In general an autoformer rated at 220V in but with 120V in it will be able to put out 0-120V out.....
Thanks, Granger. That's what I needed to _know_. I could intuit that, but I don't trust my lay-person knowledge of electron behavior. I will change the plug and receptacle for conventional 120v configuration and use, and keep an eye out for dusty old tube amps. I can meter the output manually during use.