Vintage cab experts needed! Looking at a 70's cab with Greenbacks

[soundboy57]

I meant to say Grey, not cream end of '72, but George is the guy, right down to the month. Thanks for sharing all of that

 

[george76]

Well was there any mueller coned greenbacks?? I was thinking the change to the lighter grey cones w no doping around dustcap was after the magnet cover color change. Is this right?? Soundboy George?

No Mueller coned greenbacks. The earliest I have seen them is 75. Last of the creambacks.

There might be some around from 74 but I have not seen any myself.

 

[BWOTW]

It's mine!!!

I've checked the speakers, I'll post pictures later. Two are stamped '1777', one '3' and one I can't quite see, being at the bottom, though I'm guessing it's a '3' too, so it checks out for a '73. It's been rewired back to mono, but I'm unsure how and what Ohms are required. I'll post pictures with the wiring to see if you guys can help me.

For the moment, I'm using the 4Ohm out in my 2203, just to be safe. So far, I like it more than the V30's, I can tell you that Way more natural and sweeter sounding top, it's difficult to make it sound harsh (and, yes, lower volume too, as expected!). Not as big sounding, but clearer, I like that!

I need to do something with the cloth though, since the loose threads from the grill rattle at moderate volume. But so far so good!

 

[tweedman8758]

Congrats! That's got to sound really sweet with the BJA!

 

[stalefish]

I'm unsure how and what Ohms are required.

Um, man figure that shit out before you hurt that wonderful head you have sitting on top of it.

 

[BWOTW]

Congrats! That's got to sound really sweet with the BJA!

Indeed it does! And even better with the SG (w/ Duncan Antiquities)

Um, man figure that shit out before you hurt that wonderful head you have sitting on top of it.

I figured it wouldn't be less than 4 Ohms anyway, so I think it's OK! Here's the code on one of the speakers, excuse the crappy cellphone pics:

The whole back:

Can you tell me what kind of wiring is this? And what Ohms should it produce? I've checked out schematics but still can't figure it out, electronics are defintely one of my weaknesses

Upper left speaker

Upper right speaker

Lower left speaker

Lower right speaker

Jack:

 

[stalefish]

I'm thinking it's 16 ohms. It can only be 16 or 4 with those speakers.

Do this...plug a cable into the cab jack. Use a multimeter set to Ohms and connect one lead to the tip of the cable, and the other to the sleeve. It's going to read around 16, or 4.

 

[BWOTW]

I'm thinking it's 16 ohms. It can only be 16 or 4 with those speakers.

Do this...plug a cable into the cab jack. Use a multimeter set to Ohms and connect one lead to the tip of the cable, and the other to the sleeve. It's going to read around 16, or 4.

I didn't even know it could be measured like that, thanks! I'll try to borrow a multimeter and get a reading.

 

[stalefish]

Yep, and while you're in there, just for kicks, make sure the speakers are wired in phase. This is also a simple test. You know about the tip and sleeve now right? So take those same multimeter leads connected to the tip and sleeve of the speaker cable, and touch them to a 9 volt battery. The speakers should all jump in unison and in the same direction.

 

[george76]

It looks like the wiring is back to stock so should be a 16 Ohm cab.

It is the standard series/parallel wiring, just looks complicated because of the twisted wire. Double check they are soldered to the correct terminals.

 

[tweedman8758]

Indeed it does! And even better with the SG (w/ Duncan Antiquities)

You might like the BJA more once you get a real P-90 and a PIO cap in it. Just my
I love my real PAFs. Ain't nothing sweeter, but damn a P-90 can get your blood chuggin'

 

[george76]

Just looking at your jack socket, it could be wired up incorrectly. When the wiring is blue and brown, the brown is positive. So that means the brown should be at the tip of the jack socket, not the blue...

 

[BWOTW]

Just looking at your jack socket, it could be wired up incorrectly. When the wiring is blue and brown, the brown is positive. So that means the brown should be at the tip of the jack socket, not the blue...

Thanks for the observation, but I'm confused. Isn't the negative here on the tip and the positive on the sleeve?

Mine is just like the schematic. I've measured it, it's indeed 16ohm and all the speakers are in phase...

... but I think I'll rewire it to parallel 4 ohms anyway. Why? Because my JMP doesn't have a 16 Ohm out (it's one intended for the Scandinavian market, similar to the Canadian Marshalls).

For YEARS I was sure that a mismatch in impedance was no big deal if you went up (like I've always used, 8ohm out into 16 Ohm cabs). But I've learnt a lot reading this forum this past couple of days and I'll match impedances exactly for now on. Today I played low volume with it 8 into 16 and sounded great, but before I crank it confidently, I'll get the cab rewired.

Thanks to everyone here, you've been a great help!!!

 

[soundboy57]

The diagram is correct, but the arrows at the input jack are a bit confusing as to where they are pointing.

