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I revamped 4 of these little bad boys for a customer recently. The PA is 2 6v6 p-p with a plate voltage of 335v. As an experiment I swapped a Mercury 5E3 OT in and the amp lost a lot of mojo. Less overdrive and squish. Both OTs are physically very similar if not the same size. What could it be about these transformers that is so different? This has really made me believe that transformers REALLY can make a big difference... it's not the placebo effect. I don't think MM is a lesser unit, just different somehow. Maybe the older (40-50 yrs) OT has lost some gauss?
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Do the X-mers have the same impedance ratio? -
The OT is the heart of the amp, bigger and better qualtity laminations, more interleaving etc isnt always better, depends on what you want from the amp,Comment
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Ok so can you explain this? Does more interleaving and better laminations lead to better coupling thus better efficiency, thus cleaner/louder?Originally posted by guitarmike2107 View PostComment
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I wouldn't count on that that. 6v6s can see loads from >10K to 6.6K. It's sort of like having an unlabeled value ceramic capacitor and an unlabeled film capacitor, trying them in the same place in a circuit and concluding "film caps sound better" when in fact the difference has to do with the value of the caps and not their construction. Just my 2c. Then again, it could be the lams, interleaving or something else too....Originally posted by lowell View Post
NathanComment
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Amen, I sure wouldn;t assume they were the same just from the tubes. All I wold assume was that both transformers would work with 6V6s.
Two transformers can have different weight wire, so different DC resistance there. The winding pattern can be different. Transformers work on turns ratios, but the number of turns is not specified. Inductances can differ. Different iron, diferent characteristics.
etc etc.Education is what you're left with after you have forgotten what you have learned.Comment
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Interesting. If that's the case then is it REALLY so imperative that a speaker be the "correct" Z? This leads me to believe it must not be such a hard and fast rule that an 8ohm speaker HAS to be used when the OT is rated for it. It's my understanding that a lesser than rated Z on the secondary stresses the OT while a greater Z stresses the power tubes.Comment
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For the most efficient power transfer, the generator should equal the load.
The generator being the output transformer.
The load being the speaker.
The load is fixed.
The speaker can be substituted.
If the math was to be worked out, it will be apparent that at some load value the power transfer will be optimized.
Any deviation , up or down, from this optimized value will result in less power being transfered.Comment
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But you are assuming some sort of point impedance. What if your tubes are happy with a range of reflected impedance like 3k-10k, and one transformer reflects 3.5k to 7k, and another reflects 6k to 10k? Both make the tubes happy. Both are different. And further, we can talk about efficiency, but this is not a curve like Mt.Everest. A bit to either side of optimal is not that steep a slope.
You want to talk stress on the parts? OK, fine. Calculate exactly how much "stress" is put on a tube or a transformer when for example an 8 ohm speaker is used insted of a 4 ohm. Or the other way around if you like. And more importantly, what form does this stress take?
One SHOULD match the speaker to the impedance tap, sure. But most advice also tells you you won;t hurt a darn thing if you are off by a notch. In other words, plug the 4 ohm load into the 8 ohm tap and no harm results.
This whole thing is like the air pressure in your car tires. It is SUPPOSED to be some amount, maybe 34 pounds. Now more or less than that will stress something. Fine. 33 pounds pressure is a pound low. I am sure we can do some math and find that that missing pound makes my car less efficient. But really, if I am going to drive to Cleveland and back, how much difference will that pound make? Not much. 18 pounds? Well now sure the car will feel mushy and gas milage will suffer, but most anything in the 32-36 psi are will work just fine.
This is just a tube guitar amp, not rocket science.Education is what you're left with after you have forgotten what you have learned.Comment
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