4 ohm Amp into a 16 ohm cabinet 1x12

[TheWinterSnow]

Didnt read all the stuff here, but if the cab has a higher Indepence (16 in this case). It shouldnt harm. The other way around... you kill it. Our other guitarplayer did this once by accident. Plugged his head into the 4Ohm one instead of the 16Ohm. Think the head was switched to 8 Ohm.

kind of backwards, the general rule for all amps is to not put a lesser load on the output (4ohm cab into a 16 ohm amp), this causes an extra dissipation of heat due to more current flow through the amp and speakers. The generally causes overheating and premature failure. In tubes it changes the bias in a way that can make them too hot and burn out their plates.

With a SS amp they can have massive resistive loads on them including an infinite resistive load (not having a cab connected). If you place more than double the rated load on a OT the residual magnetic field will build up to voltages high enough that would cause the dielectric winding insulation of the OT to break down on the causing high voltage arcs, essentially frying the OT, tubes and possible other parts of the amp, and if you are grounded to the amp (physically touching the ground electrical point), thousands of volts potential through you which will more often than not, kill.

 

[Therion_Prime]

With a SS amp they can have massive resistive loads on them including an infinite resistive load (not having a cab connected). If you place more than double the rated load on a OT the residual magnetic field will build up to voltages high enough that would cause the dielectric winding insulation of the OT to break down on the causing high voltage arcs, essentially frying the OT, tubes and possible other parts of the amp, and if you are grounded to the amp (physically touching the ground electrical point), thousands of volts potential through you which will more often than not, kill.

This I don't get.

With SS you mean solid state, right? But in the next sentence you talk about tubes and OT (output transformer ?). I was under the impression that SS amps have neither?

Can you clarify this please?

 

[John_C]

This I don't get.

With SS you mean solid state, right? But in the next sentence you talk about tubes and OT (output transformer ?). I was under the impression that SS amps have neither?

Can you clarify this please?

solid state, it doesn't matter how big the load is as far as killing it is concerned. However, an output transformer in a tube amp can have a catastrophic failure if you put too high a load on it

 

[TheWinterSnow]

This I don't get.

With SS you mean solid state, right? But in the next sentence you talk about tubes and OT (output transformer ?). I was under the impression that SS amps have neither?

Can you clarify this please?

yes SS = Solid State. SS amps do not have an OT, the reason why tube amps will blow if they don't have a load or an extremely high load on them is becuase of electrical arcing in the OT, since SS don't have an OT, no residual voltages will build up causing the phenomena.

 

[Metaltastic]

yes SS = Solid State. SS amps do not have an OT

Except the Peavey XXL (and maybe others)

 

[slashvanyoung]

Again, the Peavey XXL is a solid state amp, but it HAS a tube amp OT. But it's the only SS amp that I know of that features one.

Edit: Damn, Marcus!

 

[drew_drummer]

...Hot Plates use some kind of dynamic resistance emulation or something now too. They are more than just a big static resistor.

Yeah, they're also a big heatsink!!

 

[TheWinterSnow]

Except the Peavey XXL (and maybe others)

I have read about an amplifier circuit that connects two power transistors in a push pull setup as a tube amp. Considering very low voltages (only up to a ßdc of 20) and the fact that the primary coil is usually a 1:1 in relation to the secondary coil and not a stepdown, there isn't enough power in that amp to cause a total catastrophic OT failure. But if you push the power amp hard enough without a load it still could happen.

The big reason that residual voltage builds up is from the massive voltages required for tubes, a massive amplification factor connected on a larger winding of a transformer. that sets up for a more powerful inductance kick from the transformer, one that can keep voltage sustained.

 

[Full_Tilt]

Reactive loads are a trip, depending on the manufacturing of the speaker, there is a spot in the upper mids (from 1-3K) that has virtually no resistance.

I don't think most read what he said correctly. His amp output is 4 ohms and the cabinet is 16ohms. This means that the cabinet will have a heavier amount of resistance than what the OT is expecting. This is actually a safe way to go for tube amps to a certain degree as the tubes are not put on as much strain (they don't work as hard). Since they don't work as hard the OT stays cooler as well. However if the load is extremely high, the voltage swings inside the OT can cause arcing which will destroy the OT and the tubes, but has to be a pretty high load usually 64+ ohms. 32 ohms is the last safest on a 16 ohm tap, 16ohms is the last safest on an 8 ohm and generally anything up to 4 ohms, and 8 ohms generally shouldn't exceed 8 ohms (but still this is playing real safe, it takes a real high load to cause arcing).

The end result of running a 4 ohm amp into a 16 ohm cab is a reduced output wattage and a slightly darker sound. The tubes would actually last longer and the OT would run a lot cooler, but since you were scared to the point of buying another amp that has a selector, all is good.

Although this post wasn't as relevant as intended im glad I read it . Its a bit more knowledge than I had before

 

[Therion_Prime]

Very interesting stuff in this thread!

One last question:

I read somewhere, that if an amp has a "metal thingie" on the back, it has an output transformer.

I ask, because a valvestate 8100 HAS such a "metal thingie":

True or BS ?

Here are the circuit schematics:

Pre Amp:
http://www.drtube.com/schematics/marshall/pc0689.pdf
Power amp:
http://www.drtube.com/schematics/marshall/pc0689p.pdf

 

[streetwise]

Very interesting stuff in this thread!

One last question:

I read somewhere, that if an amp has a "metal thingie" on the back, it has an output transformer.

I ask, because a valvestate 8100 HAS such a "metal thingie":

True or BS ?

Here are the circuit schematics:

Pre Amp:
http://www.drtube.com/schematics/marshall/pc0689.pdf
Power amp:
http://www.drtube.com/schematics/marshall/pc0689p.pdf

That's the power transformer.

 

[Therion_Prime]

That's the power transformer.

That's what I think, too.