Amp into cab with greater load

[tomjackson]

Is it safe to run my Princeton reverb 8ohm speaker output into a 16ohm cab?
It says on the back 4 ohm minimum but it doesn't say not to run it at 16, just that it's a 8ohm output.

[Twinfan]

It's an 8ohm output, but it allows a 4ohm minimum?  Sounds unusual.

If that's the case though, it should be fine.

[tomjackson]

Sorry, I'm wrong, it says 8 ohm min.

The manual says you you can add a 16 ohm extension cab if you change the internal speaker to 16ohm (it's currently 8) but they are just parallel outputs.

But you think 16 will be okay?

[jpfamps]

Valve amps should be run into their rated load.

Running a valve amp into too high a load can and does result in damage to the output transformer and/or the power valves.

You may get away with running a Princeton into 16 ohms, but it's safer not to.

In my opinion valve amps sound best when they are connected to the correct load.

[tomjackson]

Thanks for the replies.

The problem is it sounds so good running throughh 2 celestion golds!

But advice taken, from what ive read the trannies on the reissues are a bit weedy anyway.....

[Frank]

Sorry, I'm wrong, it says 8 ohm min.

The manual says you you can add a 16 ohm extension cab if you change the internal speaker to 16ohm (it's currently 8) but they are just parallel outputs.

That's because two 16 ohm speakers in parallel gives you an 8 ohm load. For reasons I won't go into, an 8 ohm in parallel with 16 ohm gives you a 5.333 ohm load, you could probably get away with using that if the amp has a 4 ohm output.

In related matters, if the amp has seperate output jacks for 16, 8, 4 ohms then don't ever think it's ok to use two at the same time. That's really asking for trouble.

[jpfamps]

In related matters, if the amp has seperate output jacks for 16, 8, 4 ohms then don't ever think it's ok to use two at the same time. That's really asking for trouble.

That information wrong.

It is perfectly safe to use say the 8 and 4 ohm taps simultaneously as long as you use a load rated at twice the impedance of each tap, ie a 16 ohm load on the 8 ohm tap and an 8 ohm load on the 4 ohm tap.

Each tap reflects twice the nominal loading to the valves in parallel, so the correct load is presented.

If you want a more authoritative discourse on this, as opposed to post on an internet forum, then you can consult the Radiotron Designers Handbook, 4th Edition, pages 200-203.

[dave_mc]

^ seriously? I must remember that. I have a ton of speaker cabs at different impedances and that knowledge would let me run some together for teh lulz. :)

[Frank]

In related matters, if the amp has seperate output jacks for 16, 8, 4 ohms then don't ever think it's ok to use two at the same time. That's really asking for trouble.

That information wrong.

It is perfectly safe to use say the 8 and 4 ohm taps simultaneously as long as you use a load rated at twice the impedance of each tap, ie a 16 ohm load on the 8 ohm tap and an 8 ohm load on the 4 ohm tap.

Each tap reflects twice the nominal loading to the valves in parallel, so the correct load is presented.

If you want a more authoritative discourse on this, as opposed to post on an internet forum, then you can consult the Radiotron Designers Handbook, 4th Edition, pages 200-203.

You got me! Fig 5.8 on page 203 of the RDH. I was aware of that but I think people get confused enough with speaker matching so I was really trying to gloss over that way of connecting cabs.

[jpfamps]

You got me! Fig 5.8 on page 203 of the RDH. I was aware of that but I think people get confused enough with speaker matching so I was really trying to gloss over that way of connecting cabs.

Indeed they do, and as most people seem to have enough trouble connecting the correct load to that amp at the best of times, to avoid confusion, I don't recommend this.

[Frank]

to avoid confusion, I don't recommend this.

The best solution is always the simplest. The two speaker trick makes sense when you think about it as two double loads in parallel but the safest option is to tell people not to do it. It saves a lot of tears and replacement tubes.

[dave_mc]

yeah but that means no lulz  :x

just to clarify that I've got the right end of the stick, say i have a 16 ohm cab/speaker and an 8 ohm cab/speaker, it'll work if I plug the 16 ohm cab/speaker into the 8 ohm jack on the amp, and the 8 ohm cab/speaker into the 4 ohm jack on the amp?

I *need* to hear what my copperhead sounds like combined with my texas heat, dangit! :lol:

[Frank]

Yup, that's the ticket. What the man said.

Each tap reflects twice the nominal loading to the valves in parallel, so the correct load is presented.

Twice the loading, but paralleled so it amounts to half of twice the loading. If that makes sense.

... and the other thing the man said

to avoid confusion, I don't recommend this.

[Frank]

Just to further muddy the waters, always bear in mind that a speaker rated 8 ohms nominal impedance isn't 8 ohms at all frequencies. If you're in the habit of tuning down or playing baritone guitar then your 8 ohm driver may be presenting a very different load from the rated value. Proceed with caution, watch for the transformer getting hot and don't cane the volume until you're convinced that the amp's happy to run with the mixed load.

[dave_mc]

thanks :)