Adding a tube tremolo to M15Mk1

Tio Pepe

Hi to all... Here is another cool idea to mod this great amp.

I've checked some early Marshall 18W schem, and I've understand that the tube tremolo circuit is pretty simple... it use one 12AX7, some caps and resistors. It come without switch, but with 2 inputs (High and Low) for normal channel and other 2 inputs for the tremolo channel.
The output of trem channel is goes to the other grid of PI, that normally is wired with a cap and this last goes to ground...
Now, I want to use this circuit with a DPDT, to switch thru a normal and tremolo channel, and where I need to wire the output of trem channel?
(sorry for this bad english :-[ )

futurama

Re: Adding a tube tremolo to M15Mk1

Why so complicated ?

Basically, the only thing you need for a tremolo is a low-frequency
oscillator and a LED/LDR-pair. No need to provide an extra channel.
The oscillator can be tube-driven or (more economic) a Timer-IC.

Do you need a tremolo, a third channel or an additional tube ?

wr, futurama

d95err

Re: Adding a tube tremolo to M15Mk1

Zitat von futurama

Why so complicated ?
Basically, the only thing you need for a tremolo is a low-frequency
oscillator and a LED/LDR-pair. No need to provide an extra channel.
The oscillator can be tube-driven or (more economic) a Timer-IC.
Do you need a tremolo, a third channel or an additional tube ?

The 18W tremolo is very different from a simple LED/LDR tremolo. It works by modifying the bias of the first preamp stage in a rather complex way. It will modulate, not just the amplitude of the signal, but also gain, headroom and frequency response. Even the depth control of this tremolo is interactive, since it changes the cathode resistor of the first gain stage. So even when it's off, it affects the sound.

Some say that it is the best sounding tremolo out there...

But, for a really simple tremolo, the easiest solution is a solid state oscillator and an LED/LDR, perhaps driven by the unused 20V tap on the PT.

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