[ARC5] PRC-77 Surprise

[J Mcvey]

Not sure what you mean by "the circuit being the same". 
You can't sub a npn for a pnp by just swapping the emitter and collector leads.That would make a class A  into an emitter follower and the bias / feedback, etc would be wrong.There has to be subtle differences in the foil patterns and components, even though they may LOOK similar.
Also, the early pnp transistors were germaiium, while the NPN types were most likely silicon.They have different bias requirements.
You could, however, flip the rail polarity and transistor types with some resistor changes.Still the collectors would have the same load in both cases, for example.
 

    On Tuesday, November 8, 2016 6:57 PM, Robert Eleazer <releazer at earthlink.net> wrote:
 

  I have a PRC-77 with a dead 5.6 MHZ IF module.  I took a look at it to see if I could figure out what is wrong and had a surprise. It seems the earlier design of the module, used in the PRC-25 and presumably early model PRC-77's, used PNP transistors.  The later version used NPN transistors, 2N918's.  The two different module designs are interchangeable and the circuits are essentially identical, even to parts placement, except for how the two transistors are connected, emitters either to ground or to the B+ supply. I have never thought of having two circuits that were the same but that used PNP versus NPN transistors.  And it led to some head scratching for me, too.  I thought my old Sylvania transistor substitute guide was wrong for while there.
WayneWB5WSB       
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