Marshall silver jubilee half power switch removed.

[ericlen838]

I am building a Marshall silver jubilee 50/25 watt model 2550.  I do not want the half power switch and need some help.  To wire it for the full 50 watts I was going to tie down the 1k5 resister from pin 4 to pin 6 the link the 6 pins together.  Then the b+ to one of the 6 pins of the power tubes. Does that sound right?

[plexi50]

Yes but a pic just to be sure i understand your pin 6 screen resistor sides. I thought the 2550 used 1K screen resistors?

[ericlen838]

You would be right.  I was kind of using the Ceritone layout because this is my first build.  I checked the schematic against their layout and I only found a few difference I missed that one.  They also use a 5 k presence pot where the marshal schematic uses a 22k.  How would that affect the over all tone.

[HotBluePlates]

They also use a 5 k presence pot where the marshal schematic uses a 22k.  How would that affect the over all tone.

An older Marshall might use the 5k pot. The 2550 has a 4.7k resistor in parallel with the pot, so there's little difference.

The change in the 2550 was to re-arrange the presence cirucit a little to keep d.c. off the pot so it doesn't make a scratchy noise when adjusted.

If you're building a 2550, just copy the components and connections from the 2550, with the exception of the power switch as you noted. For what it's worth, that power switch is a pentode/triode switch, which some folks add on to their amps as a modification.