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Post subject: Super 210 Ext Cab
Posted: Sat Aug 29, 2015 12:36 pm
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If I connected an Ext. Cab rated at 50 watts to this amp would it blow out the speakers? Even if I'm not playing at top volume? I already have a 2x12 cab and can get a great deal on two 25 watt Celestion G12M Rolas. Thanks.


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Post subject: Re: Super 210 Ext Cab
Posted: Sat Aug 29, 2015 1:48 pm
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A safer and more sensible bet would be Celestion's V30, rated at 60 watts apiece.

Arjay

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Post subject: Re: Super 210 Ext Cab
Posted: Sat Aug 29, 2015 2:35 pm
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Retroverbial wrote:
A safer and more sensible bet would be Celestion's V30, rated at 60 watts apiece.

Arjay


I definitely agree that getting two speakers that equal 60watts or more is ideal. I also agree on the Vintage 30's being my first choice. I can get a great deal on a pair of 30's, but they're both 8ohm; the Super 210 Ext Cab calls for an 8ohm Ext. Maybe I could get one of the cheap G12M's and then find a 16ohm Vintage 30. I wonder how the two would sound together.

But back to my initial question...I'd just be asking for trouble using a 50watt cab, eh? Even if I don't crank the amp at 100%? I figured as much.


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Post subject: Re: Super 210 Ext Cab
Posted: Sat Aug 29, 2015 3:16 pm
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At a minimum, I recommend a 50% reserve power-handling capacity between a speaker system and the amplifier (100% would be even more prudent). Using these guidelines, I haven't blown a speaker in over four decades and I've been known to dime my Twin Reverbs and Dual Showmans on occasion.

Your 60-watt Super Amp will likely behave just fine with a pair of G12M's but frankly, I think the V30 is a nicer sounding speaker and it offers a better margin of safety in the event of some calamity.

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Post subject: Re: Super 210 Ext Cab
Posted: Sat Aug 29, 2015 3:27 pm
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Retroverbial wrote:
At a minimum, I recommend a 50% reserve power-handling capacity between a speaker system and the amplifier (100% would be even more prudent). Using these guidelines, I haven't blown a speaker in over four decades and I've been known to dime my Twin Reverbs and Dual Showmans on occasion.

Your 60-watt Super Amp will likely behave just fine with a pair of G12M's but frankly, I think the V30 is a nicer sounding speaker and it offers a better margin of safety in the event of some calamity.

Arjay


I agree w/ everything you're saying, my only problem is I'm cash poor. It's too bad that I couldn't run the two 8ohm 30's at a combined 8ohms.

I tend to agree that the amp is "likely behave just fine" w/ the two G12M's, but the "likely" comment is def cause for some concern. If something did go wrong it would just be on the speaker end, right?

Anyone here have any experience combing a g12m w/ a vintage 30? Seems like an interesting combo.


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Post subject: Re: Super 210 Ext Cab
Posted: Sat Aug 29, 2015 3:37 pm
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Adam O'Blivion wrote:
If something did go wrong it would just be on the speaker end, right?


Correct.

If you're playing your 60-watt amp at extremely high volume and you happen to lose one of your 50-watt speakers, the remaining driver will immediately be carrying that 60-watt output. In that scenario you could conceivably lose both speakers before you realized there was a problem. That's my concern and I have seen it happen before.

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Post subject: Re: Super 210 Ext Cab
Posted: Sat Aug 29, 2015 5:13 pm
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Retroverbial wrote:
If you're playing your 60-watt amp at extremely high volume and you happen to lose one of your 50-watt speakers, the remaining driver will immediately be carrying that 60-watt output. In that scenario you could conceivably lose both speakers before you realized there was a problem. That's my concern and I have seen it happen before.


Just to clarify, the G12M's are 25watts each. I'm guessing that was just a typo on your end, "lose one of your 50-watt speakers"?

Also, there is no way to wire two 8ohm speakers for 8ohm output, just 4 or 16, right?

One more thing... I noticed in the ad for the G12M's, one mentions an "open voice coil" The other mentions "Damaged tinsel lead out, radial edge tear." What does open voice coil mean? In terms of the second speaker's issues, what type of repairs are needed? Or would you need more info? Thanks for all the help.


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Post subject: Re: Super 210 Ext Cab
Posted: Sat Aug 29, 2015 5:27 pm
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An "open" voice coil means that the speaker is blown.

As for the second speaker, a "radial edge tear" would seem to indicate that the cone's surround has been compromised by mishandling or abuse.

In both instances the only recourse is to have both speakers re-coned.

I wouldn't walk away from a deal such as that......I would run!

Two 8Ω speakers can only yield one of two total impedances: 4Ω (wired in parallel) or 16Ω (wired in series).

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Post subject: Re: Super 210 Ext Cab
Posted: Sat Aug 29, 2015 5:35 pm
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Retroverbial wrote:
An "open" voice coil means that the speaker is blown.

As for the second speaker, a "radial edge tear" would seem to indicate that the cone's surround has been compromised by mishandling or abuse.

In both instances the only recourse is to have both speakers re-coned.

I wouldn't walk away from a deal such as that......I would run!

Two 8Ω speakers can only yield one of two total impedances: 4Ω (wired in parallel) or 16Ω (wired in series).


Yeah, so it looks like it's back to the drawing board. I'm still aggravated at the pair of 8ohm Vintage 30's in a 2x12 combo, minus the amp, for only $120. It's a great deal. If only they were 16ohms. I'm thinking about buying them anyways, but then I'd have to wait on finding someone interested in a trade for them, or even better, someone who has two 16ohm 30s and need two 8's.


