4ohm / 16ohm switch

[Ringhammer]

Well, considering all this, I’ll just make it a 4 ohm cabinet and only use the B25B 2x15” cab with the B25b head.

The idea came from the fact that the B25B cabinet has a 4 ohm / 16 ohm switch from the factory and I was thinking it would be no big deal to emulate that.

 

[Downunderwonder]

Probably for the best.

If you wanted to get fancy you could use 2 jacks and a DPDT switch between that flipped over to partly obscure the opposing jack not in use. Hopefully you would always go for the correct option.

 

[BassmanPaul]

It has always been my understanding that having a cabinet or cabinets that have a lower load than the head (2 ohm cabinet / 4 or 8 ohm head) is bad for the head.

As indeed it would be however all of my amplifiers are stable into a 2Ω load.

 

[Tim Skaggs]

My thought wasn’t switched jacks, but wiring so that one standard 1/4” mono jack would be wired to the speakers in parallel and labeled “4 ohm”, and another, separate 1/4” mono jack would be wired to the speakers in series-parallel and labeled “16 ohm”. This way there is no switch or switched jacks to worry about.

That is a schematic I’d like to see, but otherwise I’ll try to interpret the schematic referenced above and eliminate the switch and just wire the speakers in “A” mode to one jack and “B” mode to the other.

If the B25B could just run in 4 ohm, I wouldn’t bother with all this and I could use it with any cabinet I have...

Can't be done without some way to open up a connection somewhere, otherwise you will be plugging in to a short. Series wiring will have at least one connection between + & - speaker terminals. That connection would have to be opened or removed in some way (switch or switched jack) before the parallel wired jack could be used. Parallel and series wiring can't co-exist in "ready to use" condition. There has to be something that can remove continuity from one or the other wiring configuration so the other one can function.

 

[Downunderwonder]

You know all those threads where the fx loop has crudded up causing dodgy connection and intermittent signal loss? Switching jacks. Not what you want.

 

[Wasnex]

Tube amps have impedance switches on the back and nobody thinks anything about it. When you set up your rig, it's good idea to make sure the switch is in the right position. The same would be true if you installed an impedance switch in a speaker cab.

Several companies make series/parallel boxes. Perhaps one of those would be a good option.

Here's an example that's rated for 400W: Cab-Link - Radial Engineering

 

[coreyfyfe]

I wired a beat up old 2x10 with a series parallel switch like this, having a bunch of tube amps including an SVT and B25 this basically allowed me to cover all my options for a tester cab. I think I used Invalid Link Removed and just soldered to the terminals (removed the screws), I remember it being stupidly over rated for the job.

On my B25 I wired the two taps to separate outputs so I have 8 or 16 ohm options and I would run it either with one 8 ohm cab or two 8 ohm cabs using a palmer cab merger to run them in series.

Like @Wasnex said, I don't really get the hand wringing around the switch here. OP mentions having tube amps with impedance switches and specific ohm requirements. As long as you're checking all of your connections and settings first you should be fine.