I need a little bit of help here.
It might seem a basic question but how does parallel connecting a twin triode
affect the curves ie what do I need to do to the scales on the graph
The reason I ask is that I want to use the 6A6 as an input, driver for the PX25 and reduce the number of stages to two. This is an initial idea to see if it works and basically to make the breadboard easier and quicker to build so I can get down to some experiments.
I've posted the 6A6 triode curves below, and as we can see that using an HT of 250V with an anode voltage of around 185V and a grid bias of -3V at 3.5mA we get a very nice operating point if we use a 20K load resistor.
Using the full output of a CD player gives a 70V pk-pk swing into the grid of the PX25. So biasing the PX at 35 grid volts with 400VHT will allow it to develop near full power.
It looks nice on paper (to me anyway) but the question is if the valve is parallelled (ignoring Miller cap for now) is it just the current scale that doubles, leaving the grid lines at their existing slopes, and the gain the same, giving me a bias at 7mA rather than 3.5, which will mean halving the cathode resistor?
I know I've probably answered my own question here but I am sufficiently unsure as to need to check before proceeding as I have never dealt with parallelled twin triodes before. I have no choice with this valve as the cathodes are commoned internally.
Steve