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Post subject: Re: Super 210 Ext Cab
Posted: Mon Aug 31, 2015 9:35 am
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On another forum I was talking about my amp's ext speaker being labeled at 8ohms. This was one of the responses:

"ya can re-wire your 8 ohm speakers is series...If you wire the speakers in series it adds up to 16 ohms. Then you can run the cab at maximum by running the amp at 16ohms. It's louder...as long as your amp is seeing 8Ω or greater then it'll be a-ok. When it sees less than 8Ω is when too much current gets pulled and your transformer overheats, melts the windings, and shits the bed."

Is this guy correct or does he have no idea what he's talking about?


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Post subject: Re: Super 210 Ext Cab
Posted: Mon Aug 31, 2015 4:31 pm
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That's the prevailing internet dogma. However, the fact is that it is perfectly fine to use an amp rated for 8 ohms with a 4 ohm speaker load, it only means that the amp will not develop full power. In fact, I routinely run several of my amps at half of the rated impedance, and have done so for years with zero problems.

The best advice is to keep any impedance mismatch on a tube amp to within a 2 to 1 ratio, high or low and you will be fine. It's all about fear of the unknown, and those that spout off about impedance mismatches on a tube amp simply don't know about what they say, they are just afraid without justification. Many times, a slight mismatch can produce a sweeter sound than when matched, which is why I do it.

Impedance changes with frequency, and if a mismatch caused harm to a tube amp they would all blow every time they were used due to the constantly changing frequency of the output.

Get those V30s and enjoy them. I am using a 2x12 cab with V30s (4 ohm) on a few 8 ohm rated amps and they sound fantastic. My favorite is a MB TA15, using the 8 ohm out from the amp, sweet! Yes, I crank it often. :wink:

As Retroverbial correctly pointed out, your real worry is to be sure that your speaker wattage can handle the output of the amp, and the 100% margin of error, i.e. twice the speaker wattage as the amp, is wise advice.

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Post subject: Re: Super 210 Ext Cab
Posted: Mon Aug 31, 2015 4:50 pm
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shimmilou wrote:
That's the prevailing internet dogma. However, the fact is that it is perfectly fine to use an amp rated for 8 ohms with a 4 ohm speaker load, it only means that the amp will not develop full power. In fact, I routinely run several of my amps at half of the rated impedance, and have done so for years with zero problems.

The best advice is to keep any impedance mismatch on a tube amp to within a 2 to 1 ratio, high or low and you will be fine. It's all about fear of the unknown, and those that spout off about impedance mismatches on a tube amp simply don't know about what they say, they are just afraid without justification. Many times, a slight mismatch can produce a sweeter sound than when matched, which is why I do it.

Impedance changes with frequency, and if a mismatch caused harm to a tube amp they would all blow every time they were used due to the constantly changing frequency of the output.

Get those V30s and enjoy them. I am using a 2x12 cab with V30s (4 ohm) on a few 8 ohm rated amps and they sound fantastic. My favorite is a MB TA15, using the 8 ohm out from the amp, sweet! Yes, I crank it often. :wink:

As Retroverbial correctly pointed out, your real worry is to be sure that your speaker wattage can handle the output of the amp, and the 100% margin of error, i.e. twice the speaker wattage as the amp, is wise advice.



Interesting. I did some research on this topic, and I read that running a 16ohm cab w/ an amp expecting 8ohms will output half the power (wattage). Also, it will be running the tubes (and amp) extremely hot...lessening the life of the amp. He also said that if the amp expects 8ohms, a cab that's >8ohms will be alright -- a cab that's <8ohms is a very bad decision.


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Post subject: Re: Super 210 Ext Cab
Posted: Mon Aug 31, 2015 5:09 pm
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The facts remain unchanged. A tube output power curve is a parabola, with the peak power output at "matched" impedance. So, if the impedance is higher or lower than matched, the output will be less, meaning less current and less heat. That is the whole idea behind impedance matching, to get the most power from the amp, nothing more.

Just search these forums for even one report of an impedance mismatch within a 2 to 1 ratio causing any harm to a tube amp. The real problem is actually too high an impedance, with an open being the worst case. Using a tube amp with no speaker attached can and does cause damage, hence the shorting output jack on many modern amps. The shorting output jack acts to protect the amp in case it is used with no speaker plugged in. If the factory uses zero ohms (short across the output) to protect the amp, then it only stands to reason that a greater impedance will be fine also. At some point above a 2 to 1 ratio, the impedance is too high and can lead to catastrophic failure of the amp. That point of being too high is really not definable exactly, and that is why we stick to the 2 to 1 ratio.

I put my money where my mouth is, and practice what I preach. If there were any problems with a slight impedance mismatch I would be on here sharing any negative experiences. Again, the facts speak for themselves. Myself, and many other forum members have used tube amps with mismatched speakers with zero problems. Yet there are those who will not accept, or cannot understand the electronic principles behind what I say.

If you are interested in the electronic principles behind tube amp operations, this is an excellent read.

http://www.geofex.com/tubeampfaq/TUBEFAQ.htm#matchspkr

Approximately half way down the page, your specific question is answered in detail.

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Post subject: Re: Super 210 Ext Cab
Posted: Mon Aug 31, 2015 7:12 pm
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Damn! I never should have sold my Marshall 1960a loaded w/ vintage G12-65's. It was 16ohms and I thought I needed an 8ohm. FAHK!!!!!!

Just to recap, The amp's output will remain at 60 watts; it won't get cut in half to 30? Or somewhere in-between...


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Post subject: Re: Super 210 Ext Cab
Posted: Tue Sep 01, 2015 2:08 am
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With an impedance mismatch the amp will not develop full power out, but won't be cut in half, it's not quite that much. That's the reason behind the impedance match, to get the most power from the amp. :wink:

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