Tremolo layout on 6gk6 conversion amp

[8wattjack]

1

[tubeswell]

Its usual to have a depth pot as a voltage divider at the LFO stage's output. With the pot rotation antiCW, the pot wiper/trem insertion node should be 'grounded' (or referenced to the bias voltage of a fixed bias stage). With the pot rotation fully CW, the pot wiper is at the ungrounded end of the pot resistance, where the potential is moving up and down.


The speed pot can be added in series with one of the resistors in the plate-to-grid C/R network. If another one of these resistors is jumped to the cathode of the LFO stage (instead of the ground return), if will 'kick-start' the trem when you turn it on. The footswitch can be used to ground one of the caps in the C/R network.

[sluckey]

how can it have no coupling capacitor between the last preamp to the phase inverter?

It's called dc coupling, direct from previous plate to grid of next stage. It's actually quite common when coupling to a cathodyne PI or cathode follower.

Intensity pot depends on how you will inject the tremolo signal into the amp. Your incomplete schematics don't show that. How will you do yours?

[PRR]

> not sure why the oscillator loop has an extra c/r in the network. it must not shift the full 60 degrees in each c/r section maybe?

You need 180 degree shift. If there is enough gain, this will happen.

Two R-C can not-quite reach 180 deg. Even a gain of infinity won't oscillate.

Three R-C can approach 270 deg, and will pass 180 deg with a loss about 27. Amplifier gain over 27 will oscillate.

Four R-C can approach 360 deg and will pass 180 deg at quite low loss, maybe 4? So you don't need much of an amplifier to make it ring.

The flip-side is the extra R-C parts.

BUT -- AND -- if you want to VARY the frequency (tremolo rate) with a single pot --- one variable resistor in a 3 RC network gives very small change, one variable resistor in a 4 RC network gives even less range. As it works out, trem usually does not need a huge range. If one of three Rs change 10:1 (200K to 2Meg) we get 2:1 range, which apparently means we can "match tempo" with the musical beat (or a 2:1 ratio faster or slower). We can often get a 20:1 resistor range and 2.8:1 speed change. One variable resistor in the 4-RC network only gives 1.77:1 to 2.1:1 rate range.

And back off. This is an ORGAN trem. Organists often live with no Depth or Rate control. (The original mechanical shutters in front of a box of pipes could not manage this complexity.) You are an electric guitarist. IMHO you want a guitar-adapted tremolo plan with wide range of depth and rate to match your wild-to-mild musical stylings.