Tube Amp Archive

Ahhhhhh, I see, the 13k3 and the 4k7 make up the 18k when NFB loop is at a minimum.....I'm learning Martin..... and maybe the drop off in volume is where the NFB loop is turning off, like JAZZ said..... I think I've made sense out of it. So really all i need to do is interrupt the wire leading from ...

Well, great news, switching the wires worked !!!! and with out having to rewire the speaker leads, I guess they were unaffected. I still have some questions though. When I turn the pot clock wise, to its lowest ohm reading, there's a tiny bite of travel right near the end where the volume will reduc...

Sounds good, I'll give it a try when I get home this evening. Thanks everyone

Just to ensure you're reading it right, be sure you're switching the PRIMARIES and not the SECONDARIES. It's always a crapshoot for me wiring in an OT with NFB. I do tend to be lucky more often than not and get it the first time, but basically, if you have them in backwards, you get positive feedba...

JAZZ, you may be on to something, after doing some preliminary reading on this, ....the blue and brown wires correct impedance are not relevant UNLESS you have a NFB loop applied (so says the internet)........will I have to do anything with my speaker wiring configuration after switching OT secondar...

What exactly does swapping these wires do..... like, does it do anything to the sound of the amp or change the tone in any fashion ? What would the amp sound like in stock form with these wires swapped ? Any how, I suppose you unsolder them from the power tube pins and switch them ? Thanks for the h...

Well, I wired it up like the drawing....the sound effect of the NFB loop was there still and seemed the same (good). One thing I noticed was the pot wiper noise was gone, it used to have a low audible hiss in all movement .....thats gone. I wired the pot to where full counter clock wise was 250k. Fr...

Man! That is awesome Martin !! Saved me alot of time !Thanks I'll report back

I think I would reduce the size of the tail resistor by ~5k, then connect the 0.1 cap to the bottom of that new Rtail, and then put a ~5k to ground. That will keep the total resistance from the PI cathodes to ground as it was, and fixed. Then connect a lead to a pot and a series resistor (say a 250...

Have you tried reversing the BRN and BLU wires of the OT primary winding? If the transformer is phased Brown to Yellow, then you are actually applying positive feedback, with will cause the amp to squeal. One way to tell if you've got the NFB phase right, is to compare the volume level with and wit...

I lifted the negative side of C25 cap and the tail resistor off of the pc board and connected them along with the NFB loop on one side of a 5k pot and then, to ground through a 250 resistor.

The amp is a little lower in volume with loop connected, from the factory, my speakers are 8 ohms each in series, a high FB resistor value makes the squeal stop......I have the loop connected at the tip terminal of the speaker jack

Ok guys glad I found this forum, decided to try a NFB loop on my Fender Prosonic combo, I'm not an expert on this but I'm decent. I've hooked it up a couple of different ways and it really makes the amp sound good but I'm flying by the seat of my pants and need to know a "correct" way to do it. Valu...