more depth from vibrato circuit

[danotron]

I am using this circuit in an amp and would like to get more depth from it. Does anyone have any suggestions as to where to tweak it?.....new component values?

[Phil_S]

I'm uncertain about circuit tweaking. This type of circuit is all about voltage swing and triggering oscillation.

Before you get into changing the circuit... The plate resistance of the tube is a big factor in triggering oscillation in the circuit. Basically, 12AU7 and 12AT7 won't trigger. 12AY7 is borderline and probably inadequate. 5751 might work, but not particularly well.

Get a good strong new production 12AX7 and try that first. Maybe nothing will change and maybe you'll get a surprise.

The other thing you might work with is bias voltage on your power tubes. A small change there could have a ripple effect on the tremolo. What you are showing is a bias modulated tremolo. The two are intertwined.

[LOUDthud]

Bias modulated tremolo usually requires the bias be set on the cold side to get good depth.

[tubeswell]

You could try the Blonde Tremolux circuit values - 6G9B (which also eliminates some of the padding). These are designed to run with a lower bias voltage. But as LOUDthud says, cooling the bias off makes bias-vary trem come alive more.

[Structo]

That .01uf cap between the two 1M resistors on the left is the one to change.
It will make it slower if you change it to larger values.
Such as .015uf - .022uf.

Then the .1uf caps by the Intensity pot for deeper.

[jjman]

To strengthen mine I reduced the 470k between the cathode and the junction of the 2- .1 caps on my setup. Maybe to 220k.