Single-knob Power Scaling

[makinrose]

Hi Guys

There are a number of similar-seeming 2-triode splitters that might all be loosely referred to as "see-saws".

In TUT Fig..6-11, the first figure shows two independent gain stages where the first stage drives one output tube and also a voltage divider. The voltage divider feeds the second stage to drive the other side of a push-pull output stage. There, the voltage divider is specified to match the free-running gain of the second stage - pretty chancy.

In the context of the single-knob Power Scale solution, a pot sect can be placed at the output of the first stage which would feed both its side of the power stage and the voltage divider. The latter would have to be comprised of high-value resistors to not later the sweep of the pot too much.

The right-hand figure uses a free-running stage to drive one output tube and to drive a feedback-controlled inverter stage. The inverter has a gain of -1 and drives the second half of the output stage.related This circuit is intended to provide accurate signal amplitudes to the output tubes. Again, half the PS pot can be used at the output of the first stage, driving both its related power tube grid and the input to the inverter stage. To not alter the pot sweep too much, the gain-set resistors for the inverter have to be quite high.

Any variations of splitter design where the stages are interconnected at the cathode will require a 2-section pot for the drive compensation function unless a single-section is used ahead of the entire circuit.

Have fun

I was referring to the type of splitter on the left hand side of TUT Figure 6-11.  Most usually in Fender, Valco and Gibson amps of that era  I'll see R1 and R2 act as the grid leak for output tube one and a voltage divider for the second drive line.  

I have tried the single pot approach you suggested but wasn't happy with the sound...I may need to further play with the values I used though. 

If I were to use a dual pot rather than a single pot would I use a R1 and R2 (from Figure 6-11)  as a voltage divider but not a grid leak for output tube and then replace the two grid leaks with pots?  Maybe a bit like figure 6-38 in TUT 4 but with a dual pot for the 100K grid leaks?