ohm question

[Fritz6]

Do I have this right?: When selecting cab get one wired for the lowest load the amp can take, since this will let the head put out maximum power?

But since my 5150 is 120 watts and the cab has 4 G12H30's (total 120 watts), should I get the cab wired at 16 ohms to knock down the juice hitting the speakers a bit? Will the head perform less efficiently seeing 16 rather than 4 ohms?

I'll be going into a Hotplate so the speakers won't be getting hit full on anyway, but I always wondered if a head has a "favorite" ohm setting and about the sound difference (if any) between ohm settings.

 

[That90'sGuy]

Re: ohm question

120w is a lot of power. Ohms provides the resistance to the electrical current. If I were you I would check the amp to see specifically what ohm cabinets it supports and whatever the highest one is listed, I would use that ohmed cabinet.

On my Triamp, it's 100w. However, with my 16ohm cabinet, it gets knocked down to 80w. This is very useful for me and maybe it will be for you (if you have to crank it to get the best tones).

 

[Artie]

Re: ohm question

You really shouldn't think of speaker load as a power control mechanism. The speaker load just determines the ratio of voltage to current that you're asking your amp to supply.

For instance, you could have 100 watts with all of these:

100 volts/1 amp
10 volts/10 amps
1 volt/100 amps

When you lower the load, you raise the current. But that doesn't necessarily mean that the amp can push the extra voltage - or that it will be good for it.

On a tube amp, you're simply selecting the "tap" off the output transformer that matches your cab. So, you're selecting the amount of current that the OT will supply. Everything within the amp will be pretty much the same. In other words, its still a 120 watt amp.

 

[Fritz6]

Re: ohm question

Would this mean that the tap off the OT increases and decreases as the volume is raised or lowered? Because if it's constant wouldn't there never be a danger of blowing speakers?

So with my 5150 on 10 into a 16 ohm cab, the cab will only get hit with 100 watts because of the cabs higher resistance?