running amp and cab with different ohms

[adamcbest]

i have a mark iv head at 8 ohms and a 5150 cab at 16 ohms.. will i have any problems running them together for like an hour to test the amp??.. I'm still waiting for my mesa cab to arrive

[Algiman]

Don't Do It!!!!

While you'll probably get away with it for a short time, the strain on the output transformer could prove to be a very expensive mistake.

[adamcbest]

the mark iv manual says that mismatching is ok but it will shorten the life of the tubes.. i was planning on putting in JJ 6L6's soon anyway, so i figured that wasn't a big deal

[Paul Secondino]

IT wont hurt the amp at all. It'
s okay to go into a cab with higher impedence. IT is bad to go into a cab with too low an impedence.IF you went into a 4 ohm cabinet, you would have a problem for sure.

THe way it works is that if you go into a 16 ohm cab, your amp will have to work a little harder to to get to a specific volume as it would have to if oyu plugged into a 8ohm cab. It will work the tubes more but it wont damage the output transformer.

[Gresh]

Paul is right, you can only mismatch impedence in one direction. As long as the speaker is of equal or higher impedence than the amp, you're safe.

[JESTER700]

With solid state amps you're OK going to a higher impedance - though going lower than designed may result in thermal overload or amp cookery.

But with TUBES you should MATCH the impedance! Tube amps have output transformers designed to drive a certain impedance or range. Going lower works the tubes, but going higher can damage the output transformer. Now, at low volume for an hour with a 1:2 or 2:1 mismatch shouldn't hurt, but I wouldn't push it...

[JESTER700]

More here...

http://aga.rru.com/FAQs/general.html#imp-1

[Algiman]

Absolutely. Going lower you'll get away with for a short time, though it isn't a good idea. Going higher is definately out - and replacing the output stages of an amp is expensive!