Ohm challenged

[Aaronharmon]

I never thought about this before, but I am running a single pair of YJ EL84s in my RM100. Do I need to half the ohms on either the amp or cab since I am only running a single pair of tubes?

I have a RA412XLT

Please be as specific is possible in your answer. As the title says, I'm not at all knowledgeable with regards to impedance.

Thanks,

Aaron

 

[JKD]

If you are only running two tubes in the amp then yes, you need to halve the ohms on the amp.

If you're running into the 16Ohms Mono input on the cab, the amp should be set to 8Ohms.

 

[Aaronharmon]

You the man, thanks a million.

Just out of curiosity, what if I didn't do that? How could it affect my tone, my amp, my cab, etc?

I know that Ohms are a measure of impedance, but what difference does it make. Why don't they just make all cabs 8 Ohms for example?

 

[JKD]

I won't pretend to fully understand this but when the amplifier is matched to a given load via it's output circuit (tubes and transformer) it'll be operating at it's most efficient...frequencies are amplified correctly and passed through to the speakers as designed.

When you don't match the load, all sorts of stuff can happen...one I can remember is there can be signal reflections...imagine water flowing through a big wide pipe suddenly interfacing with a narrow one to try and get the picture. or vice versa.

Output voltage swings and current are relatively high (compared to a guitar input signal) and if the current is flowing into the speaker, it's going somewhere in the amp....

The end result can be as minor as not hearing the signal correctly, increased wear on components or as major as the output failing spectacularly (components overheating, failing, melting, catching fire etc*) and you really don't want the output transformer to die....it's the most expensive piece of iron in the amp usually.


* Most amps have some form of fuse protection when stuff starts to die so that dangerous over-currents/fires seem to be the exception.