240 - 110V converters/transformers?

[Spud]

Question for those in the know.

I have just bought a Roadking combo from a US source.

I assume (being a US spec Boogie), it will come 110V format, not switchable between 110V/240V?

I therefore assume that I will need a stepdown transformer with a US socket for this amp.

My question is, why do all the US amps I see on ebay come with a 1000 watt transformer?

Surely if the amps output is 'only' 120 watts, given the stepdown diversity, a 250 watt output supply would be enough??? Or am I missing something?

I can buy a 250 watt transformer from a local store for about $80.00 (£45.00). A 1000 watt version will be twice that + postage and a week to get here :shock:

Any help would be appreciated.

Andy.

 

[Jaroslav]

Well, 120 W is the output power rating, right? Have a look near the place where the cable leaves the chassis, there you have the real power consumption printed. My rackmount DR takes 4 A at 120 V, that means I need at least a 4*120=480 W transformer. So a 500 VA transformer or autotransformer is a minimum for me. It will be similar with yours RK.

 

[Rich M]

The output power is only part of what needs to be fed. I forget the efficiency of AB power amps, but it is <100% (~60-70% IIRC). You also need to power the heaters of all the tubes, supply power to the preamp tubes, indicator lights. Every power resistor in that amp is dissipating some amount of juice. Add to that, a margin of safety, as a transformer will run REAL hot at rated power and you'll see that a 250VA xformer will not work too well.

 

[Spud]

Thanks guy's.

As nobody had replied to my question, I bought an 800watt tranny last week.

Still waiting for the RK to arrive

 

[Jaroslav]

Nobody answered your question? Have you read through the replies? It was written in there, only maybe in a not very obvious way...800 W will be fine.