Adding tube tremolo circuit to amp

[Bigyouth]

Hello there,

A while back, I built a clone of the selmer little giant. (Please find the schematic attached).

Here also is a schematic of a phase oscillator circuit (with footswitch) from http://www.valvewizard.co.uk/trem1.html that I plan to use.

I'm just not quite sure how to integrate it into the amp. The +300v goes to the B+ (?), and the connection going to the sine wave is the output signal? Where exactly would that go.

Also, is there anything I would need to change on the amp to make this work?

I will try to breadboard the trem circuit before trying to install it.

Advice would be very much appreciated thanks,
Bigyouth

[Phil_S]

In that amp, I think I'd inject the signal into the cathode of the second triode. That's at tube pin, between the tube and the 2200K resistor.

[tubeswell]

For bias-wiggle trem insertion, the tremolo output is taken via a coupling cap from the LFO stage's plate, and can be inserted either at one of the pre-amp gain stage's cathode (e.g. as in the Fender vibrochamp circuit or the Vox AC4 circuit), or otherwise attached to the grid of the output tube.

If you want to get fancier with a dual triode LFO and CF buffer stage, that would work better.

A further alternative would be opto-coupling to the signal path of the amp (as in a BF Fender roach-style trem).

[Bigyouth]

Thanks for the replies, and apologies for the late response..

So.. the way I picture it then; one wire from the output transformer (290v on the schematic) goes to the plate of the 12AX7 (pin 1).

The 1M resistor and 10n cap(s) connect to the grid (pin 2).

The 1k resistor that goes to ground, connects at the cathode, (pin 3).

The sine wave on the trem schematic goes to pin 3 of the pre-amp tube?

[tubeswell]

So.. the way I picture it then; one wire from the output transformer (290v on the schematic) goes to the plate of the 12AX7 (pin 1).

Don't think of the power supply (high tension) voltage for the LFO stage as being connected to the OT per se - Rather it has to be connected to the B+ (the OT primary just happens to have to be connected to the B+). And its the B+ side of the LFO's plate resistor that gets connected to the B+. The other side of the plate resistor gets connected to the LFO plate pin (either Pin 1 or Pin 6 in a 12A_7 dual triode, depending on which triode you wire the LFO stage up to).

The 1M resistor and 10n cap(s) connect to the grid (pin 2).

Yes the RC work of cap-resistor, cap-resistor, cap-resistor goes between the LFO stage's plate pin (say Pin 1) and the LFO stage's grid pin (would be Pin 2 in this case), with the 'free' side of each resistor going to the ground return (or, in the case of 1 of the 1M resistors - to the cathode (Pin 3 in this case)

The 1k resistor that goes to ground, connects at the cathode, (pin 3).

Yes the cathode resistor goes between the cathode pin (Pin 3 in this case) and the ground return

The sine wave on the trem schematic goes to pin 3 of the pre-amp tube?

Yes, the LFO's 'sine wave' (as you put it) indicates where the LFO signal is taken from (i.e. it is taken from the LFO stage's plate (Pin 1 in this case). This needs to be connected to the pre-amp stage's insertion point (say the cathode for bias wiggle) via a suitable high-voltage coupling cap. And you will also probably want some from of depth control of at least LFO signal strength attenuation between the coupling cap and the pre-amp signal insertion point (say one of the cathode's of a pre-am tube), in the form of a voltage divider or attenuation pot.

[hans-jörg]

Hi,

here, you can find some help, I guess:

https://tubeamparchive.com/viewtopic.php?t=13172

Hans-Jörg