I'm thinking about trying to make a modified Sunn Coliseum PA (just a schematic for fun for now) so that I don't have to pay 1.5-2.5k to get my hands on one, and so that it would fit my playing style/tone preferences.
I would cut out two of the 4 channels, have one with higher gain and one that's basically unmodified that has a normal gain level. I would make jumping these channels possible. I would possibly add a switchable tube boost circuit and a negative feedback control pot to the modified channel. Maybe a mid boost if I can figure out how to make one.
The real modification would occur in the power section. I want to remove two of the KT88 tubes, so it would be just a 2 tube push-pull section. Maybe I'd consider doing a class A KT88 build, but I think that the tone would be drastically altered, so I'll probably save that for a modified Deluxe or Princeton build and try to get 15 watts out of it. The push-pull dual KT88 setup is very similar to smaller Sunns of the time, which were good for 40-75 watts with two KT88/6550s. Still deafeningly loud, but I can at least attenuate it, as opposed to the mighty roar of 4 KT88s in the Coliseum. I think the only way to deal with that kind of power is to get an OX Box, and I'm not paying 2k for one of those. I'm planning on just dumping a Sunn Sentura or Sceptre power section in there and calling it a day.
My question is this: how will the proposed power amp modification affect tone? Given that one channel of the amp will be drastically changed from the original Sunn circuit, its not that important if its a little different, but I really want to get that sweet smooth Leslie West power tube distortion sound out of this amp. Would the sound be terribly different from a 4 tube setup?
I would cut out two of the 4 channels, have one with higher gain and one that's basically unmodified that has a normal gain level. I would make jumping these channels possible. I would possibly add a switchable tube boost circuit and a negative feedback control pot to the modified channel. Maybe a mid boost if I can figure out how to make one.
The real modification would occur in the power section. I want to remove two of the KT88 tubes, so it would be just a 2 tube push-pull section. Maybe I'd consider doing a class A KT88 build, but I think that the tone would be drastically altered, so I'll probably save that for a modified Deluxe or Princeton build and try to get 15 watts out of it. The push-pull dual KT88 setup is very similar to smaller Sunns of the time, which were good for 40-75 watts with two KT88/6550s. Still deafeningly loud, but I can at least attenuate it, as opposed to the mighty roar of 4 KT88s in the Coliseum. I think the only way to deal with that kind of power is to get an OX Box, and I'm not paying 2k for one of those. I'm planning on just dumping a Sunn Sentura or Sceptre power section in there and calling it a day.
My question is this: how will the proposed power amp modification affect tone? Given that one channel of the amp will be drastically changed from the original Sunn circuit, its not that important if its a little different, but I really want to get that sweet smooth Leslie West power tube distortion sound out of this amp. Would the sound be terribly different from a 4 tube setup?
