Got me a little '83 Bassman 20 combo with a closed 15. It sounds ok, but not great. Tubes have been replaced at least once, i think, but prob not in a while. Innards haven't been replaced as far as I can tell, and the board is sagging bad. Besides maybe swapping out some tubes and a cap/resistor or two, can anyone suggest any improvements? PM for schematic, or if you've got the Tube Amp Book its on the CD (read: the useful part of the book).
I've looked everywhere on the internet, and its such a rare (rare but not at ALL collectable, gotta love that) amp that no one really talks about it.
I'm open to any suggestion, just make sure you tell me what it'll do because I'm new to this.
Ben
Modding a Bassman 20
Moderators: pompeiisneaks, Colossal
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oldhousescott
- Posts: 94
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- Location: South Carolina
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Re: Modding a Bassman 20
Well, if the electrolytics haven't ever been replaced, they're due. Is there some problem with the amp you're trying to fix, or is it a tone thing? Just trying to get a feel for what you're wanting to hear.
"We put a little quality in everything we build..."
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Re: Modding a Bassman 20
Just a tone thing. Plus I'd like to be able to get a little dirty out of it, but I don't know what I want realy, just a pretty clean sound is the best I can tell you. I should replace the electrolytics though.
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oldhousescott
- Posts: 94
- Joined: Sat Apr 15, 2006 3:18 am
- Location: South Carolina
- Contact:
Re: Modding a Bassman 20
Well, from the input to the PI through the output stage looks fine. It looks like they tried to knock down the gain a good bit around the second stage (the makeup stage after the tonestack).
Moving from the input toward the PI, here's what I would do:
-- Replace the .001 cap across the 820k resistor after the treble pot with a jumper
-- If this amp is for bass use, remove the 100pF bright cap on the volume pot
-- Change the 47k plate resistor to 100k
-- Replace the 22k resistor between the PI input and ground with 100k or higher, or just remove it altogether.
-- Replace the 1k / 1W resistor in the power supply rail with a choke (this would involve drilling a few holes in the chassis. Don't know if you want to go that far or not)
You probably won't get much more overall volume with these mods, but it should break up a lot sooner and give you a good bit of crunch at the higher settings.
Moving from the input toward the PI, here's what I would do:
-- Replace the .001 cap across the 820k resistor after the treble pot with a jumper
-- If this amp is for bass use, remove the 100pF bright cap on the volume pot
-- Change the 47k plate resistor to 100k
-- Replace the 22k resistor between the PI input and ground with 100k or higher, or just remove it altogether.
-- Replace the 1k / 1W resistor in the power supply rail with a choke (this would involve drilling a few holes in the chassis. Don't know if you want to go that far or not)
You probably won't get much more overall volume with these mods, but it should break up a lot sooner and give you a good bit of crunch at the higher settings.
"We put a little quality in everything we build..."
<><
<><
Re: Modding a Bassman 20
Thanks for the input, but I think the biggest problem I have right now is the 15 inch speaker. I can get it to break up some if I put a fuzz or a booster in front of it but its still not very nice/pleasant, more floppy and gross. I want to try the stock amp through a 2x12 or similar. I'll try the mods and see what I think though, when I get a chance.