(04-03-2017, 09:10 AM)ppppenguin Wrote: Roughly Hfe x emitter resistor in parallel with 5M6. Since Hfe is highly variable let's say 200 for a BC109, so 4M or so in parallel with 5M6. Say 2.2M with a pretty wide variation due to Hfe.
Haven't taken into account the CR network which is presumably for getting rid of RF or possibly for tone correction. At higher frequencies the impedance will be lower.
beta x emitter resistor is 200 x 2.2k = 440k ~ 400k not 4M. So input R ~ 370k absolutely dominated by the poorly defined value of beta.
Craig
