BF Bassman OT swap for more options?

[JSett]

I was thinking the other day about my BF Bassman head and the fact that I'm slightly restricted with the options of only 4 or 8 ohm cabs. Often I'm gigging at places with kitshare going on and, here in the UK, a lot of them are setup at 16ohm. There's a lot of Orange cabs and Marshalls laying around, as well as homebrews and it's pretty popular for them to be 16ohm...which means I can't use my amp without also lugging a cab around with me.

So, seeing as it's already not unmolested (MV in the back), would it be a solid idea to put in an output transformer that can do 4/8/16? Like this Hammond one?

I was thinking either drill an extra hole and have 3 dedicated outputs or put 1 master output and have a on/on/on switch in the other speaker orifice?

Good idea? Bad idea? From what I can tell it'd be a relatively easy thing to do and not particularly expensive...unless I'm missing something obvious with the fact that OT is an 8ohm primary and I'm guessing the amp is 4ohm? Would that require any specific extra changes internally?

[sal paradise]

Out of interest, what’s wrong with using 16ohms apart from power reduction?

[JSett]

Out of interest, what’s wrong with using 16ohms apart from power reduction?

Well, the Bassman is set for 4 so going as high as 16 will a) probably sound like trash and b) possibly fry the transformer by drawing too much voltage.

Tube amps are normally okay one step either direction but 2 steps is not good. Solid state are the ones that you can go as low as you like but just lose volume.

[sal paradise]

Out of interest, what’s wrong with using 16ohms apart from power reduction?

Well, the Bassman is set for 4 so going as high as 16 will a) probably sound like trash and b) possibly fry the transformer by drawing too much voltage.

Tube amps are normally okay one step either direction but 2 steps is not good. Solid state are the ones that you can go as low as you like but just lose volume.

Ah yes, I was thinking about hifi stuff which is mostly ss.

So it’s unused power being sent back to the amp again?*

*this is the limit of my technical knowledge- I can’t believe I actually started an audio engineering/electronics degree when I was 19. I lasted 3 months until logarithms came in- still don’t even understand how they work. Me & numbers are not friends, especially counterintuitive things like ohms.

[JSett]

No I think it's literally just too much voltage being drawn through the transformer to supply the higher load*

*My knowledge is all internet-gleened and spotty at best.

[redchapterjubilee]

I had a Mercury magnetics 2/4/8 output transformer installed in my tweed Bassman Ltd chassis in a headshell for this reason. I wanted access to a better selection of attenuator /load box and they all seemed to be 8 ohms. I don’t think the amp sounds any different.

[MayTheFuzzBeWithYou]

Can‘t contribute much except for: yes: one step is okay, two is too much! The other thing is only valid for transistor Amps and could really damage your tube amp.

But as I would like to use my Bandmaster more I‘m piggy-backing on to this question to learn more about this topic!

[Dr Tony Balls]

Hammond 1760L. Direct drop in, and i'd wire one speaker jack to the 16Ω secondary, and the other to either the 4Ω or 8Ω one (your choice).

EDIT: OR build yourself an impedance matching box. But that's extra kit.

[JSett]

Hammond 1760L. Direct drop in, and i'd wire one speaker jack to the 16Ω secondary, and the other to either the 4Ω or 8Ω one (your choice).

EDIT: OR build yourself an impedance matching box. But that's extra kit.

Yeah the 1760L was the one I'd lined up. Theoretically does that mean I could have the 4Ω connected up and use that for 4Ω and 8Ω loads and the other to 16Ω?

[Dr Tony Balls]

Hammond 1760L. Direct drop in, and i'd wire one speaker jack to the 16Ω secondary, and the other to either the 4Ω or 8Ω one (your choice).

EDIT: OR build yourself an impedance matching box. But that's extra kit.

Yeah the 1760L was the one I'd lined up. Theoretically does that mean I could have the 4Ω connected up and use that for 4Ω and 8Ω loads and the other to 16Ω?

Yes, BUT not at the same time. Alternately, if there's room you could maybe put a rotary switch in one jack hole and use it as an impedance selector.

[JSett]

Yes, BUT not at the same time.

Oh, for sure, I know better than to do that

Alternately, if there's room you could maybe put a rotary switch in one jack hole and use it as an impedance selector.

That's a very good idea, and I like a good solid (foolproof) system!

I'm off to order some parts

[marqueemoon]

I thought this is part of what the pedal/pedalboard power amp was intended to address.

[JSett]

I thought this is part of what the pedal/pedalboard power amp was intended to address.

Covering all bases

[JSett]

I thought this is part of what the pedal/pedalboard power amp was intended to address.

Actually, I wanted to come back and elaborate on this. The Pedal/poweramp situation was to address the times I might have to get to a gig on public transport*. Most of the time the three of us travel up in a car (with limited space) together...on these occasions the ability to use any cab laying around that's part of the evenings kitshare/house equipment is a massive benefit as I can just leave my cab at home and just sling my guitar, pedals and amp head in the car and off we trot.

*although, at the moment the Ballsmom is mostly getting use as a bass preamp at home

[JSett]

Hammond OT and impedance rotary both on order. I have a gig in a couple of weeks so hopefully I can get it set up ready to go before then.