Didn't blow up my amp today

[Jacew]

Re: Didn't blow up my amp today

yes and no, you dont want to go too low on a tube amp. an 8 ohm ot tap doesnt want to see a 2 ohm load on even a good amp for long. the power tubes will suffer since its the relationship between speaker and tubes the ot is dealing with. you are 100% correct on a ss amp, you dont want to go low since the amp may see it as a short and give up the smoke but higher is ok. youll just get less power. 99.9% of the time, its best to match things properly

I thought that obvious from earlier posts in this thread, but good to point out.

You should always use matching impedance in tube amps in general, but it's safer to go lower than higher if you can't.

[jeremy]

Re: Didn't blow up my amp today

yes and no, you dont want to go too low on a tube amp. an 8 ohm ot tap doesnt want to see a 2 ohm load on even a good amp for long. the power tubes will suffer since its the relationship between speaker and tubes the ot is dealing with. you are 100% correct on a ss amp, you dont want to go low since the amp may see it as a short and give up the smoke but higher is ok. youll just get less power. 99.9% of the time, its best to match things properly

[Jacew]

Re: Didn't blow up my amp today

As a rule of thumb:

You can safely use higher impedance speakers with SS amp no problem, but lose lot of power important for SS amps. Which is what I think was referred in original post.

With tube amp you want to use lower impedance speakers for the reasons JamesPaul very well explained above.

[JamesPaul]

Re: Didn't blow up my amp today

Lugged my second 4x12 into my rehearsal space today and hooked it up. Amp is an EVH 5153, early serial. Forgot to switch the output selector over from 16 to 8. Played for 10 - 15 minutes or so before auddenly realising my mistake. Switch the amp off, set it to 8 ohm out, turned back on. Played for another hour. Output tranny seems fine - no smoke, no smell, no horrifyingly loud silence. Guess I dodged a potentially very expensive bullet.

My only questions is... why? Conventional wisdom says you can connect a speaker load with higher impedance than the output and you'll be fine (I've tried it before - there's some tone suck but that's pretty much it) but shouldn't connect a lower load to the amp lest you'll send it to amp heaven.

Review the Maximum Power Transfer Theorem. If the amp internal impedance and the load (speaker) impedance do not match, the amplifier dissipates the excess power not reaching the speaker.

It is actually the inverse scenario of what you describe.

When the speaker impedance is lower than what the amp is set for, it is the tubes dissipating the excess power. This is harder on your tubes.

When the speaker impedance is higher than what the amp is set for, it is the transformer dissipating the excess power. This is harder on the transformer and the transformer runs a hotter.

I avoid mismatching as I have never noticed any improvement in tone. Still many people and even some manufacturers will tell you a mismatch of one tap (16 ohm to 8 ohm, 8 ohm to 16 ohm, 8 ohm to 4 ohm or 4 ohm to 8 ohm) will not damage your amp. This has to do with impedance varying with frequency. Also manufacturers over-engineering the transformer size for a safety factor.

What kills transformers is no speaker load. This is the case of speaker impedance being much higher than what the amp is set for. Actually an infinite ohm speaker. In this case all the power is dissipating in the transformer. This is why you never run a tube amp without a speaker load.

[Jack_TriPpEr]

Re: Didn't blow up my amp today

... I never thought 10 minutes or so would kill an amp, though.

+1

[Mincer]

Re: Didn't blow up my amp today

I think it really depends on the design of the amp. Some amps don't tolerate mismatches well, and tubes will wear faster. Some do (my Mesa does) and you can use mismatches to change the tone. I never thought 10 minutes or so would kill an amp, though.

[Coma]

Lugged my second 4x12 into my rehearsal space today and hooked it up. Amp is an EVH 5153, early serial. Forgot to switch the output selector over from 16 to 8. Played for 10 - 15 minutes or so before auddenly realising my mistake. Switch the amp off, set it to 8 ohm out, turned back on. Played for another hour. Output tranny seems fine - no smoke, no smell, no horrifyingly loud silence. Guess I dodged a potentially very expensive bullet.

My only questions is... why? Conventional wisdom says you can connect a speaker load with higher impedance than the output and you'll be fine (I've tried it before - there's some tone suck but that's pretty much it) but shouldn't connect a lower load to the amp lest you'll send it to amp heaven.