I'm trying to fully understand some tuned amplifier circuits and i guess this should be really simple to you guys.Here are them:
I would like ask you three things things, each one regarded to each circuit :
Circuit 1 - Here i understand the upper transformer is meant to do a coupling to the final stage ( how does a transformer coupling help ? ) .Am i right that the final stage is a selective filter that is necessary to have so that in Vo we get only the frequency we want ? I also want to understand why do we need to put a capacitor in paralel with Vin before throwing the signal into the lower transformer.
Circuit 2 - I don't see clearly what L3 and C2 are doing, do they form a tank ( selective filter ) ? , why would we need a tank there ? The only thing i know C3 is meant to block the AC for the bias.
Circuit 3 - Okay, now in initial stage we got a input current, does it change anything? Also, in the final stage we have not a RLC circuit, but a RL filter ... Does that change anything or has any purpose ?
Thanks a lot in advance.