Same Amp but 3 different speaker ohm outputs?

[Avraxas]

Hello all!

Looking at this Mullard 3.3 Schematic: http://www.r-type.org/articles/art-003h.htm I read that you can choose what ohm speaker output your can have just by adding a specific resistor value.

And makes me wonder if i can add a rotary switch with 3 different Resistor values in my AC4 (head) i want to build https://el34world.com/Forum/index.php?topic=32165.0, so i can choose an output (4ohm, 8ohm or 16ohm) according to a cabinet I have available.

What is your opinion?

Thank you.

[Latole]

I don't know .

[Merlin]

Looking at this Mullard 3.3 Schematic: http://www.r-type.org/articles/art-003h.htm I read that you can choose what ohm speaker output your can have just by adding a specific resistor value.

It's telling you what feedback factor to use depending on the output transformer tap you are using, but the transformer still needs to have the right tap for the speaker impedance. Plenty of OTs have 8 & 16 ohm taps so you can still add a switch for those if you like.

[pdf64]

... I read that you can choose what ohm speaker output your can have just by adding a specific resistor value. ..

I think you've misunderstood.
R4 is the NFB shunt resistor.
Its value just matches the power amp gain to the NFB ratio, so that the amp works as intended which OT secondary wiring arrangement and nominal load impedance has been used.

And anyway, Vox don't use NFB :)

[Avraxas]

Thank you very much!

Just read about NFB.