[Johnson] Invader

[David C. Hallam]

I am currently refurbishing a Pacemaker that has no end of problems.  In the
course of reviewing some of my references, I was reading the Single-Side
Band Communications Handbook by Harry D. Hooton and ran across an
interesting reference to the Invader.

In the book the author states that the Invader was designed to operate with
a crystal microphone and has no DC isolation of the microphone from the
input audio amplifier's grid.  If used with a dynamic microphone, a .005 uF
capacitor should be inserted in the microphone lead to block DC.  Looking at
my Invader schematics, I see this is true in the 1961 schematic.  However, I
guess Johnson recognized the problem and included this capacitor in the
later models as it is on the 1962 schematic.  This change is documented in
the 1962 factory update sheet.

All of this caught my attention because I use Turner dynamic microphones
with my Invaders.

David
KC2JD/4