72 bassman 100 mods

[Sometimesyoudie]

Hello all, this is my first post!

Just picked up a 72 bassman 100 head and 2x12 cab. I haven't spent alot of time with it but this thing has some incredibly sweet tone and huuuugggeee headroom!!

I got to dime it one time before the windows shattered and it was crunchy, vintage nirvana!

That being said, I will likely never get to dine this thing again as I imagine it would turn people's brains to mush. I'm going to do a recap job and I wanted to know who has had this exact head and who has modded it to have earlier breakup?

I know I can pull 2 power tubes but do I need to rebias?

Can I do a master volume mod to act like an attenuator and get the preamp section to cook at lower volume?

I know there are "blackface" conversions that are pretty simple but I want to do a conversion to get blackface tone AND sweet low volume breakup

It has a bass channel and a normal channel and I'm content with completely changing the bass channel as its pretty much useless for guitar stock

Also how do I know which bassman circuit I have? I googled and found eleventy-thousand different ones. This is the 1972 master volume silverface bassman 100 circuit

No I am not concerned with keeping this thing original or worried about resale value because this one isnt in immaculate cosmetic shape and it was pretty much given to me with the cab I bought.

Thanks for the input in advance!

[M Fowler]

Bass channel: How about some changes V1b cathode from 1k5 to 2k7, anode from 100k to 220k, slope resistor from 100k to 150k, bass cap from .1 to .047 and treble cap from .047 to .022.

Mark

[Sometimesyoudie]

Bass channel: How about some changes V1b cathode from 1k5 to 2k7, anode from 100k to 220k, slope resistor from 100k to 150k, bass cap from .1 to .047 and treble cap from .047 to .022.

Mark

That sounds easy enough, should I make any changes to the beget ive feedback loop? I've heard there are all kinds of uneccesary "extras" in these circuits to keep it cleaner and to compensate for poor soldering

[M Fowler]

I believe this your schematic.

[M Fowler]

Bass channel: How about some changes V1b cathode from 1k5 to 2k7, anode from 100k to 220k, slope resistor from 100k to 150k, bass cap from .1 to .047 and treble cap from .047 to .022.

Mark

That sounds easy enough, should I make any changes to the beget ive feedback loop? I've heard there are all kinds of uneccesary "extras" in these circuits to keep it cleaner and to compensate for poor soldering

Right now you have an 820r NFB resistor you could add a presence pot yank out one of the Bass channel input jacks and insert small pot for presence.

Mark