how to keep a variac happy?

If i have a power amp that draws AC from a variac set to 85 volts, is it problematic if the incoming AC from the wall fluctuates from 116-121?
Sorry but isn't that the whole point of the variac? To take variable voltage in and stable voltage out?
If the variac is simply a variac (i.e., an autoformer intended for manual adjustment of AC voltage), for any given setting the output voltage will vary in the same proportion (i.e., by the same percentage) as the input voltage.

Some variacs, however, are contained in instruments which also include mechanisms and circuitry that automatically adjusts their setting such that a stable output voltage is maintained. Although those adjustments, when required, will not be instantaneous, and may be accompanied by a significant amount of mechanical noise.

-- Al
If you are running it at 85 VAC for long periods, I would make sure that it was overspecced by 50%. That is, if you have a 1000 W load, I would use a 1500 W Variac.
It's the outboard variac that comes with and powers Joule Electra amps, specifically the VZN-80. It is supposed to stay at 85 volts during operation. I'm pretty sure it doesn't self-adjust.

I'm wondering if investing in a voltage regulator would help as my Belkin FP60 does reports incoming voltage drops when the stereo is playing and especially when the air conditioning kicks in (drops down to 116). Or even installing a dedicated line for the hifi gear?

The amp and variac are currently out for repair. The variac is shot and a new core is needed, although it might be cheaper to replace it altogether with a commercial product direct from variac corp. anyone have experience with that?
Hello Tort.

I use a dedicated line for every component, so I think that you have a good idea there. Also, I use industrial/medical Variacs and Isolation transformers exclusively. Works for me - and my system is BLACK.