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12v inverter query

PostPosted: Mon Mar 29, 2010 3:12 pm
by maxx england
Does anyone know about running an amp off a car battery via an inverter? I'd like to be able to use the Hacker valve amp independent of mains supply. It's a nominal 7w, but it's old and well engineered, so it may well soak up a lot more energy.

Re: 12v inverter query

PostPosted: Mon Mar 29, 2010 3:55 pm
by ricochet
It probably draws something in the neighborhood of 60W.

Re: 12v inverter query

PostPosted: Mon Mar 29, 2010 4:25 pm
by jeffl
ricochet wrote:It probably draws something in the neighborhood of 60W.
How would that compare to an Xbox or a laptop?

Re: 12v inverter query

PostPosted: Mon Mar 29, 2010 4:34 pm
by ricochet
http://www.hardcoreware.net/reviews/review-356-2.htm

I'm taking a WAG on that amp's draw. I'll try to remember to look at the sticker on the back of my Valve Junior when I get home.

Re: 12v inverter query

PostPosted: Tue Mar 30, 2010 8:40 am
by maxx england
Did you remember? No hurry, but I'm curious about this one.

Re: 12v inverter query

PostPosted: Tue Mar 30, 2010 11:49 pm
by ricochet
No I didn't, but I just went and looked. The label on the back of my Valve Junior combo says it's power consumption is 35W. It only has a 12AX7 and an EL84 in it. If your little amp has a tube rectifier, that'll add a bit more. A 2A heater at 5V is 10W. my 60W WAG was generous.

Re: 12v inverter query

PostPosted: Wed Mar 31, 2010 9:16 am
by maxx england
Found a tech discussion which reckons the valves are the same as the Cavalier model, so 2x ECL86, 1 x EZ80.

There's no unseemly crackling or humming from the amp, which appears to be a very good sign from the limited surfing I've done. There's going to be jack sockets fitted soon so I can run a 12" Celestion off it. :twisted:

Re: 12v inverter query

PostPosted: Wed Mar 31, 2010 10:58 am
by Buffalo_Bill
It's rated 7 watts, so it draws 7 watts. What is it about 7 watts you don't believe?
The power inverter might use up more energy than 7 watts. You should be OK for hours using a bike or lawn mower battery.
Bill

Re: 12v inverter query

PostPosted: Wed Mar 31, 2010 11:02 am
by maxx england
As a technical innocent, I thought it wisest to find out what I can and can't do (on the old engineering principle of measure twice, cut once). So, as I understand now, the sound producing side will need only 7w to run, but the power delivery will be slightly higher. It looks very much as if I am now in a position to terrorise yet more innocent eardrums.

Thank you.

ps

Aahhaahhhaaahahaaahhhhaaa :twisted:

Sorry, just slipped back into the old ways, happens, you know.....

Re: 12v inverter query

PostPosted: Wed Mar 31, 2010 4:20 pm
by ricochet
The power output of any amp is always less than its input. The heaters of the tubes (valves) in a tube amp always draw a good bit more power than the amp's output. That was and is one of the most important advantages of solid state amplification, transistors don't have heaters to waste power.

Re: 12v inverter query

PostPosted: Sat Apr 03, 2010 1:40 am
by michaelm
If you want to run any audio equipment from an inverter, it's best if you can Try Before You Buy. As you seem to have discovered, be sure that the power (watts) rating for the inverter is greater than the power draw of the load.

I live off the grid and get all of my AC juice from inverters. In my experience, the ones sold as 'modified sine wave', which are actually modified square wave, can produce totally unacceptable hum in any sort of audio equipment, including PC speaker systems. Good quality pure sine wave inverters work great. In fact, the juice that they produce in many cases is probably cleaner than what we get from the grid.

Good luck and HTH.

Re: 12v inverter query

PostPosted: Sat Apr 03, 2010 9:25 am
by maxx england
That's pretty much cleared it up. I can use a low wattage (150 +/-) inverter but it must be pure sine, not fake.

Thanks everybody. Now I have to find a cheap one :mrgreen: