Connecting 15" Speakers to Fender Twin Reverb

Jim Cooley · From: The 'Ville, Texas, USA

I am thinking about getting one or two 15" speaker cabinets to use with my 1973 Fender Twin. My idea is to keep the Twin the 12" speakers to use for six string guitar, and when I want to use it for steel, unplug the 12" speakers and plug in the 15s. Since it's a 4 ohm amp, am I correct in thinking that it's an even swap if I use one 4 ohm 15 inch speaker? How do I connect the 15s and still maintain 4 ohms if I use two speakers?

Is there a better way to do this other than mounting the head and speakers in three or four separate cabs?
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Hey, mister, how do you pedal that thing anyway?

"The worst an honest man can do is make an honest mistake" - Augustus McCrae
"From the sweet grass to the packing house, birth 'til death, we travel between the eternities" - Prentiss Ritter

Too many steels, amps & other stuff, and an open mind. I have tube amp bias.

Ken Fox · From: Nashville GA USA

Two 8 ohm speakers in parallel or two 4 ohm in series

Roger Kelly · From: Bristol,Tennessee

Jim, since you have two 8 ohm 12 inch speakers in your Fender twin wired in parallel...I would use two 15 inch 8 ohm speakers. That way you can use both Speakers hooked in parallel + to + and - to - and your Twin will have the same 4 ohm load as with the 12 inch speakers.
You could use one 15 inch 8 ohm speaker without damage but your power will not be the same 85 watts. It would be around 40-50 watts would be my guess.
Do not switch speakers with the power switch on.
This is what I would do.

Jim Cooley · From: The 'Ville, Texas, USA

Thanks, Ken.

I don't know why it's hard for me to keep this straight. Maybe because I haven't dealt with it in a very long time. I have to dumb this way down.

If I use one 4 ohm speaker, I can just unplug the 12" speakers and plug in the 15, right?

To keep the amp at 4 ohms with 2 x 4 ohm speakers, would I go from the Speaker jack on the Twin to one 15" cabinet, then from that speaker to the second 15? If I go from the amp's Speaker jack to one 15 and from the Ext. Speaker to the other 15, wouldn't that be a 8 ohm load? Or is it the opposite...or entirely different?

I suddenly feel like a bad blonde joke, and I don't even have hair.

Ken Fox · From: Nashville GA USA

If I use one 4 ohm speaker, I can just unplug the 12" speakers and plug in the 15, right?

Yes that is correct

To keep the amp at 4 ohms with 2 x 4

ohm speakers, would I go from the Speaker jack on the Twin to one 15" cabinet, then from that speaker to the second 15? If I go from the amp's Speaker jack to one 15 and from the Ext. Speaker to the other 15, wouldn't that be a 8 ohm load

No, that can't be done with 2- 4 ohm speakers. The result would be a 2 ohm load. You would need two 8 ohm speakers to do that.

Jim Cooley · From: The 'Ville, Texas, USA

Ah, now the light comes on. It's a dim bulb, but it's on. I think. So, it's one 4 ohm speaker or 2 x 8 ohms? Thanks.

Dave Grafe · From: Hudson River Valley NY

Riley Hart · From: South Carolina, USA

One stupid question;
Given the fact that the older fenders that were designed with only the one tap on the OT were specifically meant to be operated into a load of no less than 4 ohms, and given that the two 12's produce this 4 ohm load;

Why did they install the extra jack to run an external 8 ohm load? I calculate the load with the stock speakers and an external 8 ohm load to be 2.67 ohms total load impedance.

What am I missing here?

Like I said, stupid question lol...

Riley Hart · From: South Carolina, USA

Excuse me; that is 3.2 ohms - i found the slide rule app on the phone before i could find the calculator, and misread the cursor - still, 3.2 ohms?

Riley Hart · From: South Carolina, USA

No i was right the first time - guess i better start a thread about slide rules!

Riley Hart · From: South Carolina, USA

No i was right the first time - guess i better start a thread about slide rules!

Jim Cooley · From: The 'Ville, Texas, USA

I have seen some cabinets with two 1/4" jacks. Is one jack "in" and the other one "out" so they can be used in 2 speaker applications? If not, how are the speakers connected? If I use two 8 ohm cabs, do I run from the amp's speaker jack to the 1/4" jack in one cab, then to the 1/4" jack in the second cab? Or do I need to go from the speaker jack to the (+) and (-) terminals on the first speaker, then from the (+) on the first speaker to the (+) on the second speaker and then connect the two speakers' (-) terminals? I don't mean to be dense, but I can't help feeling that way...and stupid...and...

Riley - I have read several forum postings that try to address your question and I don't understand why Fender did that either. You used a slide rule? Cool. I didn't think anybody used them any more.

Riley Hart · From: South Carolina, USA

Jim - If I understand correctly, whenever you daisy-chain the two cabinets with a cable from the output jack on the first, in most cases(if there aren't any special crossover networks being used), you would in-effect be doing the same thing as running the cable directly from one speaker + and - to the other, as normally the two jacks are just there for convenience, and wired in parallel. You 'can' run into trouble if whoever wired the speakers didn't take into account the correct 'phasing' which I understand is different on Black widows and Jbl's. Perhaps not in every case, but I would check.

