It compensates for the grid-to-cathode voltage of cathode follower A3V1B.? If I had a 410C, I would connect a shorting jumper across Base-Emitter of A3Q4 to remove all AC signal from the demodulator, then adjust A3R21 so A3V1B cathode is 0V.
HTH,
Dave Wise
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Hi Friends,
I had a second not-working 410C (chopper version) which I left apart. Now I decided to try its repair and I succeeded.
With the opportunity, I tried to understand better its inner working. Even with my limited capabilities, I believe I could understand much of its circuit, but there is something that remains obscure to me.
I am talking about A3R21, its function and how to set it. I could find in the manual only a mention to it in the DC adjustment. In a normal chopper amplifier, the decoder switch just closes to ground; why this extra adjustment? How to deal with it?
Can someone please help me to understand more?
Thanks
Gianni
