Ohm Mismatch Issue

[devouredremains]

Yesterday I lent my 1960a to a friend so he could try the cab out before he purchased one himself. When he disconnected the cab to return it to me he noticed he had the speaker cable plugged into the 4 ohm input on the cabinet. He was running his head at 16 ohms and is worried that some damages may have occured although the head still functioned after the mismatch. He told me he ran it this way for about 20-30 minutes.

I had him bring the head over with the cab so I could look over it. I removed the chassis and checked the tubes and fuse for discoloration and both were fine. The amp still powers up correctly and produces sound.

Is he in the clear? Did he somehow luck out or will there now be underlying problems?

 

[colonel kurtz]

he'll be fine

the head was running expecting to see 16 ohms of resistance, but there was really 4...it's sort of equivalent to picking up something you think is gonna be really heavy, but it's not, and you're like "hey awesome, this is easier than i thought it would be"

now if the head was set 4 and the cab to 16, he'd have issues on his hand, because the head would be running full-tilt, and the power would "bottleneck" through either the power or output transformer as a result of the larger than expected rate of resistance

 

[nuclearass]

he'll be fine

the head was running expecting to see 16 ohms of resistance, but there was really 4...it's sort of equivalent to picking up something you think is gonna be really heavy, but it's not, and you're like "hey awesome, this is easier than i thought it would be"

now if the head was set 4 and the cab to 16, he'd have issues on his hand, because the head would be running full-tilt, and the power would "bottleneck" through either the power or output transformer as a result of the larger than expected rate of resistance

BTW...With some amps (maybe even most amps) the safe mismatch is the other way around...

This sure as hell seems to be a debated issue in the net. Best way is to avoid mismatches and if that's not possible, you should check the manual if it has information on which way the mismatch is safe. (See for example mesa dual rec manual).

 

[AdamWathan]

Yeah colonel kurtz has it backwards... If the cab is set to 4ohms and the head is at 16ohms, then the cabinet is trying to draw MORE power from the head because there is less resistance which is what will damage the output transformer. You should be okay though, I wouldn't worry about it. These things aren't pieces of crystal glassware, they can handle a few mistakes here and there. Usually when you fuck an amp up because of a resistance matchup and something actually goes wrong, it's reaaaaally fuckin' obvious, so if you're saying that you aren't noticing any change, you're golden.

 

[Metaltastic]

Yeah, everything I've heard (operative word there) says that the danger is your situation, Devoured, and running an amp at 4 ohms into a 16 ohm speaker cab just makes it sound choked but isn't damaging. But as F0RBIDDEN said, I think you'd know if there was a problem, so I guess don't sweat it!

 

[devouredremains]

Thanks guys. He will be happy to hear that everything should be ok as it's his first tube amp and was just recently purchased. I tried to do a bit of research on the topic and as nuclear said it's very debated. Everything I read was conflicting. I found a post on another forum where someone had a similar similar mismatch and emailed peavey on the subject and posted the reply he received and it stated this:

Hello Lee,

The amp is designed to use a 16 ohm speaker, and that is what is
recommended.
You can use an 8 ohm speaker, but the amp will run a little hotter and
your
headroom will be reduced, along with slightly reduced tube life.


Regards,
Roger Crimm
Regional Service Manager
Peavey Electronics

So while the amp in question was not a peavey it completely threw me off. Everything I read was conflicting. Thanks again for the info guys. Once again, it's just more proof that the sneap forum is where the most knowledgeable converge.