by EWBrown » Mon Oct 22, 2007 6:13 am
The "forked" approach offers better DC power isolation between the VA and PI sections of the first tube
Even though the DC voltages are the same, the current consumptions of the two sections are different, hence the two differing resistance values.
A quick application of Ohm's law indicates about 4.5 mA for the VA and 7 mA for the PI stage.
WIth the resistors in series (let's say 22K and 11K), the VA and PI stages would receive different B+ voltages, and the VA's 47K plate resistor would have ot be decreased, lowering that stage's gain (not a good thing).
Since the plate of the VA is direct-coupled to the grid of the PI, these voltages have to held very closely, in order not to create a serious imbalance inthe PI.
HTH
/ed B in NH
Real Radios Glow in the Dark