Help Me Design a Tube Vibrato

[frequencycentral]

Sorry for the double post if you read the ' What are the requirements for a Phaser LFO ?' thread.

I'm breadboarding a few ideas at the moment towards a low voltage tube vibrato. I hope also to work the ideas into a low voltage tube phaser.

I'm using 6111 submini tubes, which are similar to 12AU7 but tiny. Each tube heater requires 6.3 volts, so I'm running the heaters for two 6111's in series at 12 volts. This works out fine over extended periods.

I'm using a MAX1044 switched capacitor voltage convertor to get a higher plate voltage from a 12 volt wallwart, as I have found that my cathodyne phase inverter lacks symmetry at 12 volts. It's a lot better at 30 volts. I know the maximum voltage for a MAX1044 should be 10 volts but this works fine.

I want the entire audio path to be tube but I want to use a solid state opamp (or transistor) LFO.

I know I'm getting close, the outputs of the cathodyne phase inverter are nicely out of phase and I get a 30db drop when I mix them.

It's the two output triodes I'm having problems with. I've tried a few different LFOs, buffering then inverting the signal with the opamps shown in the schematics. I'm also looking at two different ways of applying the LFO signal to the triodes - see the two schematics.

The main problem is that the two output triodes are not opening/closing fully - at least one of them isn't. I'm also getting plenty of LFO bleed - ticking - in the audio path.

I don't pretend to be a great designer - I have no formal training and I find the math boggling. But I'm really keen to work this out.

So - please have a look at my schematics and pick fault, suggest improvements etc. I think maybe i need an LFO recommended too, and an effective way to apply it to the triodes.

Here are the schematics:

Version 1 - modulating the triodes through the anode.



Version - modulating the triodes through the cathode.

[snap]

IMHO version1 is an attempt for gridmodulated tremolo