With no other info, you have competing requirements.
You have a paraphase (2 triodes), and want a free triode. Split-load looks like only 1 triode, but when there is a feedback loop, it is always connected to the triode ahead of the split-load inverter. Since the split-load has no gain on its own, it always has what I consider a "pre-gain stage" in the triode right before it.
The paraphase doesn't have the full gain of both triodes. Generally, the first triode makes full gain, then the output signal is knocked down by the amount of gain of the second triode. End result is 2 signals, opposite phase, and as-big as they would be if amplified by 1 triode.
A split-load with a pre-gain stage will arrive at essentially the same-gain as a paraphase inverter.
You also want to add a NFB loop. Negative feedback works by throwing away excess gain to get less distortion. The presence control reduces the amount of throw-away of treble sounds to get the effect of a treble boost. So you need more gain than you have now to have enough to add feedback and still be able to drive the output tubes as easily as before.
By the way, the long-tail inverter will likely have roughly same-gain as the other 2 setups. From input to 1 output only, you get about half the gain you'd expect of that type of triode.
But I can't say for sure which inverter will work for you. It's more complicated than that, and depends on how big of a drive signal the output tubes need and how much supply voltage you have available. We need a schematic.
The best way to get your extra triode will be from an unused effect, i.e., tremolo or reverb. If you don't have those handy, there may need to be major surgery to truly add gain or negative feedback.
Topic: Another dumb question (Read 3325 times)