Can I Use a Powerstat (Variac) in an Attenuator?

[CynicalMan]

I have a used Powerstat variable autotransformer, similar to a Variac. I'd like to know if it could be used in an attenuator, either on its own, or like the tapped transformer in something like a power brake.




It's DC resistance is around 14 ohms, so it could be use with a 16 ohm output. Is this possible and has anyone done anything like this?

[zachomega]

DC resistance is only one element of what may or may not make it suitable.  There is inductance as well which changes rather drastically as you tap the transformer.  Also, that resistance I assume is from end to end of the coil, so as you tap it, you will have notably less resistance. 

My first instinct is going to be to say no, but I'll wait for somebody with a bit more knowledge to pipe up. 

-Zach

[R.G.]

Sure it can be used in an attenuator. What's not certain is whether it will do what you want.

Some observations.

It may have a wire resistance of 14 ohms, but it has an inductance which is huge compared to a speaker. At a guess, juggling some numbers, the primary of that thing looks like a 14 ohm resistor in series with a 14 Henry inductor, and that in parallel with whatever load is attached to the output as transformed by the transformer action. The inductance is so huge to keep it from drawing too much current for the primary alone when doing the job it was designed for. Unless there is a secondary load attached to it, it is likely that it will cause some ugliness when attached to an amp directly. It will make any transient spikes much worse, make a feedback amp prone to oscillation, and have an impedance that varies - a lot!

Not all amps will oscillate, not all will die from transient spikes.

But it will need some work to get it to sound good.

It's possible - but maybe not a promising place to start.

[wavley]

That thing might be better used to get the EVH Brown Sound 

I've often though of trying to diy something like this https://taweber.powweb.com/weber/mass.htm Maybe not with all the eq, but the speaker motor and balanced out would be nice.

That was good thinking on the variac, it seems to make sense but I tend to agree with the others, it is most likely not going to sound good.