Jose-ish mod to Bassman AB165 (draft schematic enclosed)

duncan

duncan

Active member
Howdy Rig Talk'ers

I've got a Fender Bassman AB165 (that has been rebuilt, so there's no vintage/sentimental value left), that I've been looking at turning into a firebreather (more or less a Jose mod to the normal channel) while keeping the Bass Instrument channel stock. I'd like to avoid drilling any new holes in the chassis (if possible), so I've added a FET follower to replace a CF that I've seen in many different schematics.

Anyone care to comment on this? I plan on using as many existing holes for potentiometers as possible (but if some have to go in the back, that's not the end of the world).
 

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1) there's a problem with the way you've drawn the plate supply and the bias supply.
2) what is the purpose of the 10k between the 2 haves of the plate supply can cap?
3) you have a fet gain stage before the fet follower. No idea whether this will work or not, but you don't need another gain stage here.
3 tube gain stages is plenty if you are going to add clipping as well.
4) you have 2 .001uf caps to ground in the preamp. The first one will likely be enough, or the amp will be too dark, and you could also try plate snubbing instead to get the desired result.

Your main areas of tweaking will likely be the above mentioned high end snubbing, the bright caps on the gain pots, and the resistors to ground on the interstage voltage dividers.
Keep this in mind as you lay out your mod, as you will likely be doing some repeated component swapping in thes areas.

Good luck with your project 👍
 
Might want to switch your first two couplers around. You have a 0.0022uF first and then 0.022uF. Kind of pointless since the first coupler will filter out all the bass that the second one would otherwise let through. You can try it either way, but in my experience it sounds better with the larger one first. Up to you.
 
I'd probably use the Bass channel for the mod and leave the Normal channel mostly stock (eliminate that shared third stage leaving it like a Fender guitar preamp). Then you'll have 2 full preamp tubes (4 triodes) to work with. It will also put the higher gain channel further to the 'quiet' end of the chassis. But you have to get creative with the knobs no matter what you do. IMO, if you're taking it that far go ahead and drill a hole or two.

EDIT: and I'd probably just go for the 'regular' Jose (without the extra gain stage). I always tend to prefer that over the one with the added gain stage but I've only played/built and handful. And even then I don't use any clippers. The extra gain stage AND clippers is way too much for me.
 
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Yeah I would choose one or the other as well. Either 4 stages OR 3 stages + diodes. Unless you're gonna make the 4th stage switchable. But I suppose 4 stages with the gain run really low + diodes will sound good and different enough from just 4 stages with the gain cranked.
 
Totally unrelated but I had the opportunity years ago to get a kruse modded bassman head for like $600…. And it was local which is what is shocking. I heard they are awesome….
Damn…not sure if it was a kruse or not…some guy that did pretty good vh mods….
 
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I'd use the solid state gain stages at the front instead of at the end. You seem to be missing a tube stage too? Use an LND150 for the first stage and tube for the rest.
Also 4 gain stages + diodes is usually too much. I recommend dropping a gain stage or drop the diodes. Edit: as others have said above
 
SpiderWars said:
I'd probably use the Bass channel for the mod and leave the Normal channel mostly stock (eliminate that shared third stage leaving it like a Fender guitar preamp). Then you'll have 2 full preamp tubes (4 triodes) to work with. It will also put the higher gain channel further to the 'quiet' end of the chassis. But you have to get creative with the knobs no matter what you do. IMO, if you're taking it that far go ahead and drill a hole or two.

EDIT: and I'd probably just go for the 'regular' Jose (without the extra gain stage). I always tend to prefer that over the one with the added gain stage but I've only played/built and handful. And even then I don't use any clippers. The extra gain stage AND clippers is way too much for me.
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Ha well the thing is, I want to be able to continue using it as a bass amp (in the rare occasions where I have to play bass), so ideally, I'd leave the bass channel alone.
 
duncan said:
Ha well the thing is, I want to be able to continue using it as a bass amp (in the rare occasions where I have to play bass), so ideally, I'd leave the bass channel alone.
Click to expand...
I didn’t think that Bass channel was good for anything including Bass but I don’t really play bass. So in your case yeah that explains it.
 
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