Tube based Tremolo Idea

[craftyjam]

I am away from my home lab right now, but I was curious if anyone knew if this type of circuit would have any advantage over a standard bias wiggle trem.
I, like many, have contemplated what to do with the leftover triode in a bias wiggle tremolo.

It's basically just a phase shift oscilator into a cathodyne phase splitter, driving the grid leaks of the power valves seperately.

I realize theres a good possibility that this would just cause one tube to conduct while the other does not, halving the output power.
But I imagine if there was some variation in the amplitude of the two outputs of the cathodyne it could be interesting, right?

Let me know your thoughts, or if this one goes in the trash.

Side Question:
What would happen if you put two halves of two dissimilar triodes in parallel? (12AX7 + 12AT7 etc.)
Which tube determines the gain?

cathodyne trem.PNG

[TUBEDUDE]

I think the net overall change on the secondary side will be no real change at all. Short of driving the output tubes too hard, into cutoff and saturation, the effect should mainly average out.

I shouldn't post before getting up and quaffing that first expresso!

[pdf64]

The point of bias vary trem in a push pull amp is that the modulation signal is common mode, gets largely cancelled out.
With your idea, it’s no longer common mode, as I see it, the speaker will flap like crazy with the subsonics, with only the OT low frequency roll off to attentuate it.

[Stevem]

In fact with the bad effects that can take place like posted in the above reply you could start to argue that you have a Vibrato effect taking place more then a tremolo.

[craftyjam]

The point of bias vary trem in a push pull amp is that the modulation signal is common mode, gets largely cancelled out.
With your idea, it’s no longer common mode, as I see it, the speaker will flap like crazy with the subsonics, with only the OT low frequency roll off to attentuate it.

Ah, ok. So the LFO signal will simply be amplified instead of being cancelled out in the power amp. That makes sense.

So in regards to my second question, if I were to put a 12AX7 in parallel with a 12AT7, how would I determine the gain? I get that ra would just be the two plat resistances in parallel, and gm would be some larger value due to the decrease in plate resistance. Would the gain be closer to the X or the T?

[FUCHSAUDIO]

There is an awesome LND-150 based tremolo on the Hoffman forum. Grid bias and works great ! I made boards for our mods and they work well.
Runs off the choke/screen node, so no special power supply needed. I use surplus Fender 4-M pots for rate and the board mounts via a right angle 16-MM pot for the intensity pot.

[craftyjam]

There is an awesome LND-150 based tremolo on the Hoffman forum. Grid bias and works great ! I made boards for our mods and they work well.
Runs off the choke/screen node, so no special power supply needed. I use surplus Fender 4-M pots for rate and the board mounts via a right angle 16-MM pot for the intensity pot.

Yeah it does, I've built my own LND-150 circuit based on the ac15c1 schematic. Kinda just wanted to do a tube tremolo for the heck of it, even if there are cheaper ways.

[pdf64]

… if I were to put a 12AX7 in parallel with a 12AT7, how would I determine the gain? I get that ra would just be the two plat resistances in parallel, and gm would be some larger value due to the decrease in plate resistance. Would the gain be closer to the X or the T?

I think that the stage gain will be largely set by the larger gm and lower ra.
But bear in mind that the they may not correspond to the typical values noted in the type info, unless the operating point is the same.
eg see https://imgur.com/eKUgKds