turning a 4x10 '59 Bassman RI into a 1x12?

[appar111]

I'm thinking of trying something a little crazy and converting my 4x10 BMRI into a 1x12. I know that I'd need to have a new baffle cut (I'd probably just order it from Weber so I could get it covered in oxblood grillcloth), and I'd have to decide on the right 12 inch speaker, but I had another question.

Right now, all 4 speakers connect to the chassis by way of 4 separate speaker inputs. How would I go about hooking the 1x12 up to the chassis? Is it ok to only use 1 of the 4 speaker inputs? And if so, what ohm rating would I need for the single 12" speaker?

I thought I'd go for a 1x12 because I played a Deluxe Reverb the other weekend and the single 12 in a bigger cabinet really sounded great, so I thought "man, that might make my bassman sound cool". And since I'm going for a more rock & roll vibe w/ my setup (lovepedals and the addition of a new SG), I thought a 12 would have a little more beef & body to it. That and it would make the amp lighter, which is always a plus :)

So does this sound like a bad idea?

[KC]

wellsir, I never heard a single 12" setup that had anywhere near the "beef & body" of a 4x10 rig. I've got a 1x12 Badcat extension cab which is pretty big and very solidly built but it doesn't move air like a Super Reverb. something about the surface area of the cones & the way the four speakers couple & jack up the low end when they're moving all at once -- I don't know, it's a thing of beauty.

[Steve McGinnis]

Originally Posted by appar111

Right now, all 4 speakers connect to the chassis by way of 4 separate speaker inputs.

Are you sure about that? Stock all 4 speakers are routed "Parallel" meaning you have one set of wires (one black one white) which connects to one speaker, and then the next speaker etc. You will have only one jack attaching to the chassis. The speaker impedance of all of them together is 2 Ohm, which you won't find in a 12 inch speaker.

Just curious, why do you want to do this anyway?

[appar111]

Originally Posted by Steve McGinnis

Are you sure about that? Stock all 4 speakers are routed "serial" meaning you have one set of wires (one black one white) which connects to one speaker, and then the next speaker etc. You will have only one jack attaching to the chassis. The speaker impedance of all of them together is 2 Ohm, which you won't find in a 12 inch speaker.

Just curious, why do you want to do this anyway?

Yes, I'm sure about that. There are definitely 4 jacks connecting the speakers to the chassis. It looks like each speaker has a brown and a black wire that are wired to an RCA type connector, and there are 4 of those connectors (1 for each speaker) on the amp's chassis.

As far as why I want to do it, did you read my post at all?

[refin]

My old '59 has 4 seperate speaker outs....all RCA.

[appar111]

Originally Posted by refin

My old '59 has 4 seperate speaker outs....all RCA.

What are the ohm ratings for your speakers?

I didn't mean to come off harsh to Steve, it's just that I know that this amp had 2 separate speaker outs. Maybe other versions of the Bassman have speakers routed in serial?

Anyhoo, I just need to know if I can use only 1 of the 4 speaker outs, and if so, what ohm rating for a single speaker.

[appar111]

Steve-
I checked Fender's specs for the current '59 Bassman Reissue (the lacquered one w/ the pine cabinet) and it does say 45 watts into 2 ohms, but my Bassman RI is one of the ones from the early to mid 90's, and mine is wired like Refin's with an RCA jack for each speaker.

So are the current BMRI's speakers connected to the chassis differently? (i.e. they don't use 4 RCA inputs; 1 for each speaker?)

[tele_player]

All 4x10" Bassmans (and Super Reverbs) use four 8 ohm speakers in parallel, for a 2 ohm load.

You can't get a 2 ohm speaker - so the correct way to run into a single speaker would be to get an 8 ohm output transformer and 8 ohm speaker, or a multi-output transformer, some are 2,4, 8, or 4, 8, 16.

A Twin Reverb output transformer could also be used. It's intended for four 6L6 into 4 ohms, which works out the same as two 6L6 into 8 ohms. This has been the choice for many who have done conversions from silverface Super Reverb into '64 Vibroverb, aka 'VibroClone'.

[Steve McGinnis]

Originally Posted by appar111

As far as why I want to do it, did you read my post at all?

Sorry about that, I actually thought I had read your post. I reread it and realized I had completely skipped the entire last paragraph. Brain fart...

I've played and seen alot of Bassmans and I had never looked underneath to see the 4 RCA setup. I thought the 2 ohm load was wired the same as my Super reverb. So another Whoops. Looks like I failed the TDPRI test...

I do suspect that it is still an amplifier designed for a 2 ohm output. 12" speakers come in 8 and 16 ohm without a special order. Weber speakers will make 4 ohm speakers, I don't know if they make 2 Ohm.

I used to have a 65 super reverb (also is a 2 Ohm out) that had been changed to have a 15" 8 ohm JBL and it worked fine, but according to the amp experts, that is a good way to cook an output transformer.

