Speaker questions

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Speaker questions

Postby jeffm725 » Fri Sep 05, 2008 6:50 am

gotta a couple questions regarding speaker loads.

1) in a 2x12 cabinet wired parallel (using 2 8 ohm speakers so it is a 4 ohm cabinet) can you use 2 different speakers of wattage rating? For example Could I run a 300 Watt JBL e-120 and a 50 watt Tone tubby together? I understand that maybe it will sound like shit together, but my concern is will it hurt the speaker or the amp?

2) On a twin reverb there is a jack for an extension cabinet. That jack recomends a 4 ohm load. Can you plug a single 8 ohm speaker cab safely into that extension jack? or is it absolutely required that it be a 4 ohm load. Will running a single 8 ohm extension cab hurt the amp? Or the speaker?


I just picked up a 1968 Twin Reverb, the thing is that one of my JBL e120's is being reconed so i only have 1 available for this weekends gigs. I would like to able to use the JBL in some manner with the Twin for obvious reasons.
In addition to the e-120, I also have 2 Tone Tubbies and 2 old Celestion G12 75 (75 watt..and these are the old ones, not the newer G12"T" 75) to choose from

Thanks,
Jeff
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Postby strumminsix » Fri Sep 05, 2008 7:37 am

IIRC the amp only worries about ohms.

Fenders, on average are safe one mismatch up or down.

I think you'd be fine with just one e120.

I ran my '68 Dual Showman Reverb for I don't know how long before realizing one of my speakers was blown! Also Fenders of that age are not multi-tap off the OT so the ext speaker jack will always lower your impedance without any circuit changes.
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Postby RiverRat » Fri Sep 05, 2008 8:10 am

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Last edited by RiverRat on Tue Feb 22, 2011 10:12 am, edited 1 time in total.
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Postby jeffm725 » Fri Sep 05, 2008 8:30 am

Thanks for the info!

So maybe in this particular case as I understand it that I just leave the 2 celestions in the Twin as the "main speakers" and then I would be pretty safe plugging a single JBL 8 ohm cab in the extension slot?
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Postby tigerstrat » Fri Sep 05, 2008 10:34 am

jeffm725 wrote:Thanks for the info!

So maybe in this particular case as I understand it that I just leave the 2 celestions in the Twin as the "main speakers" and then I would be pretty safe plugging a single JBL 8 ohm cab in the extension slot?


I hate to mix speakers. Try running just the single JBL for an 8ohm load. Compare that to the Celestion pair, and then try them all together. I would bet that the JBL by itself sounds best.
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Postby playingdead » Fri Sep 05, 2008 11:06 am

I have a few spare E120's Jeff ... if you're in need.

Regarding the wattage difference, the only danger is blowing the Tone Tubby, depending on how efficient it is compared the JBL. You might have trouble "hearing" the E-120 or vice versa as you turn the amp up.

Too-low is better than too-high for tube amps, I think, so I wouldn't be too worried about blowing an output transformer or anything.

But what do I know ... LOL
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Postby quacktron » Fri Sep 05, 2008 11:07 am

Just to keep the details straight, The extension doesn't recommend a 4ohm load. The total load on the amp should be 4ohms. The external speaker jack is wired in parallel with the internal 4ohm (8&8)speakers. So you can't really run it at 4ohms with an extension cab unless you disconnect at least one of the internal speakers.

Anywaze, if you plug your 8ohm e120 speaker into the extension jack, and leave the internal speakers you'll have a 2.67ohm load, which would be a mismatch.

I also have a 68 Twin Reverb and my amp tech (30yrs working on twins) says it'll be fine @ 2.67 ohms. In fact my twin, which I acquired from the original owner (for $100) was run @ 2ohms for over a decade. 4x12.

so many options, you could
run it with the extension speaker @ 2.67
disconnect the internals, connect the extension and run it @ 8
disconnect one of the internals, connect the extension and run it at 4

you can also pull 1 set of power tubes and the amp will want to see 8

you could remove one of the internals and install your e120, and then replace the other when you get the recone back, and then you get the award for the heaviest amp ever. BUT SOUNDS SOOO GOOD!
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Postby quacktron » Fri Sep 05, 2008 11:12 am

I hate to mix speakers. Try running just the single JBL for an 8ohm load. Compare that to the Celestion pair, and then try them all together. I would bet that the JBL by itself sounds best.


