Issue with tremolo, "ploc" when switching.

[TriodeLuvr]

I just have to balance the level between tremolo on and off.

I wasn't aware of the 1930 circuit until you mentioned it (found it on the Tube Store Website). Could the on/off balance be the purpose of the additional pot at the cathode? That pot will set the DC idle voltage at the anode of the oscillator tube, which in turn modifies the gain of the preamp stage. If you have owned or used a 1930, you probably know whether that's its purpose. I'm no expert on tremolo circuits, so I could be wrong about this.

[PhilippeCamus]

I just have to balance the level between tremolo on and off.

I wasn't aware of the 1930 circuit until you mentioned it (found it on the Tube Store Website). Could the on/off balance be the purpose of the additional pot at the cathode? That pot will set the DC idle voltage at the anode of the oscillator tube, which in turn modifies the gain of the preamp stage. If you have owned or used a 1930, you probably know whether that's its purpose. I'm no expert on tremolo circuits, so I could be wrong about this.

I would say, yes and no. As the cathode are common, it has an action on the first triode, but this is not the purpose of this pot (the 5k). I don't know in English, in French we say "résistance talon", I would translate by position resistor.
With the switch modification the oscilator signal is much stronger. Too strong (bad sound after 8 on the intensity pot). This pot is for tweaking the max intensity. The 480 is also important.
To balance the 2 triodes I change the 220k or the 100k, I don't remember.
(Sorry, it's dificult for me to speak English this morning )

[TriodeLuvr]

Your English is fine. Certainly better than my French. Yes, I understand. Maybe the 100K resistor between the two anodes can be used to trim the gain when tremolo is off. There isn't much else in the circuit.

[Bieworm]

I'm confused that all that tweaking is necessary. The schematic as is has been built for decades... it's almost certain a layout problem. I'd be digging into that instead of adding more components...
A good and deep tremolo is going to make some noise to a modest level.. understanding exactly what it does to your signal...

[PhilippeCamus]

I'm confused that all that tweaking is necessary. The schematic as is has been built for decades... it's almost certain a layout problem. I'd be digging into that instead of adding more components...
A good and deep tremolo is going to make some noise to a modest level.. understanding exactly what it does to your signal...

I don't know. There are no error compare to schematic. The tube voltages are good. Tube, resistors, capacitors are good (measured with kelvin precision LCR and my tube meter). The only problem is the messy wiring. In fact, the tremolo is very unstable with HF feedback and motor boating. This amplifier belong to my guitar teacher and he don't want to spend money to rewire the amplifier (and I also don't want to waste too much time for free, even for my venerated teacher). The 1930 popular Marshall schematic mod works fine for a small amount of work. I agree with you, and I'm not very happy with this solution, but it works. My teacher is a stage professional musicien, and actualy with the covid he is economically weak. Maybe for the furure I will redo it for him.