Circuit Boards for the
Hybrid Cascode General Purpose AGC IF Amplifier
w7zoi & wa7mlh, QST, December, 2007 pp 30-33.

(11Nov to 12Dec07, 2Jan08)    

Click here for errata.  (latest 3Dec07)
Click here for applications information (Modifications, S-Meter, Crystal Filters, Output Attenuation)   (2Jan08)  
Click here to see a discussion of some stability issues.      (2Dec07)

Roger, KA7EXM, has circuit boards and kitlets.  Click http://www.ka7exm.net/ to see the details.   Photos are shown below.  We made a few minor modifications to the design to help the builder.   You can see these in the applications page and the errata page.  A schematic is shown below.     
    We use the term kitlet to differentiate this from a full form kit.   That is, Roger offers a PC board and a collection of parts for the design, but it is still a homebrew project.   The builder/experimenter is still part of the process.   The kitlet includes a circuit board.   There are no step-by-step instructions.

 

One of Roger's boards loaded with components.   This was a "test" version of the kitlet.    The resistors were purchased as 1/4 Watt, but have a size much like the 0.1 or 0.125 Watt units of the past.   Even if the dissipation rating is only 0.1 W, that won't be a problem, for none of the parts are stressed.   (The two resistors in the upper right corner are traditional 1/4 W so you can compare.)   The pot is mounted on the board.    The board layout accommodates this, but the pot will eventually be mounted on a receiver front panel.    Two resistors are replaced with wire jumpers; this was intended.   The pads are there to allow flexibility for the experimenter. No stability problems were noted with this board.    The problem of overall stability is considered by clicking here.   There is nothing critical about the transformer.  Since it is wound on a high permeability core, about any winding style is fine.     The differential pair, Q7 and Q8, are on the right side of the board about half way up from the bottom.   The modification "TeePee" is seen just above the pair.   See the errata for details.  

At this time we have no plans to offer a SMT version of the board.    If any of you want to build a SMT version, write and I'll share my layout.


This is the left side of the schematic diagram, as built from one of Roger's kitlets of parts.


And this is the right hand side of the schematic.   There are minor differences from the QST schematic.
  
Again, to all of you who have written, thank you very much for the comments and for the feedback you provided.   It has helped us to decided upon a course of action regarding a printed circuit board offering.

Click here to see errata for the December 2007 QST article.