variable NFB

I am looking at maybe installing a variable NFB in a 135 twin but have some questions, would a 25k pot be to much? also the 135 twin has 3 wires coming to the output (1- black, 1-green, 1 yellow/green). the y/g goes to the 820k with a white wire from the extension speaker jack would you lift both wires from the 820k and install the 25k pot or ?, also I have read that the effect maybe very subtle because of the ppmv, thanks in advance

http://c4.ac-images.myspacecdn.com/i...124a85977f.jpg

http://c1.ac-images.myspacecdn.com/i...db2b9e02ac.jpg

I put one (1 megohm) in my 66 ampeg and it makes a huge difference.

I disconnected it my '73 super and the difference was very unimpressive / not an improvement. I reconnected and left it alone

I disconnected the NFB in my pro Jr and left it, I prefer it

you could try disconnecting it and see if you like it, the pot adds some versatility - if you like the change

so they are taking the nfb off the 8ohm tap?

If I understand the diagram correctly the UL 135 amps use the nfb for the "boost". Like, when you pull the master vol knob for boost, you're hearing the amp with no nfb. Doesn't sound great IMHO.

BTW this reminds me of some tone stack mods I did to mine. I'm going to resurrect my thread on that if I can remember what I ended up going with.

OK that's not right. The nfb does go straight to the PI. Looks like it comes from the ext 4 ohm output.