Pass x250 always on:how much more $ in electricity

The cost per kWH should be available from your power utility company for you to calculate the estimated $$. You might find this rate in your regular billing from them as well.
For eg: if the cost per kilo Watt Hour (kWH) = 10 cents and if your Pass is turn on 24/7 and it is rated at say 250 watt, the formulae that I will use is;
250W/1000W x 10 cents (per kWH) x 24 hours per day x 365 days per year = $219.00 or approx. $18.25 per month.
This is close to what Danlib1 has estimated as well...
Good luck.

I agree with the $20.00 per month estimate. According to Pass' specs, it idles at 270 watts. Running 24/7 is about 200 kwh extra a month....figure on Con Ed hitting you up for a dime average per kwh.

BTW, when I first ran my Class A mono's during the winter, my electric bill increased by $20-25 per month but my heating costs went down. The amps were in the same room as the thermostat!

Jeff Rowland told me that basically you take the wpc and divide by 2. He said running a 150wpc amp {my model 10 } was like leaving on a 75 watt light bulb. Don't know if that applies to other amps or not.

It could very well be that 24/7 operation with a Class A biased amp like the X250 is ultimately cheaper than turning them on and off, as the amps will be much less likely to break and require expensive repair. Keeping the amps on 24/7 means that they will not experience the relatively severe thermal cycles that occur with Class A amps when they are turned on an off. The heating up and cooling down that occurs when you turn a component on and off wears down internal componentry because they expand and contract as a function of the temperature (the most frequent analogy is what the winters do to highways in the Northeast), all the more so with a Class A biased amp, because they run relatively hot when they're on. Running X-600's or X-1000's continuously would likely cost a fortune in electricity (and make for damn hot listening rooms), but if your X-250's only burn 270 watts each, it's probably smart to just leave them on.

I'd love to run my Class A biased VAC monoblocks 24/7, but it would prematurely kill the output tubes.