122 vs. 147 what do you think?

[DanielP]

Just out of curiosity is there the same difference between the 6L6 tube amps unbalanced vs balanced. i.e. a 32H amp = "spitty distortion" and 46w = loud, cleaner, less distorted?

It seems like it wouldn't be too difficult to mod the preamp stage in a 147 to get a more 122 sound. I've read about the preamp tube making quite a difference. The 12AX7 being a hotter tube giving a bit more distortion when cranked vs the 12AU7 which is less gainy. Maybe there is a even more gainy preamp tube option in place of the 12AX7 which could bump the 147 up a notch for some more 122 results? What about alternate 6550 tubes in the same family, are there other tubes which may make a 147 more gainy?

[Guitarbro]

The 122 and 147 amps have similar design but the 147 has negative feed back. This is why it breaks up at a higher volume and sounds more harsh.
schematics:
147
122

[goldnmold]

What is negative feed back exactly? Not sure where in the circuit this occurs, could a 147 be modified to do that while still taking the normal unbalanced signal? Thanks for the schematics, I notice that the circuits are different in a few pretty big ways, first being the extra 12au7 in the 122.. Only half is used though, is this tube used for switching or power supply? I'm not sure its in the audio path.. The other 12au7 is used differently in the two amps, I noticed that the 147 is 115v and 4.5v, while the 122 is @ 130v and 6v. The tube would be running hotter I suppose, I'm not good enough with the schem to see what's causing that though...

[Guitarbro]

The inverted output is fed back to the output tubes compensating for some distortion.
voltage differences have to do with the fact that the 147 has to amplify and create an inverted wave form while the 122 already has the inverted signal so only amplifies them.