Errata for "The Hybrid Cascode--A General Purpose AGC IF Amplifier"

Page 31, middle column, four lines down from the top.      The memory capacitor is described as C3.    It should be C16.   (10Nov07)    

Page 32, Fig 4 Caption.    There are nine diodes in the circuit, so the bill of materials should list D1-D9.   (13Nov07)    

Page 32, Fig 4 Caption.     The bill of materials neglected to list U1, which is a LM317L programmable regulator.     Also missing are the three JFETs, Q2, Q4, and Q6.   These are all type J310.     (17Nov07)    

Page 31, right hand column, 3.0 inches up from the bottom.    We made the comment that "If necessary, R5 may be increased to slow the attack."    The was a poor choice of words.    If R5 is increased, it will decrease the rate that charge is changed across the capacitor, but it will actually make the attack faster.    In the extreme it could lead to a severe overshoot.    This problem can be fixed with addition of another capacitor from the cathode of D6 to ground.     (The "ditter" pulse modulator [EMRFD, Chapter 7] that was used to test the design is really a useful tool for this sort of circuit.)   (23Nov07)    

Page 33, Fig 4.   Add a resistor, R37,  from the AGC line to a pad at the edge of the board.    The value is 10K, but is not terribly critical.   This is a point that will drive the S-meter circuit described on the applications page.     Also add a pad at the board edge and connect it to the 9 volt regulated output from U1.   This voltage is used in the S-Meter driver circuit.  (2Dec07)      

Pages 32 & 33, Fig 4.    Several component changes are suggested to enhance overall stability and to enhance the buildability of a PC board version of the design.   Technical details are found by clicking here.    (1)  Replace L2, L3, and L4 with 47 uH RF chokes.   We use Mouser part number 542-77F470-RC.   (2) Change R1 from 2.2 K to 1K.    (3)  Add an 18 or 22 Ohm resistor, R38, in series with C12.     There is no slot for this resistor on the boards from KA7EXM, so it will be necessary to stand C12 and the R38 on a single lead in the holes formerly used by C12.   The two components are then soldered together in mid air.   Keep the leads short and you will never notice it.   (3Dec07)  

Page 32, Fig 4.   This is a modification to simplify the buildability and does not relate to a problem.    Replace L1, a 7.1 uH toroid inductor, with a 6.8 uH RF Choke with a Q of 50 or more.    The choke we picked has a Mouser part number of 434-22-6R8.    I measured Q at 9 MHz of over 70.  The self resonant frequency for this choke was 111 MHz.     Also, change R7 from 3.3 to 3.0 K to improve the input impedance match.    (2Dec07)  

Page 32, Fig 4.   R15 can change to a 3.0 K.   (It was 3.3K and this change will have minimal impact on performance, but it keeps the cost down on the kitlet offered by KA7EXM.)        (3Dec07)