Need some help wiring a cab

Reinhard

I got these greenbacks for a good price, so I thought I'd give them a twirl in my 2x12. They are 16 ohms, 25W, looks like voice coils have been replaced, but good shape otherwise.
I want to wire these parallel so the cab is 16ohm. Do I wire the two cables from the input jack so each go to the positive tab on the speaker, and then solder a cable between the negative tabs of each speaker? What is positive and what is negative on these, or do I just match the colours?
What input jack and wire do I need? The original speakers in the cab have little tabs you just slide the connectors onto, these will need solder.

Any tips would be great.
Thanks to MikeM for giving me a headsup on these.
Reinhard

ezietsman

Two 16 Ohm speakers cannot be wired to give 16 Ohm. Parallel gives 8 and series gives 32.

Reinhard

ez wrote: Two 16 Ohm speakers cannot be wired to give 16 Ohm. Parallel gives 8 and series gives 32.

Brainfart. 8 will do just fine, can't use 32ohm.

So how do I wire it?

ezietsman

Reinhard wrote:
ez wrote: Two 16 Ohm speakers cannot be wired to give 16 Ohm. Parallel gives 8 and series gives 32.
Brainfart. 8 will do just fine, can't use 32ohm.

So how do I wire it?

jack tip to positive on spk1. jack ground to negative on spk1. then connect positive of speaker 2 to positive on speaker 1 and ditto for negative.

make sure by measuring the resistance. should be around 6 ohm.

Reinhard

Sweet! Thanked

Reinhard

How do I know which is positive and which is negative?

ezietsman

It doesn't matter. ac going through them. just keep it consistant between the speakers else you'll have phasing issues.

shaunf

Reinhard wrote: I got these greenbacks for a good price, so I thought I'd give them a twirl in my 2x12. They are 16 ohms, 25W, looks like voice coils have been replaced, but good shape otherwise.
I want to wire these parallel so the cab is 16ohm. Do I wire the two cables from the input jack so each go to the positive tab on the speaker, and then solder a cable between the negative tabs of each speaker? What is positive and what is negative on these, or do I just match the colours?
What input jack and wire do I need? The original speakers in the cab have little tabs you just slide the connectors onto, these will need solder.

Any tips would be great.
Thanks to MikeM for giving me a headsup on these.
Reinhard

Bastard! I wanted them. Contacted the buyer on Sunday morning and was discussing making a deal with him on email when he all of a sudden went quiet, and then only responded again last night telling me they were sold! ☹

What makes you think the voice coils have been replaced?

AlanRatcliffe

Mmm... nice Reinhard.

shaunf wrote: What makes you think the voice coils have been replaced?

Speaking for myself, I usually take glue around the dust caps to mean the coils have been replaced. It can also mean that the dust caps were loose or replaced, but usually it points to a recoil.

shaunf

Reinhard, here is a diagram that might help make things clearer:

@ Alan: Thanks for the info. Is/was this sort of voice coil replacement fairly common here? I mean, who can do this sort of work?

Also, don't quote me on this, but I'm pretty sure that when I removed the 4 greenbacks from my cab when I restored it, I seem to recall all 4 speakers having a very similar darker area around each of the dust caps, and that it look consistent between the speakers. I just wonder about the liklihood of all these speakers having had the dust caps removed at some point.

shaunf

Some more info on those speakers if you're interested:

They are G12H speakers, conservatively rated to 25w, but were later rated 30w with no changes to the speaker.
Both date to January 1972
They probably have the 55hz bass cones. Look on the back of the cones, probably on the same side as the solder tags, there should be a code stamped on the cone. Tell us what this code is of you want to verify if they are the lead or bass cones, and whether the cones are original.
They should be Marshall specific Greenbacks. Did they come out of a Marshall cab?

Reinhard

Alan Ratcliffe wrote: Mmm... nice Reinhard.

shaunf wrote: What makes you think the voice coils have been replaced?
Speaking for myself, I usually take glue around the dust caps to mean the coils have been replaced. It can also mean that the dust caps were loose or replaced, but usually it points to a recoil.

Thanks Alan! I think they have been replaced, because I had A Weber repaired and it looked the same post surgery, but I could be mistaken.

shaunf wrote: Reinhard, here is a diagram that might help make things clearer:

@ Alan: Thanks for the info. Is/was this sort of voice coil replacement fairly common here? I mean, who can do this sort of work?

Also, don't quote me on this, but I'm pretty sure that when I removed the 4 greenbacks from my cab when I restored it, I seem to recall all 4 speakers having a very similar darker area around each of the dust caps, and that it look consistent between the speakers. I just wonder about the liklihood of all these speakers having had the dust caps removed at some point.

Then I just beat you! I mailed him Saturday evening around 11pm. Thanks for all the info ShaunF (thanked). I think the seller said they came out of a marshall 2x12 cab.

The codes are 102/3 on both speakers?

shaunf

Reinhard wrote:
The codes are 102/3 on both speakers?

102/3 will make them 75hz "Lead cones" made by Pulsonic.

I must pull one of my speakers again and check the dust cap. Maybe the strip of darkness around them was narrower. I do recall that they did not look like any work had been done on them.

*Edit* Forgot to mention, you beat me fair and square then! ? Glad they went to a good home! 8)

AlanRatcliffe

shaunf wrote: @ Alan: Thanks for the info. Is/was this sort of voice coil replacement fairly common here? I mean, who can do this sort of work?

Bothner's used to have a whole speaker repair department led by a chap called Keith (an MD of all things) and the very talented Mandy, but once the two of them left, they started picking up problems. These days they seem to refer recones to others, but I'm not sure who it is.

Also, don't quote me on this, but I'm pretty sure that when I removed the 4 greenbacks from my cab when I restored it, I seem to recall all 4 speakers having a very similar darker area around each of the dust caps, and that it look consistent between the speakers. I just wonder about the liklihood of all these speakers having had the dust caps removed at some point.

It's all got to do with how the speaker ages and fades. With a full recone you don't usually see the repair, but the cone will look newer than the rest of the speaker. With a recoil, the dustcap and surrounds will be newer/darker than the cone. With just the dustcaps replaced, they will be new, and if it's the old dustcaps reglued, you see the darker glue line only (and it's usually thicker than the factory job). There is however, lots of grey area between that can make being certain difficult.