If I put a 16Ω speaker on an output transformer that wants to see 8Ω or 4Ω, does it stress the output transformer or the power tubes? And the other way around: do I stress or damage the speaker?
Why don't I notice any problems? Is it because I'm just playing the amp for an hour a week? (and not 5 days a week for 6 hours continuously)
the truth about speaker - output transformer mismatch
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modman
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Intripped
- Cap Cooler
What I know is that there are safe mismatches and not safe mismatches.
Probably also not-so-safe mismatches.
PS: here Dr.Z says something, but still no info about possible speaker damages
Probably also not-so-safe mismatches.
PS: here Dr.Z says something, but still no info about possible speaker damages
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bmxguitarsbmx
- Cap Cooler
The higher reflected impedances have the capability of reflecting much higher voltages across the primary windings of the output transformer and to the plate of the output tubes. Intuitively, it seems like running a higher load would be safer. But, if you look at the loadlines, much higher reflected impedance also generates a much higher plate voltages and much higher interwinding voltage differences. The miracle of magnetics is that you can often still get the full rated power into the 4Ohm load as you can when connecting a 16 ohm load to that same 4 Ohm output. How can that be possible? It is possible because the Plate voltage has increased. SS amps can't do this because they don't have an output transformer to transform the Voltage/Current ratio.
Two examples:
Most Fender OPTs are wound with only 2 layers. Primary and secondary. The chance of arcing between high voltage primary and Ground potential secondary is less. So, you can get away with a lot. Low interleave transformers have lower magnetic coupling coefficients and therefore cannot develop anything close to the theoretical maximum reflected plate voltages.
The Mesa Dual rectifier is an example of an output transformer that has 7 layers. The Primary is interleaved with the secondary to increase magnetic coupling. However, each interleave offers the opportunity of a super high voltage to be next to ground potential, which increases the chances of arcing between windings. Additionally, That increased magnetic coupling allows the reflected voltages to get closer to the theoretical maximum reflected plate voltage. Magnetic coupling is measured as leakage inductance (mesa opt having low leakage inductance compared to Fender). The Mesa DR OPT is a high quality design and is famous for arcing tube sockets and smoking output tubes as well as arcing windings when using 16ohm Marshall cabs on the 8 ohm tap. Early DR's didn't have a 16 ohm tap.
So, it depends.
If you mis-match with higher loads you may get super high plate and interwinding voltages. Hopefully your OPT is underbuilt.
If you under-load, you can get excessive current and suffer overheating. Hopefully your opt is overbuilt.
Another thing to consider is how square the waves are. My 2 cents.
Two examples:
Most Fender OPTs are wound with only 2 layers. Primary and secondary. The chance of arcing between high voltage primary and Ground potential secondary is less. So, you can get away with a lot. Low interleave transformers have lower magnetic coupling coefficients and therefore cannot develop anything close to the theoretical maximum reflected plate voltages.
The Mesa Dual rectifier is an example of an output transformer that has 7 layers. The Primary is interleaved with the secondary to increase magnetic coupling. However, each interleave offers the opportunity of a super high voltage to be next to ground potential, which increases the chances of arcing between windings. Additionally, That increased magnetic coupling allows the reflected voltages to get closer to the theoretical maximum reflected plate voltage. Magnetic coupling is measured as leakage inductance (mesa opt having low leakage inductance compared to Fender). The Mesa DR OPT is a high quality design and is famous for arcing tube sockets and smoking output tubes as well as arcing windings when using 16ohm Marshall cabs on the 8 ohm tap. Early DR's didn't have a 16 ohm tap.
So, it depends.
If you mis-match with higher loads you may get super high plate and interwinding voltages. Hopefully your OPT is underbuilt.
If you under-load, you can get excessive current and suffer overheating. Hopefully your opt is overbuilt.
Another thing to consider is how square the waves are. My 2 cents.
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bmxguitarsbmx
- Cap Cooler
I didn't address which parts are stressed the most.
1)The speaker doesn't care.
2)You will most likely smoke your output tubes are possibly arc your tube sockets and even need to replace your screen resistors and grid stoppers.
3)Lastly, you might arc your OPT. Isolation between interleaves is typically at minimum 3000V between primary and secondary. Even for Mesa DR's it seems to be arced tube sockets and replacement of grid stoppers and screens r's. That stuff must be replaced to protect the power tube and the OPT.
1)The speaker doesn't care.
2)You will most likely smoke your output tubes are possibly arc your tube sockets and even need to replace your screen resistors and grid stoppers.
3)Lastly, you might arc your OPT. Isolation between interleaves is typically at minimum 3000V between primary and secondary. Even for Mesa DR's it seems to be arced tube sockets and replacement of grid stoppers and screens r's. That stuff must be replaced to protect the power tube and the OPT.