Old Marshall head speaker question

[Cowbell Bill]

I have a 1977 Marshall head 50 watt. 2 speaker outs. I'm using 1 out into a 4 10 cabinet crappy speakers. I would like to use the 2 outputs into 2 12 " speakers 8 ohms each (better speakers) There's a jumper on the back of the amp 4-8-or 16 ohms. So 1 output to a single 8 ohm speaker and the other output to the other 8 ohm speaker. right now the jumper is set for 8 ohms. Any help? Thanks Bill

 

[miroslav]

If you do it that way...1-to-8 Ohm and 2-to-8 Ohm....ideally, you need to set the head to 4 Ohms.

That's just a parallel speaker output...

Are those two 12" speakers in a cab together?
You then only need to run one cable from one speaker output of the amp...and then just connect the speakers inside the cab in either parallel (4 Ohm) or series (16 Ohm).

Here...maybe this will help you: http://www.bcae1.com/spkrmlti.htm

 

[Cowbell Bill]

If you do it that way...1-to-8 Ohm and 2-to-8 Ohm....ideally, you need to set the head to 4 Ohms.

That's just a parallel speaker output...

Thanks Miroslav, Thats where I get lost. 1 out to 1- 8 ohm speaker. 2nd out to 1- 8 ohm speaker, set the jumper to 4 ohms. Gotcha

 

[Lt. Bob]

Thanks Miroslav, Thats where I get lost. 1 out to 1- 8 ohm speaker. 2nd out to 1- 8 ohm speaker, set the jumper to 4 ohms. Gotcha

the way it works is (assuming all speakers are the same impedance) if the speakers are hooked up parallel, then take the ohms and divide by the number of speakers. ( 8ohms divided by two speakers is 4 ohms.)
If you hook the speakers up in series, then it's the impedance times the number of speakers so two 8 ohm speakers would be 16 ohms.
Since the two jacks in the back are parallel, in this case 2-8ohm speakers would be 4 ohms. It would be the exact same thing if you ran only 1 cable out of the amp and simply had the two speakers daisy chained or in a single cab in parallel.

 

[darrin_h2000]

Ive had 2-12 cabinets set up to work in stereo with each being 16ohm speakers and seperate leads to each speaker. So if one speaker works when it is hooked up with one lead this might be the case...then you would use the 8ohm setting...well depending on what is inside the cabinet.