6G7-A Bandmaster tremolo

[Randall]

I am looking at my first ever blonde Bandmaster with three tubes for the tremolo and no photo resistor. I am not seeing how this works, could someone explain it to me in general terms? It is not broken on this amp, it actually sounds great.

http://ampwares.com/schematics/bandmaster_6g7a.pdf

[Enzo]

First 12AX7 is classic oscillator and a cathode follower to send trem to the intensity control. From the control to the next triode, which is a phase inverter, sending two copies of the trem at opposite polarities on to the next 12AX7. Note the signal from the preamp comes to the upper grid through a 0.00025 cap (250pf) meaning mostly highs, but the signal also splits through the 220k and 0.005uf cap to the other grid, lower end. Meanwhile, the trem signal is hitting both those grids as well. That big signal is yanking those grids up and down, affecting their bias points. This has the net effect of altering teh signal level at the plates of the 7025, those signals mix back together in the 470k resistors and on into the power amp.

[Randall]

Enzo, that makes perfect sense. Thank you once again. I think the magic of the tremolo sound in this circuit has to do with the crossover splitting of the signal and then mixing them back, am I right?

[Enzo]

I'd say, and the highs and lows are tremming opposite one another rather than all at once like usual.

[Jazz P Bass]

Thankyou, Enzo.

[Gingertube]

I have been experimenting with different tremolo circuits searching for that "ultimate" lush tremolo sound.
Best I've managed so far is the Gibson GA40 Les Paul circuit BUT that requires pentode Input Tube (I use 6BR7 rather than the originally specified pentode).

Is this 6G7-A tremolo in the "lush" vein. Is it worth adding into an existing amp for a trial?

Thanks,
Ian

[Reader]

- - - Is this 6G7-A tremolo in the "lush" vein. Is it worth adding into an existing amp for a trial?
Thanks,
Ian

I think that's hard to answer because different people will have different definitions of lush. A well working three tube Fender tremolo is unique in my opinion. I like to cal it "Shimmering." The circuitry needs to be well balanced or the amp will pump the speakers at the LFO frequency. It can get pretty bad when the circuit sections are out of trim. I will say that, when I hear this type of tremolo that is working properly, I really like it. If you have the resources, I say it would be a good project to build.

[Gingertube]

Thanks,
I can see that there is no LFO signal filtering at all, and it is relying on that 3rd tube (the 7025) having closely matched triodes so the out of phase LFO components cancel at the summing point of the 2 x 470K resistors.
Cheers,
Ian

[pdf64]

I'd say, and the highs and lows are tremming opposite one another rather than all at once like usual.

That's how I used to see it too, but Roly's analysis at https://www.guitargear.net.au/discus...?topic=30731.0 puts it in a different light.
I came across it when I was trying to work out how the excellent Vox vibrato worked (I've never knowingly heard a Fender harmonic vibrato).

[Jazz P Bass]

Very enlightening post (link).
Thanks.