Disconnecting tremolo tube with a switch--good or bad idea?

Leonc

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I'm considering building an amp that was designed with a tremolo circuit (Martin 112T); I've been told the tremolo sounds GREAT but that when you don't want trem, the amp performs a lot better when you just pull the tube (V6).

martin_112t_schematic.jpg


It appears that the only connections this tube has to the other circuitry (other than the filaments) is the lead from the depth pot to the bias on V1 cathode (pin 8) and the B+ coming off the 15uF filter cap.

I'm thinking of putting in a DPDT switch to disconnect both these connections. Seems like this would essentially remove the tube from the circuit. If this seems like a bad idea--I may be missing something really obvious--I'd like to hear about it.
 

phsyconoodler

Member
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4,301
A simpler way is use a switch to lift the ground on the depth control.That will do exactly what you want.It prevents the circuit from completing and shuts the tube down.

Actually in your case,the schematic shows a ground connection on the rate pot.It should be there instead.
 

Leonc

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Ah, so I'd really only need a on/off switch that way. Cool.

Unrelated question...do you have any thoughts on whether or not the B+ coming in via the 2.2M resistor connects to the .022uF cap that goes to pin 1 and pin 7? I really don't think it does...because that would mean it's going to both the plate and grid on the first triode...it's just that the way it's drawn, it almost looks like there's a connection.
 

phsyconoodler

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4,301
There is no connection there to B+. The coupling caps block the DC.
the cathode and grid are not joined,their respective resistors simply share a ground.The three caps are the time-tested timing caps to make the oscillator oscillate.You will find those three caps in almost every oscillator trem circuit.
Thje B+ at pin 1 does not go past those caps to the grid or cathode.
 

Leonc

Wild Gear Herder
Platinum Supporting Member
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Yeah, I noticed it looked very close to the 6G11 tremolo and other Fender trem circuits I've seen. So the 2.2M resistor (with B+) is just connected to the second .01uF cap, coming off the grid?
 

phsyconoodler

Member
Messages
4,301
Yes,the grid does not see B+ voltage.

The difference is the use of a varistor like Magnatone.Similar but different.That looks like a cool tremolo circuit!
 




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