using 4ohms or 16ohms is there a difference ?

[Melodyman]

When did Marshall start including 4 ohm taps on their output transformers? The earliest JTM45s had 8 and 16 ohm and 100 volt taps.

Marshall used to have 4 output/speaker jacks in the back of the Super Lead 100w amps in the later 60's .. I never tried to power 4 16ohm cabs with one head, but they added this feature so you could and as a result the 4ohm tap needed to use 4 4x12 16ohm cabs.

Does Running 16 ohms on the amp into an 8 ohm cab cause any amp damage? How about 8 ohms on the amp into a 16ohm cab?
What are the risks? How long does it take to cause damage if so?
Thanx..

 

[Jonathan Wilder]

Marshall used to have 4 output/speaker jacks in the back of the Super Lead 100w amps in the later 60's .. I never tried to power 4 16ohm cabs with one head, but they added this feature so you could and as a result the 4ohm tap needed to use 4 4x12 16ohm cabs.

Does Running 16 ohms on the amp into an 8 ohm cab cause any amp damage? How about 8 ohms on the amp into a 16ohm cab?
What are the risks? How long does it take to cause damage if so?
Thanx..

Yes, and yes.

Running a lower load than what the amp is set for (setting the amp for 16 ohms while running an 8 ohm cab) cuts the load that the valves see in half, which allows the valves to go overcurrent, which will burn up an OT quicker than shit.

Running a higher load than what the amp is set for (setting the amp for 8 ohms while running a 16 ohm cab) DOUBLES the load that the valves see. This increases your screen current, since the electron current will see the screen as the easier path. Also causes an increase in flyback voltage that valves don't like.

I don't understand why anyone would want to run mismatched impedance. The ability to match the amp's impedance to the impedance of the cab is there for a reason, and it's not a tonal one. It's there for electrical reasons and is one of those electrical things that shouldn't be played with and should be used as it was intended to be used, not for a "tone tweak".

Bottom line, match your impedance!!!

 

[Purgasound]

I never tried to power 4 16ohm cabs with one head, but they added this feature so you could and as a result the 4ohm tap needed to use 4 4x12 16ohm cabs.

OR just one 4 ohm cab...
OR two 8 ohm cabs...


as for your other question, don't mismatch. Mismatching impedance makes amp go bye bye. At least that's the simplest way to put it.

 

[Sir Don]

Can't say I've noticed any difference in sound with either 4 or 16 ohm output myself.