[HBR] Cascading IFs

[match at ece.utah.edu]

On 19 Aug 2008 at 4:01, hbr-request at mailman.qth.net wrote:

> Hello Group!
> 
> I was wondering about cascading two 85kc R-23 IFTs for a better shape
> factor.  My plan was to use two transformers after the last mixer in
> cascade.  Has anyone here tried this?  I've seen it suggested on the
> HBR webpages, but can't find much practical info beyond that. What is
> the best means to couple the transformers, I assume top capacitive is
> the least desired method.; with some sort of inductive bottom coupling
> being the most desirable?
> 
> One other idea that's kicking around in my head is to use two of the
> IFTs that had the lower impedance tap for the diode load at this
> point.  My thinking was to have these two low impedance windings as
> the secondary for T1, and as the primary for T2.  I would then use the
> T-Notch circuit for coupling between the stages;  I've even considered
> flipping those windings to make the tap point lower (to achieve even
> lower impedance points used for coupling between stages) to see if
> that improved the performance of a T-Notch circuit between those two
> points.
> 
> There are days I really feel that I started this project about 40
> years too late. :(
> 
> Pete

I had intended to use a pair or even 3 6EH7's in my IF strip, and running 
cascaded pairs of these transformers at the first 2 coupling points. That 
would be 6 transformers total. But now I'm thinking that a strip with 3 or 4 
6BJ6s would be easier to tame. I'll breadboard both and run some tests, I 
suppose.

There's nothing particularly magical about the coupling scheme used, as far 
as I know. Capacitive top coupling is the easiest and cheapest requiring only 
a small cap. Bottom inductive coupling would require taking the transformers 
apart.

Marvin
KA7TPH