Removing Negative Feedback

[maxkracht]

leave the resistor, unsolder the other end of the wire connecting to the speaker, attach that to your switch then run another wire from the switch to the speaker jack.

[zozoe]

The end of the resistor is connected to that Green wire which goes into the tranny, with ANOTHER Green wire emerging from the tranny & going to the speaker....
So, lifting that R38 as it sits (the tan side of board) on either end, won't remove the NFB?

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[maxkracht]

Lifting the resistor will do the same thing, just less chance of damaging the board if you don't touch the board. It either takes NFB from another transformer tap or two leads coming off of the same tap. You can remove the green wire from the board and add a switch between it and that resistor, or lift the resistor.

[zozoe]

Thnx Max,,, so take this green wire, & insert my double throw on/off switch there,, Green wire to one pole, & a wire from that (former) connection to the other pole.... then I can chassis mount somewhere on the back? Again, that Green wire goes into te tranny,, No issue, right? the only destination and end of the line for the nfb R is that Green wire, I assume?
Thnx, Kenny ॐ

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[maxkracht]

Yes, if there is enough extra length on that green wire you could just cut it in half and connect the two halves to a switch. If there's a ground switch that's no longer being used you might be able to use that and avoid drilling extra holes.

[zozoe]

And THAT Green wire doesn't go directly to the speaker lead,,, it goes into the tranny first.... I'm good there?
thnx a mill~ॐ

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[maxkracht]

Yes. Closeups of wires aren't giving me any information, but if that resistor matches the schematic and there is a wire coming from the transformer it should be the NFB tap.

[zozoe]

Well folks, all in all, faster than it takes to change all 6 strings on a gtr., it's done!!
I live it when everything simply falls into place..... thanks again!!
and it sounds AWESOME ÷÷

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[wpaulvogel]

And THAT Green wire doesn't go directly to the speaker lead,,, it goes into the tranny first.... I'm good there?
thnx a mill~ॐ
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Apparently when the transformers were ordered Ampeg specified an internal tap for the NFB which kept the wires closer to the board. It’s actually a good idea in this case because the wire passes through the chassis and solders close on the board. NFB wiring can cause parasitic oscillations if the routing is clumsy and this is neatly done.
How do you like the amp without the NFB.