+1 for the single E120 @ 8ohms
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Postby strumminsix » Fri Sep 05, 2008 11:33 am

quacktron wrote:
I hate to mix speakers. Try running just the single JBL for an 8ohm load. Compare that to the Celestion pair, and then try them all together. I would bet that the JBL by itself sounds best.


+1 for the single E120 @ 8ohms


+2 that is what i was eluding to in my first post.

my speakers are weber neomags that are d120 clones.
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Postby jeffm725 » Fri Sep 05, 2008 12:14 pm

playingdead wrote:I have a few spare E120's Jeff ... if you're in need.

Regarding the wattage difference, the only danger is blowing the Tone Tubby, depending on how efficient it is compared the JBL. You might have trouble "hearing" the E-120 or vice versa as you turn the amp up.

Too-low is better than too-high for tube amps, I think, so I wouldn't be too worried about blowing an output transformer or anything.

But what do I know ... LOL



thanks vic, I may just take you up on that (e-120) I had gotten a pair recently and when I received them they looked different than any e-120's I ever had cone wise. It turns out the previous owner went nuts doping them. I mean, seriously, it looks like someone just took a gallon of shellack (sp?) or varnish and poured it over the cones. They shine !!:? Another Ebay beware deal, that didnt show up in the pics.
I didnt know how much of a diffence it would make sound wise and I didnt have a ton of scratch laying around so I decide to recone one at a time to compare the doped one vs. the recone. Well I got the 1st recone back and sure enough the doped speaker sounded like ass compared to the recone (ATC - springfield- did recone) so I sent the second in for the recone and that is where it is now. I had one spare but my daughter thought the aluminum dust cover was nice and shiny and pressed it in and indented it, I tried sucking it back out with a vacuum and it tore! (the dust cap not the cone, thank god)

picked up a sweet 68 Twin, its got the mojo :-)
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Postby jeffm725 » Fri Sep 05, 2008 12:19 pm

tigerstrat wrote:
I hate to mix speakers. Try running just the single JBL for an 8ohm load. Compare that to the Celestion pair, and then try them all together. I would bet that the JBL by itself sounds best.


Thanks Tom,
The speaker mixing wasn't my favorite option by a long shot. I have just always run 2 jbls together(or 2 tone tubbies, or 2 celstions or 2 whatevers) and I have a sweet new (old) twin, that I dont wanna mess up so I was hesitant to show it anything but a 4 ohm load. If it is safe to run a single 8 ohm JBL out of the Twin, then that is what I am gonna do :smile:

Best bet would just unplug the 2 celestions that run out of the main speaker jack and plug my single jbl into that jack, right?
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Postby quacktron » Fri Sep 05, 2008 12:43 pm

It's safe, but the sound is a little less clean.
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Postby jeffm725 » Fri Sep 05, 2008 1:02 pm

quacktron wrote:It's safe, but the sound is a little less clean.

thanks very much for the help!
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Postby playingdead » Fri Sep 05, 2008 9:24 pm

What did the recone run, Jeff? Factory parts or aftermarket?

I have two mint E-120s in my stage cabinet, one spare mint fresh-factory recone E-120, one near-mint E-120 with a couple of minor dustcap wrinkles, and one E-120 that is not cosmetically nice (small repair) but sounds fine.
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Postby jonarobb » Sat Sep 06, 2008 1:44 am

Flyback voltage is enough of a deterrent not to run any kind of upward impedance mismatch on a beautiful 68' Scumacher tranny. Will it happen immediately? It could. Do you want to chance it for being able to use a JBL for a gig? Those transformers are spec'd new for being able to perform with a mismatch either way only to address the amount of speakers being blown back then. It wasn't a long term performance idea, or to give the user some kind of flexibility in impedance selection. Your transformer is 40 years old. You're asking for trouble. The OT doesn't smell so good when it cooks. And the carbon is a bitch to scrap off the chassis if the flyback arcs out anywhere. I recommend being patient and not chancing the mismatch.
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