I'm playing around with a cascode configuration using 2 of the three triodes in an 'AK10 compactron. Once I get it worked out the third will be used as a concertina to drive something PP (not sure yet what I want to put there).
To keep the distortion down the lower cathode is not bypassed which cuts the gain about 2/3 (~160X to ~60X). Don't really need a lot, but I was looking around for ways to get some gain back and found a few references to adding a shunt resistor from B+ to the plate of the lower tube. This worked really well. The gain went up ~25% (all on the lower tube) with absolutely no change in distortion at the top. If anything it got a little better. This is like something for nothing, more gain and no increase in distortion.
So why don't I see this more often in circuits? Does it only help for tubes that want a fair amount of current? 'AK10 is rated for nominal 10ma on the plate.
I can draw up a schematic if it's needed, but this is pretty much a generic cascode, except with a resistor from B+ to the point where the tubes connect plate to cathode.
To keep the distortion down the lower cathode is not bypassed which cuts the gain about 2/3 (~160X to ~60X). Don't really need a lot, but I was looking around for ways to get some gain back and found a few references to adding a shunt resistor from B+ to the plate of the lower tube. This worked really well. The gain went up ~25% (all on the lower tube) with absolutely no change in distortion at the top. If anything it got a little better. This is like something for nothing, more gain and no increase in distortion.
So why don't I see this more often in circuits? Does it only help for tubes that want a fair amount of current? 'AK10 is rated for nominal 10ma on the plate.
I can draw up a schematic if it's needed, but this is pretty much a generic cascode, except with a resistor from B+ to the point where the tubes connect plate to cathode.