68 Bassman doesn't sound "right"

[glebert]

Whatever "right" is. I got a project 68 drip edge Bassman head in a trade. Bass channel wasn't working, turned out to be cracked solder joint on the heater wires for V1 tube. Got that fixed, but the amp just doesn't sound that great to me. Boomy bass and harsh highs on both channels. Appears to be an AB165, with some kind of mods. There are mid pots added to both channels, volume knobs moved over to the 2nd input jack holes. Some resistors not on the eyelet board, but an extra little board added next to V1. The balance bias adjustment seems like it was converted to a regular bias since the currents go up and down together.

I've tried different output tubes, going from the cheap Sovtek coin base 5881 it came with to Svetlana 6L6 helped some, but only a little. I guess I could try a different V3 and V4 tubes? Wondering if I should rip out the mid pots and just put it back to stock. Wiring in general seems pretty good as far as workmanship and attention to detail.

Thoughts?

[Leo_Gnardo]

Whatever "right" is. - - - Wondering if I should rip out the mid pots and just put it back to stock.

If you want "right" then yes, rip out mods and return to stock. With one possible exception, the mid pots. Heck I've added mid pots to hundreds of Fenders, in most cases using the input 2 jack but so what if the modder used input 1. All the mid pot does is substitute a pot for the fixed resistor in the tone stack, 6K8 in the norm chan and 8K2 in the bass chan. So - a 10K pot is fine, bump it up to 25K if you want to dial up plenty of midrange honk. With the mid pots set at the point they match the original stock resistors you can expect your prize to sound "right" - that is, if everything else in the amp is square up with the original circuit.

One thing we don't see in the photos is, did the modder swap in different value pots for treble, bass, volume? We don't really need another photo, just have a look for yourself. If you choose the return-to-stock path, do make sure the pots are proper value & taper. Don't assume, check 'em individually and if they're not right put the right ones in.

[Jazz P Bass]

That bypass cap on V1 cathode will certainly pass all of the frequencies. (250uf !)

[Leo_Gnardo]

That bypass cap on V1 cathode will certainly pass all of the frequencies. (250uf !)

We see those on tweed bassman. Bit of an over reach innit? Bandwidth down to earthquake frequencies all right.

Similar 320 uF on JMP Marshall fat channel. We know where Ken Bran borrowed his ideas...

Some home builds I've seen sport 1000 uF caps there. "Cause, you know, ya get more bass that way.

[Helmholtz]

There shouldn't be an audible difference between 250µ and 25µ. It doesn't get flatter than flat.

I recommend to map the schematic from the amp as it is - without looking at the original one.

[vintagekiki]

Apparently someone was learning to make some project or mod. Just in case, ask the owner that it is not a Bassman with mod as a guitar amp.

If you want from a failed experiment, to make amp with "right" sound, only solution is to return the amp to the original schematic.
http://www.thevintagesound.com/ffg/bassman_bf.html

Mid pots as mod you can keep, use schematic from Bassman 135
http://www.thevintagesound.com/ffg/schem/bassman_135_schem.jpg

Relatively little work, to get a lot of sound.

[glebert]

Apparently someone was learning to make some project or mod. Just in case, ask the owner that it is not a Bassman with mod as a guitar amp.

I am the owner, but did not do the mod, neither did the guy I got it from. It was actually used by a band called The Peels out of Seattle at some point, probably for guitar. I reached out the guitar player from that (now defunct) band for info but never got a response. Reached out to a tech in Seattle who had put a sticker on the back but he had worked on it a long time ago and had no notes on it.

I think the "map out the circuit as it is" and then "return it mostly to stock" is probably the right approach, but doesn't fall into my preferred quick-and-easy category...

[nosaj]

[glebert]

I like that track. Looked but couldn't find any picture of them playing with the Bassman.

[drewl]

Sort of famous gear, eh?

I have a 70's Marshall 4x12 that had EZO stenciled on it.

Figured they were just a local band until I read the Slash autobiography.
They were a Japanese metal band that opened for GnR in NY.

[vintagekiki]

I think the "map out the circuit as it is" and then "return it mostly to stock" is probably the right approach, but doesn't fall into my preferred quick-and-easy category...

Bassman is Bassman.
If amp is in working condition, best is "let down through the water" (sale it)
Tastes are different, maybe someone will like the sound.

[glebert]

Bassman is Bassman.
If amp is in working condition, best is "let down through the water" (sale it)
Tastes are different, maybe someone will like the sound.

This is not bad advice. I don't have time to open up the amp right now to look at the pots but did try it through a different cabinet and the sound is much more "useable," but definitely more Marshall-y. First cab was a big blackface 2x12 Bassman with closed back and some random speakers that gives a pretty good Fender sound with AB763 circuits. Second cab is open back 2x12 with Jensen Mod speakers. Looking at recommendations for speakers to use with the a Bassman (for guitar) it seems everyone recommends something more in the Celestion vein than what Fender would have paired with it.

I also read that for Bassmans you really need to drive them to natural distortion to sound good with guitar, but I don't have an attenuator and that would be way too loud for in the house playing.

[nosaj]

This is not bad advice. I don't have time to open up the amp right now to look at the pots but did try it through a different cabinet and the sound is much more "useable," but definitely more Marshall-y. First cab was a big blackface 2x12 Bassman with closed back and some random speakers that gives a pretty good Fender sound with AB763 circuits. Second cab is open back 2x12 with Jensen Mod speakers. Looking at recommendations for speakers to use with the a Bassman (for guitar) it seems everyone recommends something more in the Celestion vein than what Fender would have paired with it.

I also read that for Bassmans you really need to drive them to natural distortion to sound good with guitar, but I don't have an attenuator and that would be way too loud for in the house playing.

Aww come on.....Let err rip!!!!

nosaj

[glebert]

Aww come on.....Let err rip!!!!

nosaj

My neighbor just listed their house, maybe I should wait till they are doing a showing, open up the windows, and let loose with some "Stranglehold."

[nosaj]

My neighbor just listed their house, maybe I should wait till they are doing a showing, open up the windows, and let loose with some "Stranglehold."

Or a Pay not to play agreement? Hey if you can't make money off your neighbors what are they there for?
nosaj