Ohm / wiring question - 3x10" combo, 15ohm speakers

[mjet]

I have an old CMI (Marshall spinoff from the 70s) transistor combo amp that has 3 10" speakers. Here's a photo:







They're 15ohm, 10" Celestions (and yes, one had a rake handle-sized hole through the cone - I had no trouble believing the seller when he told me that it spent 10 years in a backyard shed). I've taken them out so that I can give the cabinet a thorough cleaning. What would the impedance from the amp be? There isn't a jack for the speaker wire - it comes straight out of the chassis so I'll have to rewire it up eventually.

I'm torn whether to keep such lovely speakers in what will likely be at best a decent little amp for clean tones. That's got me thinking that I should keep the two good Celestions aside and just buy some cheaper replacements. I could also just get a pair of 10" speakers but that wouldn't allow me to recreate the ohmage of the original setup. Any thoughts?

[JazzBlaster]

a good explaination of speaker wiring

[OffYourFace]

15 ohms is an old term for what we now know as 16 ohms.  If you've got (3) 16 ohm speakers then the amp would have a 4 ohm transformer.

[mjet]

a good explaination of speaker wiring

Good resource - here's what I found concerning three speaker setups.



So I think it's safe to presume that the factory-spec load coming out of the amp was between 4-5 ohms.

[blacktiger]

So I think it's safe to presume that the factory-spec load coming out of the amp was between 4-5 ohms.

While that seems the most logical answer, those speakers sure as hell look like they're wired in series to me...

[Orang Goreng]

While that seems the most logical answer, those speakers sure as hell look like they're wired in series to me...

Yep, otherwise the number of wires coming from them doesn't make sense, IMHO.

[luau]

Those speakers are wired parallel. If you need convincing, draw the speakers and wiring on paper and then see which of the two diagrams in mjet's post you can convert your drawing to.

edit: I just thought of a handy way to identify the two. If we let red be hot and black be ground then: red-to-red: parallel, red-to-black: series. Kinda like coral snakes but without the nasty bite.

[blacktiger]

Those speakers are wired parallel. If you need convincing, draw the speakers and wiring on paper and then see which of the two diagrams in mjet's post you can convert your drawing to.

edit: I just thought of a handy way to identify the two. If we let red be hot and black be ground then: red-to-red: parallel, red-to-black: series. Kinda like coral snakes but without the nasty bite.

You're right.  Three speakers somehow make it a lot more confusing than two, damn them!

[OffYourFace]

def. parallel.  yeah, there's no way they'd put a 48-ohm tranny in there 

I did a lot of studying regarding 3 and 6 speaker cabs.  6 spkr cabs are the strangest because  you have to get custom speakers for them.  Either 6 ohm or 24 ohm.
I had a custom 6x10 bass cab w/ 24 ohm spkrs.  It was  a 4 ohm cab.