[Steve McGinnis]

Double post...removed

[mr_hankey]

I'm pretty sure Weber can sell you a 2 ohm speaker.

[Bill Hullett]

FWIW.....
I think the term that you guys are looking for is Series, not Serial.....But its a moot point because wiring (4) 8ohm speakers in series would produce some ultra high impedance that my brain can't figure out this early...the four speakers in a bassman are wired in parallel

The best way to "alter" the impedence issue would be to install a tapped output transformer that can be switched from 2-4-8 ohms as desired. the 4 rca plugs are all wired in parallel in the chassis of the bassman so it doesn't matter if one is plugged in or 4 are plugged in....the thing that matters is how many ohms load that the amp is seeing when your speakers (or speaker) are hooked up...

I don't think you'd be happy with the outcome either but thats JMHO...

I've never heard of a 2 ohm speaker.....

Bill Hullett

[Wally]

just a thought.....'rock and roll' vibe....
the 5F6A Bassman is one of the best rock guitar amps ever built. IT
is the basic format for the first Marshalls, and those amps made rock'n'roll history. There is a reason why Fender reissued the 5F6A....it rocks!
If you have to do it, Appar111, then imho changing the OT is the way to go.
A 15" Ev would make that circuit jump fatly, but the 4X10's push more air and probably cut better through a mix.

[Marky D.]

I once had a 59 bassman chassis I bought w/ no cab for $150.

I built an accurately sized cab for it and ran an Altec 417B in it for a while.. didn't sound very good - maybe because of the impedance mismatch.

The alnico 10s in a BMRI are pretty sweet - I was suprised when I plugged my 65 DR into the bassman's speakers. I'd keep em as is and focus on the electronics if you don't mind me saying.. Also, have you ever tried JJ 6v6s in that thang?

Good luck!

[appar111]

Yeah, perhaps I should just leave a good amp as a good amp, instead of trying to hot rod it. I just thought that since it was the blueprint for Marshall, why not try to put a 12" speaker in there? Or maybe 2x12.

I could always contact Ted and see if there's a possibility for a 2 ohm speaker. I would assume I'd just plug into 1 of the 4 RCA inputs on the chassis.

EDIT:
I just checked Ted's website and it looks like they do make a selection of speakers in 2 ohm versions. Now I just need to find out how much they would charge for a baffle w/ oxblood grillcloth.

The great thing about this is that if I decide to go back to stock, all I have to do is put the original baffle & speakers back into the cab.

[KC]

well, you could try cutting a new baffle & dropping in a pair of 4 ohm 12s, you'd still be moving a lot more air than a 1x12, little different dynamics than a 4x10, could be interesting. say a weber ceramic blue dog & a ceramic silver bell. could be pretty cool.

[appar111]

Originally Posted by KC

well, you could try cutting a new baffle & dropping in a pair of 4 ohm 12s, you'd still be moving a lot more air than a 1x12, little different dynamics than a 4x10, could be interesting. say a weber ceramic blue dog & a ceramic silver bell. could be pretty cool.

Especially w/ a dirt pedal in front of it.

I also read that Santana uses 4x12 cabinets but only has a center loaded 1x12 in it. After hearing how a larger cabinet for a 1x12 speaker sounds, I really like the change in tone.

Heck, I could go for a 15" speaker instead of a 1x12 or 2x12--- sort of a Bassman "Delta Blues" of sorts.

[appar111]

Originally Posted by Marky D.

I once had a 59 bassman chassis I bought w/ no cab for $150.

I built an accurately sized cab for it and ran an Altec 417B in it for a while.. didn't sound very good - maybe because of the impedance mismatch.

The alnico 10s in a BMRI are pretty sweet - I was suprised when I plugged my 65 DR into the bassman's speakers. I'd keep em as is and focus on the electronics if you don't mind me saying.. Also, have you ever tried JJ 6v6s in that thang?

Good luck!

What would be involved in converting it from 6L6 to 6V6's? I actually really like the 6L6 sound, but I also like the sound of 12" speakers, there's less projection than with 10's, a little bigger sounding.

[Marky D.]

You'd have to re-bias.. I have a Hoffman board in mine so it's not too difficult. I think I had to adjust the bias range resistor. The JJ's appear to be robust enough to take it. I have it set up w/ a 5U4 rectifier. I used it at a loud jam a few weeks ago and it did well w/ both channels half way up. Gets crunchy in a hurry & not so LOUD around the house. The tone is noticeably sweeter, which I didn't expect.

I understand what you want to do w/ the single 12. I spose if you could find a "Bassbreaker" and it would be similar. Interesting about the Santana rig...

[appar111]

I think I'd probably stick w/ the 6L6's then.

Now I just need to find a 12" or 15" speaker that will sound nice in the bassman. Weber has a ton of options in the 50 watt range at 2 ohms. I may pop over to those forums and see what the recommendations are..