B+ and Filtering for Marshall Mod

[FourT6and2]

Marshall 1959T Super Tremolo. Schematic: https://schematicheaven.net/marshallamp ... _1959t.pdf

Let's say you were replacing the trem circuit with another 1-2 gain stages and cascading everything, for 4-5 total stages. Single gain control, single master volume. Pretty simple.

1. Would you add additional filtering for those first couple of stages? Otherwise, they all sharing 50uF.
1b. If yes, would you simply add another cap in parallel to bump up the total shared filtering OR would you add an additional 10K resistor (as an example) to isolate the first two stages? This might drop B+ and plate voltage too much though.

2. Where would you tap the B+ rail for this new tube? The stock 1959T has the extra tube for the trem circuit tapped between the PI and CF. But what about tapping B+ at the top of the two 100K plates for (old/original) V1?

[Roe]

1b yes add cap and dropping resistors. adjust value/voltage to taste

[FourT6and2]

1b yes add cap and dropping resistors. adjust value/voltage to taste

I suppose that means I should tap the B+ back up at the PI node then, to start with a higher voltage?

[Bergheim]

No problem with tapping the new preamp node off of the PI node for example. That way you retain a higher supply voltage compared to daisy chaining it onto the existing preamp node.

Edit:

1b yes add cap and dropping resistors. adjust value/voltage to taste

I suppose that means I should tap the B+ back
up at the PI node then, to start with a higher voltage?

You got there before me

[FourT6and2]

No problem with tapping the new preamp node off of the PI node for example. That way you retain a higher supply voltage compared to daisy chaining it onto the existing preamp node.

Edit:

1b yes add cap and dropping resistors. adjust value/voltage to taste

I suppose that means I should tap the B+ back
up at the PI node then, to start with a higher voltage?

You got there before me

Thanks for the confirmation though!

The previous version of this circuit I worked on had the B+ for the extra stages tapped at V1, before the 100K plates. And it sounded pretty good. I'm going to try it that way first because I already have it wired up for that. But I can always change it later. It's just moving one wire I suppose. Then adding a cap from that B+ node to ground for some filtering. And then I can add a dropping resistor to decouple. Here's a photo of the progress so far:

IMG_8244.jpg

Here's the amp stock, before I started the work:

IMG_8193.jpeg

[Roe]

1b yes add cap and dropping resistors. adjust value/voltage to taste

I suppose that means I should tap the B+ back up at the PI node then, to start with a higher voltage?

Or just connect the nodes in series. The preamp does not draw much corrent. a triode is around 1ma but the cathode follower draws around 3ma

[FourT6and2]

1b yes add cap and dropping resistors. adjust value/voltage to taste

I suppose that means I should tap the B+ back up at the PI node then, to start with a higher voltage?

Or just connect the nodes in series. The preamp does not draw much corrent. a triode is around 1ma but the cathode follower draws around 3ma

Yeah I've left it the way it was—like example A in the photo below. Example B is the other option I was thinking about (plus an added dropping/decoupling resistor not shown).

I fired up the amp last night and it seems to work haha. A little noisy, but nothing out of the ordinary for a typical '70s Marshall, which is actually pretty great considering this one has FIVE gain stages now haha. If I really wanted it perfect, I'd rewire the grounding a bit. But for now it's fine.

Voltages:

Plates: 512v
Screen drop: 5v
Before first 10K dropper: 510v
After first 10K dropper (half of 20K total): 430v
After second 10K dropper (half of 20K total): 352v (PI node)
PI plates: 230v / 247v
CF: 298v
Old V1 node (now V2): 273v
New V1 node: 273v
V1a plate: 210v
.

Filtering and B Plus.jpg

IMG_8261.jpg