Question asked a million times`

[Simonski]

But i always forget.

Is it ok to run and 8ohm head into a 16ohm cab?

[crushing day]

yes, just don't run an 8 ohm head into a 4 ohm cab

[Some Bozo]

Think of it like the impedence of the cab is what's stopping the amp trying to run at infinite power....too little impedance and the magic smoke escapes from your amp

[hamo]

Think of it like the impedence of the cab is what's stopping the amp trying to run at infinite power....too little impedance and the magic smoke escapes from your amp

So for an amp/electricity noob like myself: say each ohm from the amp is a runner, and each ohm in the cab is a blocker, then you need at least one blocker for every runner. It's okay to have more blockers than runners, but not vice versa.

Bonus super noob question: could I use my solid state Marshall combo as a cab if I bought a tube head? Or is that just dumb/not possible.

[Ears]

Depends on the amp doesn't it? on its class of operation and also remember transistors react differently to valves.
An infinite impedance (open cct or even just very high) will make short work of a valve amp's output transformer.
In fact, for tube amps just connecting (but not playing it) into lower than rated impedance is unlikely to damage it but just act of turning it on when it's open circuited (too high) is inviting trouble.
edited to correct my inherent dsylexai

[rocklander]

Think of it like the impedence of the cab is what's stopping the amp trying to run at infinite power....too little impedance and the magic smoke escapes from your amp

So for an amp/electricity noob like myself: say each ohm from the amp is a runner, and each ohm in the cab is a blocker, then you need at least one blocker for every runner. It's okay to have more blockers than runners, but not vice versa.

right.. well, no completely wrong, but in effect right.
the amp wants a bunch of electrons to run from the signal out to ground. if there's nothing stopping it then the electro0nicsy bits will dump all it possibly can to the point that the electronicsy bits over heat (from all them electrons running to ground). the impedance (of the speaker) literally impedes their way to ground, slowing it down therefore the eletronicsy bits (in the amp)don't get so hot they die.

if you put a straight piece of wire from the positive of a car battery terminal to the negative, the wire wont last long and present some significant bang and light show, but if you have something with a bunch o' resistance (resistance is DC, impedance is AC) then it will all glow and stuff, but not die (depending on the resistance blah blah)

Bonus super noob question: could I use my solid state Marshall combo as a cab if I bought a tube head? Or is that just dumb/not possible.

the speaker part yes, but you couldn't take the output of a head and put it into the input of your combo (too much signal at the front end).. well I guess you could.. but not for long

[Some Bozo]

if you put a straight piece of wire from the positive of a car battery terminal to the negative, the wire wont last long and present some significant bang and light show

They used to do exactly that at my old work ( making power rectifiers ) to test the connecting bits and pieces to destruction.

[RobRoyMcCoy]

Without getting into any technical discussion at all, we recently did an experiment where we had three different valve amps (a 4 watt, an 8 watt and a 15 watt) and we ran them all at their correct impendance match e.g. 8 ohm transformer tap into an 8 ohm speaker. It is useful to note that we designed the amplifiers to operate optimally into 8 ohms.

We then ran them all into a 16 ohm speaker at up to maximum power for a moderate length of time (say 10 minutes each amp). Whilst the amplifiers did not blow up during these tests, we struggled to get a really good clean and overdriven tone out of any of them when they were mis-matched. When we put them back, the magic returned. This is obviously a subjective opinion but we were certainly convinced.

YMMV.

Rob

[hamo]

Bonus super noob question: could I use my solid state Marshall combo as a cab if I bought a tube head? Or is that just dumb/not possible.

the speaker part yes, but you couldn't take the output of a head and put it into the input of your combo (too much signal at the front end).. well I guess you could.. but not for long

I feel unjustifiably proud of myself for at least realising that much.

[Simonski]

thanks guys. Its one of those things thats best to check before you do it

[tubeswell]

In most cases it generally won't hurt to run a tube amp 1 'knotch' above or below the rated impedance of the output transformer. The OT is a device that merely 'reflects' a load resistance back to the tubes that are driving it, and most output tubes can tolerate a range of load resistances within a certain band. e.g. a 6L6 can run on 3k2 or 6k6 or anywhere in between, a 6V6 can run comfortably between 4k and 10k. However the load resistance (in combination with the bias and screen and plate voltages) does affect the tonal characteristics of the tube and the power output. All other things being equal, a 6V6 running into a 4k load resistance will not put out as much power as it would running into 8k (but it will sound more compressed). What you don't want is to run the the tubes without a load resistance, or run the load resistance too high (as infinite load resistance has the same destructive effect on the tube as no load resistance at all). JM2CW

[Scooter13]

DREDGE! To avoid hitting the new thread button.

My Cuba St Radiotone 5W has a speaker out on it, which is unlabelled. The speaker inside is a 4 Ohm 8" Weber ( I think its 4 ohms, i can't remember the model number written on it). I really wanna try this mighty little growler of an amp in to a larger speaker/s, but I only got 16 ohm cabs. I know it's generally ok to mismatch 1 step up, but what about 2 steps? i.e. 4 Ohm amp in to 16 Ohm cab (I've read sometimes this is too great a step up and bad stuff can happen)?

I'm assuming the Radiotone's speaker will be disabled when I plug in to the speaker-out jack?

If this is too dangerous, and I don't wanna hurt the wee bugger...could I daisy chain two 16 ohm cabs, effectively making an 8 ohm load for the amp to see? But that = 6 speakers connected to a 5W amp, a 2x12 and a 4x12.

[willow13]

If this is too dangerous, and I don't wanna hurt the wee bugger...could I daisy chain two 16 ohm cabs, effectively making an 8 ohm load for the amp to see? But that = 6 speakers connected to a 5W amp, a 2x12 and a 4x12.

I'm sure one of the guru's will chime in...but i'm gonna say stacking the 2 cabs for 8ohms should be ok. Have you tested the "speaker out" to make sure it is 4ohms??

[RuBear]

Just rewire one of your 16 Ohm cabs to a 4 Ohm, doable with either your 2x12 or 4x12.

[MogwaiBoy]

Going with the "up one notch, but not down" theory, it should be safe to run an 8 om head into a 16 ohm cab, but not 4 into a 16 I think. As stated - you should be able to rewire the 16 ohm cab to be 4 ohm, or even have a 4/16 (parallel/series) switch installed. I've done this before, makes the cab more versatile

Even the cab extension jack on my Laney Cub 10 says "8-16 ohm output" even though the internal speaker is 8 ohm - so that's basically Laney saying it's fine do go up a notch. Whether is sounds as good as matching ohms, is upto you! At the very least it will cut some power/volume off the capability of the amp. Ryan will be able to explain the science of that.