Tube tremolo with 12AX7(high voltage)

[duck_arse]

gtudoran - you have me puzzled, dazed and confused, now. doesn't your diagram show the two cathodes shorted together?

and the seven pin socket, BAH! (the valves were very cheap.)

[gtudoran]

Yes, that is true, but as i said it's not the final version. And i would like to implement at least a 2 level of depth using a switch and that can be implemented only (in this case) by varying the resistance in the cathode of the LFO and that would be kinda hard to do that if the cathode is common.
I don't know how it would behave if you would change the resistance for both stages (i do think that would work ok because all in all both cathodes are tied).
So on a second thought it should work ok. You can make an experiment and see. But i do think that it should work. Regarding my statement "a little bit tricky with the common cathode" i was thinking on other applications then this one.
But, at least for me, i would stay inside  common tubes circle because of the compatibility (i'm thinking for a small run of units) but for personal use ... you can use any tube models.
So .. ya... it should work

Regards,
DeX

gtudoran - you have me puzzled, dazed and confused, now. doesn't your diagram show the two cathodes shorted together?

and the seven pin socket, BAH! (the valves were very cheap.)

[PRR]

> depth ... can be implemented only (in this case) by varying the resistance in the cathode of the LFO and that would be kinda hard to do that if the cathode is common.

OR by varying R5 (LFO plate resistor). Or LFO supply voltage. Either will reduce LFO current, which is the real thing which needs to be varied.

R5 might have to be over 1Meg, which is awkward. It also may want to be Reverse Audio for "normal action", awkward. True, there's a semi-common part for Fender trem (rate) which is several-Meg RA taper. This might also work at your "rate" pot, keeping inventory and assembly simpler.

Hmmmm... too-clever depth tricks like this may also affect speed.

[thermionix]

there's a semi-common part for Fender trem (rate) which is several-Meg RA taper.

https://www.tubesandmore.com/products/R-VC3M-RA

(no association)

[merlinb]

And i would like to implement at least a 2 level of depth using a switch and that can be implemented only (in this case) by varying the resistance in the cathode of the LFO and that would be kinda hard to do that if the cathode is common.

You don't have to vary the DC resistance, only the AC impedance. e.g., use a huge capacitor (1000uF) in series with your depth pot. This allows you to vary the amount of cathode decoupling from little to lots. Also stops the scratchyness that DC variations would cause.

[gtudoran]

Thank you Merlin, i will try that this weekend and see how it goes (didn't thought of that ... in my head was only DC and no AC ) )

Regards,
DeX

And i would like to implement at least a 2 level of depth using a switch and that can be implemented only (in this case) by varying the resistance in the cathode of the LFO and that would be kinda hard to do that if the cathode is common.

You don't have to vary the DC resistance, only the AC impedance. e.g., use a huge capacitor (1000uF) in series with your depth pot. This allows you to vary the amount of cathode decoupling from little to lots. Also stops the scratchyness that DC variations would cause.

[duck_arse]

I can report - as drawn, with a 6J6 and B+ of 120V, no percolations are forthcoming.

when I tried 12AX7, I got plenty oscillation, but viewing the output with sig-gen input (after a pair of PRR's r/c's), there was minimal modutation apparent. thoughts?

[merlinb]

when I tried 12AX7, I got plenty oscillation, but viewing the output with sig-gen input (after a pair of PRR's r/c's), there was minimal modutation apparent. thoughts?

As I said earlier, you need a 12AT7 / ECC81. It is more non-linear than a 12AX7, so it will give more modulation. In a pinch, remove R7 and decrease R6. This should increase the depth somewhat, but you're never going to get lush, throbbing trem with a 12AX7 and a simple circuit. If you want lots of modulation you need a variable-gm tube for the gain stage. You'll still need a 12AX7 or 12AT7 for the oscillator tube though, as only they have enough gain.  6J6 will never work in 3-stage oscillator, it doesn't have enough gain.

[gtudoran]

@duck-arse - i will try to update the schematic todat or tomorrow because i've made some modifications that are on breadboard but not on schematic.
And with that mods seems to me that i have enough depth in sound. The schematic was modified quite a lot - my B+ was 250V-280V if i remember well.
I hope i can get to the shop today and translate what is on the board with what is on the schematic.

Regards,
DeX

[PRR]

> with a 6J6 ..., no percolations

I think you were gently told it was unlikely.

To be blunt, I have seen enough 12AX7 fail to wobble reliably in a 3-pole phase-shift oscillator that I would NOT try any lower-Mu device. Maybe 12AT7... it is a spiffy device, and I now see Merlin's endorsement. But the 12AX7 wobbulator is easily plagiarized from millions of guitar amps.

[duck_arse]

told, I was indeed. but, of course, I still went and tried it. other cats/skinning methods ....

[thermionix]

But the 12AX7 wobbulator is easily plagiarized from millions of guitar amps.

QFT.

I think OP can find a circuit (and waveform) he finds pleasing at slow and fast speeds.