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I recently found a Piper (Garnet) 2 x 6V6 amp. In another thread I was told the output transformer is very small. I installed a Celestion 70/80 speaker I had laying around and it sounds way better than the Marsland it replaced. I played the amp at gig levels, up to eight on the dial, for an hour with no problems. Later I realized that the Celestion is 16 ohms and the Marsland is 8 ohms. As I said it worked fine at high volume for an hour. Am I risking damaging the amp if I continue to use the 16 ohm Celestion? I'm not worried about the tubes. They are easily replaced. The output transformer may be hard to come up with an original it it goes. There is a speaker extension jack but the impedance is not labelled on it so I'm assuming it is 8 ohm as well.
 

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Discussion Starter #3
I wouldn't worry about an 8-16 mismatch, unless your output transformer is getting excessively hot, or your losing a lot of output volume.
The 16 ohm Celestion is noticeably louder than the 8 ohm Marsland. I often use a 16 ohm cab with an 8 ohm amp output on newer amps with no problems.I've never worried about it in the past. My worry with this amp is if something does go how hard will it be to get it fixed? A lot of what you read on the Internet says no problem and then others say OK to go lower (e.g. 4 ohm speaker) but not higher. Others say double either way ( 4 or 16) is OK. The output transformer is really small in this amp. I think that's why I like it so much. Great breakup for dirty blues.

I'm going to try it live tonight and see how it goes :)
 

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The concern is normally with respect to using a lower impedance load than the transformer is spec'd for. since the current pulled through the transformer may exceed its ability to dissipate any heat resulting from passing more current. Going the other way - to a higher load than spec'd for -may make the unit misbehave in terms of sound, and there's something that Ibelieve is called reflectance that impacts on tube functioning. But it is not fatal, as I have understood it.

I await the opinion of folks who know more about such matters than I do...which is a pretty long line.

The extra volume from the Celestion is not conspicuous. When one looks at the efficiency specs of speakers, they can vary widely....like, REALLY widely. A more efficient voice-coil with a smaller gap, and a bigger magnet, can easily provide 12db more loudness at 1W than another speaker with a smaller less powerful magnet and inefficient voice-coil.

There's a reason why amp-makers may use a Marsland to produce a budget amp. There's alsoa reason why players replace them with Celestions.
 

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I run my Garnet Rebel at 8 Ohms all the time; the rear panel says "4 Ohms minimum."
 

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There are two camps in regards to the mismatch question. Each of them will swear that their camp is right. I am yet to get a definitive answer on this. In practice, a one step mismatch on either side of the OT rating should be fine. I would think that the smaller the OT, the more risk you are taking on. If it's a hammond in a Traynor, you are sitting pretty good. I have a Traynor YBA-3 Custom Special that I play guitar through. It sounds best with an 8ohm load as that is the only tap on the OT. I have played it on 4 and 16ohms loads and found that I loose power going up a step and gain headroom going down a step. Personally, playing it with a 4ohm load sounds better than a 16ohm load. YMMV. Hardcore tube geeks usually side with the "one step down is safer" mantra about 60% of the time.
 

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On a tube amp the transformer is looking for what it is rated for. If the resistance is lower it alters the voltage to compensate and the voltage is higher than "spec" so it has to dissipate that through heat so transformer gets hot. If it gets too hot it may or may not blow up. The other way around you are just losing efficiency of the amp. I bet an 8 ohm celestion would sound even better than the 16ohm. The amp tries to match the resistance of the 16 ohm by altering voltage lower in this case IIRC, so you are putting a few watts less output of the amp and the amp is straining a bit to do it.
 

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Discussion Starter #9
Played at the blues jam for three hours straight with no problems. It was very loud. Very loud for 15 watts. Didn't over heat. Sounded terrific.
 

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On a tube amp the transformer is looking for what it is rated for. If the resistance is lower it alters the voltage to compensate and the voltage is higher than "spec" so it has to dissipate that through heat so transformer gets hot. If it gets too hot it may or may not blow up. The other way around you are just losing efficiency of the amp. I bet an 8 ohm celestion would sound even better than the 16ohm. The amp tries to match the resistance of the 16 ohm by altering voltage lower in this case IIRC, so you are putting a few watts less output of the amp and the amp is straining a bit to do it.
I like to think of it as using your transformer as an attenuator
 

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Played at the blues jam for three hours straight with no problems. It was very loud. Very loud for 15 watts. Didn't over heat. Sounded terrific.
That is the ultimate test. If you played it that long and it didn't overheat, you're good to go. Not to mention you were paying attention to it*, to notice it if did overheat, so that to me is a pretty good test.

You too can now go on the internet and strongly defend the "mismatch of 2" camp. HNG^%$


*One night I accidentally did a mismatch of 4 - I thought I was plugging into a 16 ohm 412 cab at a practice rental place, so I used the 16 ohm tap on a 15 watt amp. Turns out the cab at the space was mislabeled and was actually 4 ohms. I ran it like that for about an hour, quite loud since I was playing in a full band practice, and I didn't notice until I smelled the amp. It was just about too hot to touch. Turned it off, let it cool down and moved the cab to the 8 ohm tap. Was good for the rest of the night and no long term problems with the amp. That was about 6 years ago.
 

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That is the ultimate test. If you played it that long and it didn't overheat, you're good to go. Not to mention you were paying attention to it*, to notice it if did overheat, so that to me is a pretty good test.

You too can now go on the internet and strongly defend the "mismatch of 2" camp. HNG^%$


*One night I accidentally did a mismatch of 4 - I thought I was plugging into a 16 ohm 412 cab at a practice rental place, so I used the 16 ohm tap on a 15 watt amp. Turns out the cab at the space was mislabeled and was actually 4 ohms. I ran it like that for about an hour, quite loud since I was playing in a full band practice, and I didn't notice until I smelled the amp. It was just about too hot to touch. Turned it off, let it cool down and moved the cab to the 8 ohm tap. Was good for the rest of the night and no long term problems with the amp. That was about 6 years ago.
I played a whole night with a 2 ohm amp into an 8 ohm speaker. It got a little hot, but it didn't kill anything.
 

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I played a whole night with a 2 ohm amp into an 8 ohm speaker. It got a little hot, but it didn't kill anything.
.......and generally 'a little hot' is normal. I think we personify electronics and think, like us, if it gets a bit warm, we better be careful. These things are designed to get hot and dissipate the heat. The big question, of course, is "how hot is too hot?" My amps get hot enough in normal operation to be uncomfortable to touch after three or four hours of playing. As they're supposed to.
 

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The hot that matters is whatever it takes to melt the thin coat of insulation on the wire that forms the coils inside the transformer. Dissolving insulation leads to shorts, and shorts lead to more current passing than is spec'd for, and too much current makes coils behave like fuses...that go "POOF!".
 
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