You'd still be running in parallel and the same rules would apply impedance-wise, but the sound wouldn't work good because the speakers would see + to - instead of + to +, in effect causing them to work against one another.

As an aside, and I won't hijack the thread, I have used slide rules a lot in daily calculations. Consider them quicker and more effective than digital calculators in certain cases such as ratios and proportions. I got good with them once or twice, but at my age if you don't do something every day, you forget real quick lol...

.

rodger_mcbride · From: Minnesota

Bill A. Moore · From: Silver City, New Mexico, USA

It is my opinion that Leo wasn't too worried when he added the extra output jack. Lower resistance is better for a tube amp output than high resistance, The main speaker jack shorts to ground, (low resistance) when the plug is pulled to save the amp from high resistance output. I don't know the minimun necessary for a 4 ohm output, but over the years I've seen Twins plugged into Bassman, Dual Showman, and even a Marshall 4x12 cab with no ill effects.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Provided you don't play with distortion or at "maximum sustained volume", the old tube Twin Reverbs will do just fine pushing only 2 ohms. I've run them all day and night this way, and never had a problem. In other words, these Fender amps were actually designed to be run like this. Where you have to be careful is if you're running extra speakers on an amp that has no external speaker jack.

The absence of an external speaker jack usually means that running extra speakers is not recommended. When you have an external speaker jack, it's evidence they have factored in the extra load for running additional speakers, provided their impedance isn't less than the speaker(s) in the amp.

Riley Hart · From: South Carolina, USA

...that's about the best explanation I've heard. stated very eloquently and to the point.

...tnx for addressing it...

Clete Ritta · From: San Antonio, Texas

Jim Cooley · From: The 'Ville, Texas, USA

Hey thanks everybody.

Donny - that is the best explanation I've read. It makes sense.

Clete - Your suggestion falls right in line with my line of thought. I have one more 4 Ohm, 15" speaker than I have cabinets. I have been thinking about putting in a cabinet, unplugging the 12" speakers and plugging in the 15" for steel. If I eventually decide I want to go with 2 x 15" speakers, I'd need two 8 ohm speakers and another cabinet to keep the load at 4 ohms. I can see what's coming, though. I'm going to end up putting the Twin head in a separate cabinet for versatility and weight reduction, right?

Thanks again, y'all - great information.

Clete Ritta · From: San Antonio, Texas

Others here have done that with their combos with impressive results:

James Morehead:

Ricky Davis:

Im like you, I have a Twin and a single 4 ohm 15" JBL in an extension cab. You can use the ext cab only as a main speaker at 4 ohms, or plug it in as an extension cab with the internal 2X12". It wont kill the amp, but it wont perform optimally at a less than 4 ohm load. BTW I think guitar sounds pretty darn good thru 2X15" too. Wink

Clete

Jim Cooley · From: The 'Ville, Texas, USA

Clete - I have seen these before. Now you have me drooling again.

Tommy Bannister · From: Hampshire, UK

HI GUYS CAN ANYBODY DRAW THEDIFFERENCE BETWEEN PARALAL AND SERIESWIRERING I'M COPLEATLY COFUSED
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GOT EVERYTHING a steelplayer needs except movement owing to a bad stroke
paralizing my compleat left side

may god grant me return of it all!!
williams d10 9/8 burnt orange box,bobro,itone,rowland space echo,goodridge ldr 120 VP,any bars,quad reverb,sonar 8.5 vegus 10,soundforge, plus foxtex 24/24,maki 16 trk desk,could go on forever,two Nashville 112's pevey 500 session, steel guitar black box,LDR 120 VP

brand new WILLIAMS D10 9,8 NOT PLAYED OWING TO MY STROKE,WHAT A BUMMER!!!

Clete Ritta · From: San Antonio, Texas

Series:

A loop like batteries in a flashlight pos to neg thru each speaker.

Parallel:

All pos combined and all neg combined.

look here to see explanations of series and parallel speaker wiring.

Clete

Tommy Bannister · From: Hampshire, UK

yhanks alot fot your post Clete Ritta you forum members are out of this world.I understand your drawings,and is much appreciated
Clete Ritta good dy and luck to you and yours.
_________________
GOT EVERYTHING a steelplayer needs except movement owing to a bad stroke
paralizing my compleat left side

may god grant me return of it all!!
williams d10 9/8 burnt orange box,bobro,itone,rowland space echo,goodridge ldr 120 VP,any bars,quad reverb,sonar 8.5 vegus 10,soundforge, plus foxtex 24/24,maki 16 trk desk,could go on forever,two Nashville 112's pevey 500 session, steel guitar black box,LDR 120 VP

brand new WILLIAMS D10 9,8 NOT PLAYED OWING TO MY STROKE,WHAT A BUMMER!!!

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