR] IF Transformer Theory Questions

[Byron Tatum]

Thanks Dan. I have obtained the Meissner book, thanks a lot! Byron.
----- Original Message ----- 
From: <Hopperdhh at aol.com>
To: <hbr at mailman.qth.net>
Sent: Friday, October 05, 2007 7:17 AM
Subject: Re: [HBR] IF Transformer Theory Questions


> BJ,
>
> Very good questions!
>
> I'll take a crack at your first question.
>
> The difference in selectivity is due to whether the capacitive coupling 
> aids
> or opposes the inductive coupling.  In tube type high impedance circuits, 
> even
> 1/4 to 1/2 pF of capacitance between the two coils can make a big 
> difference
> in the response of the transformer.
>
> A good reference and a very complete answer to your question can be found 
> in
> the Meissner "How to Build" Instruction Manual (copyright 1943) reprinted 
> by
> Lindsay Publications Inc, Manteno, IL.
>
> For the second part of question 1: For economic reasons both coils are
> usually wound at the same time, therefore in the same direction.  The 
> coupling
> coefficient would be the same if they were wound in the opposite 
> directions.
>
> 73,
>
> Dan Hopper K9WEK
>
>
>
> In a message dated 10/4/2007 8:58:08 PM Eastern Standard Time,
> bjtatum1 at peoplepc.com writes:
> Hello-
> If I could bother anyone with the knowledge and experience in working with
> tube circuit IF transformers I would like some help in these areas: (455 
> KC
> units)
> 1. The subject of reversing the leads of one coil, and said coil is wound 
> in
> opposite direction of other coil. I noticed this done on an IF 
> transformer, in
> comparing it with a very similiar one using the same coils, same spacing,
> perm tuned, and same fixed capacitors. The former transformer was rated at 
> 9 KC
> selectivity at 6 dB down (diode transf.), the latter was rated at 12 KC
> selectivity at 6 dB down (input / interstage transf.).
> What occurs if you simply build an IF transformer with coils wound in
> opposite directions, is the coupling greatly reduced? Is this why they 
> also swapped
> the leads around on the coil wound in opposite direction, to only slightly
> reduce the coupling and gain an improvement in selectivity?
>
>
>
>
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