Single Recto speaker inputs

[crisis]

I have two 4 ohm cabs. A Marshall 1960 and a home made 2x12 with a Geenback and a V30. Both have 4 ohm inputs. Am I able to hook these up to the two 4 ohm outputs in my Single Rectifier?

 

[94Tremoverb]

Not really. The total load will be 2 ohms, which - although it probably won't blow the transformer or do any other harm to the amp, Mesas are tough and not particularly sensitive to mismatches - will be very hard on the tubes, and probably won't sound good. If you're only playing at low volume it isn't a major problem though, it's only a serious issue if you crank it.

The best thing to do is either to make a 'series cable' or series splitter box and run both at 8 ohms, or to rewire the 2x12" to 16 ohms and run both again at 8 ohms (you'll need some means of splitting the cable, again - unless the 2x12" has a daisy-chain output).

 

[rocknroll9225]

no. rectifiers (as well as most guitar amps, really) cannot handle a 2 ohm load, which is what using two 4 ohm cabs together would be. you can only use 2 cabs together if theyre both 8 ohms or both 16 ohms. it is true that mesa amps are pretty insensitive to impedance mismatches, but this still is not the best of ideas.

 

[94Tremoverb]

no. rectifiers (as well as most guitar amps, really) cannot handle a 2 ohm load

This isn't true. All of the old Fender amps (Twin Reverb etc) with 4-ohm outputs were purposely designed to handle a 2-ohm load when an extension cab is connected, and most other amps with a 4-ohm setting will handle it just fine, at least until you reach full power. It's a myth that tube amps can't handle low loads - they will almost all be OK with between half and double the correct impedance, and there's nothing special about 2 ohms from a 4-ohm amp, it's exactly the same as running an 8-ohm cab from a 16-ohm amp for example. It just sounds scary because there are no 2-ohm cabs (apart from the '59 Bassman and Super Reverb combo speakers, that I know of). It really doesn't do any harm other than stressing the power tubes, and then only if the amp is cranked. If the amp is running clean (or with preamp distortion only) the load really isn't critical at all.

but this still is not the best of ideas.

I agree, but it's nowhere near as bad as is often made out.

 

[MrMarkIII]

Do it!
Do it!
Do it!

 

[crisis]

Cheers guys. I was only wondering what it would sound like. Doubt I could be bothered lugging two cabs to band camp and gigs anyway.

 

[erectifier]

they will almost all be OK with between half and double the correct impedance.

I thought this was only true for solid state amplifiers?

 

[94Tremoverb]

I thought this was only true for solid state amplifiers?

No, absolutely not! Solid-state amps have a *minimum* impedance that you must not go under, or you'll fry the output transistors in short order. Although to be strictly accurate, as long as you're not cranking the amp even that doesn't apply, but you must be *very* careful - so don't try it!

Tube amps have a *matching* impedance which is where the most power and best frequency response occurs, and where the highest proportion of the power is transferred to the load.

Tube amps can be safely mismatched in either direction by at least up to a factor of two in almost all cases. There are a few exceptions, where the transformer ratios are already at the outer end of the ideal range (old Marshalls for example), but Mesa amps are not among them - they are not very impedance-sensitive at all, and the worst that will happen is that you'll shorten the tube life a bit and it might not sound very good. It's really not a good idea to run a 4-ohm amp into 16 ohms or vice versa if you're cranking the amp, but 4 into 8, 8 into 4, 4 into 2 etc is all safe. If you're not running the amp above halfway it doesn't even matter *at all* - there just isn't enough power, voltage or current being generated to harm anything even if it's not quite all going where it's intended.