 

[Vanyu]

Instead of re-wiring your cabinet to 4 ohms, I'd STRONGLY urge you to just pull your outer two power tubes instead, for two reasons:

1. When you pull two power tubes, the impedance is also halved, so to run your 16 ohm cabinet, you set your amp to 8 ohms, which I believe is present on Scandinavian models

2. These amps kick out a helluva lot more than 100w under load. I've seen numbers as high as 210w with 6550 power tubes. You greatly reduce the risk of blowing up your cab by pulling a couple tubes

And also, NEVER mismatch impedance on a Marshall, something bad WILL happen. If you do decide to just pull two tubes, your impedance will be correct

 

[Gene Ballzz]

Yes Indeedy,
I'd be real careful about "CRANKING" that 2203 through that cab that is only rated at 100 watts! I'm kinda surprised that with all the well seasoned, knowledgeable folks who've replied here, that they all seem to have missed the "JMP 2203" part of your first post. It may be likely that they became so focused on the coolness of the cabinet that they inadvertently overlooked or missed that fact!

Either way, I've certainly seen a fair number of greenback cabs blown with a 100 watt head. Now, if you don't run your amp insanely flat out cranked into power tube overdrive/distortion, that's a different story, but where's the fun in that! I think you need a matching "B" cabinet to be safe and hey, then your impedance will correct wit two 16 ohm boxes!
Just Sayin'
Gene

 

[BWOTW]

Instead of re-wiring your cabinet to 4 ohms, I'd STRONGLY urge you to just pull your outer two power tubes instead, for two reasons:

1. When you pull two power tubes, the impedance is also halved, so to run your 16 ohm cabinet, you set your amp to 8 ohms, which I believe is present on Scandinavian models

2. These amps kick out a helluva lot more than 100w under load. I've seen numbers as high as 210w with 6550 power tubes. You greatly reduce the risk of blowing up your amp by pulling a couple tubes

And also, NEVER mismatch impedance on a Marshall, something bad WILL happen. If you do decide to just pull two tubes, your impedance will be correct

Yes Indeedy,
I'd be real careful about "CRANKING" that 2203 through that cab that is only rated at 100 watts! I'm kinda surprised that with all the well seasoned, knowledgeable folks who've replied here, that they all seem to have missed the "JMP 2203" part of your first post. It may be likely that they became so focused on the coolness of the cabinet that they inadvertently overlooked or missed that fact!

Either way, I've certainly seen a fair number of greenback cabs blown with a 100 watt head. Now, if you don't run your amp insanely flat out cranked into power tube overdrive/distortion, that's a different story, but where's the fun in that! I think you need a matching "B" cabinet to be safe and hey, then your impedance will correct wit two 16 ohm boxes!
Just Sayin'
Gene

Thanks guys! That's defintely another idea to ponder. I might have not explained myself very well when I said "crank it up" I still rely mostly on preamp distortion, right now I'm only playing on 2 on the volume knob but, at the very, very most, I'd be going up to 5 or so. Would I be still at risk of throwing more than 100w into the cab?

 

[george76]

Thanks for the observation, but I'm confused. Isn't the negative here on the tip and the positive on the sleeve?

yeah bad diagram in that respect. (it was done by jim scumback afterall ). i guess the circuit is just in reverse now on your cab, thats why it still works.

basically the tip of the jack (the pointy bit) is positive:

behind the black ring is the negative part.

so when you wire the socket, the part that connects with the tip is where you should solder the positive wire. usually the furthest part from the 'entrance' of the socket on a cliff jack. on a switchcraft jack you should solder to the larger piece of metal that touches the tip of the jack:

 

[Vanyu]

Thanks guys! That's defintely another idea to ponder. I might have not explained myself very well when I said "crank it up" I still rely mostly on preamp distortion, right now I'm only playing on 2 on the volume knob but, at the very, very most, I'd be going up to 5 or so. Would I be still at risk of throwing more than 100w into the cab?

I would still highly recommend pulling tubes with the MV at 5. I know with my 2203, 5 is still EXTREMELY loud, and right at the point of power tube break up, which I would guesstimate to be around 100-120w of output. And besides, it's a lot quicker pulling two tubes than rewiring the entire cabinet. 1 minute vs 1 hour. Just make sure you pull either V5 and V8 OR V6 and V7

These 100w heads were designed to be ran as full stacks, and should be ran as such if you wish to keep your nice Celestions original.

 

[BWOTW]

I would still highly recommend pulling tubes with the MV at 5. I know with my 2203, 5 is still EXTREMELY loud, and right at the point of power tube break up, which I would guesstimate to be around 100-120w of output. And besides, it's a lot quicker pulling two tubes than rewiring the entire cabinet. 1 minute vs 1 hour. Just make sure you pull either V5 and V8 OR V6 and V7

These 100w heads were designed to be ran as full stacks, and should be ran as such if you wish to keep your nice Celestions original.

Thanks man, much appreciated. Indeed, the simpler and quicker the better. But, as far as I understand by reading some posts over here (this is all new to me), pulling two tubes to make it a 50watter requires a rebias, right? And that would mean a visit to the tech for me...