Step-up transformer for Amp

[strangedata]

Hello everyone,

I have a full tube amp that I bought in Germany and now I'd like to use it in the US. It's 220V, so I need an step-up transformer to use it here. Currently I'm using a 750VA 110-to-220V transformer, but I feel it's really overkill (not to mention OVERSIZED )

I don't know how many Watts its power source drains, but I used a meter to find out how many Amperes it uses. I connected it to a 220V outlet and found out that it's using 0.15A of current.

The thing is, I'm not sure if 220*0.15 converts to 33W. I know that there's this thing called power factor that I should take into consideration when calculating power in an alternated current circuit, but I'm not sure what it should be for a tube amp.

So, is a 50W step-up transformer enough?

Cheers!

[Dave]

strangedata,

I'm sorry I haven't replied to this post. As you can see no one really uses the forum on my site. I appreciate you stopping by and going as far as registering.

As far as your question, your calculations are correct. 50w will be plenty. It will have enough headroom of power to cover power factor once a load is put on the amp. What is the tube configuration of your amp? 6L6's? KT's?

[strangedata]

Hey Dave,

Thanks for answering!

The preamp uses 2 ECC83 and the power amp, 2 EL84.

Someone told me that I actually should shoot to 70W, but I find it a bit excessive. They took in consideration not only the tubes, but also the heaters.

Anyway, I thought that whatever is inside, the current I measured should cover it all, right?

Oh, and I must say that I really like your site. Hopefully the forum will pick up as well.

Cheers!

[Dave]

Ok, I think I got confused here. You will need a transformer capable of handling more than the total power consumption of your amp not the amp's RMS output. See, I have a Marshall JCM 900. It's a 25w/50w combo. Even though the amp's output is 50w, it's power consumption is 175w. That's with 110/120V @ 3A or 220/240V @ 1.5A. So my transformer needs to cover more than 175w to maintain steady power to my amp. So around a 350w step up transformer would suffice... although providing more than enough wattage in the transformer will provide for more headroom.

[strangedata]

Hmm, interesting... 175W for your combo?

Do you think that the current I measured at 220V (0.15A) is to low?

Cheers!

[Dave]

What you are confusing is the difference between power consumption and RMS output. I have a 50w RMS output Marshall amp whose power consumption is 175w. It takes 175w of AC voltage to produces 50w RMS output of tube driven power. That's why we see less total wattage output than actual power consumption because we are converting AC power into DC power for the vaccum tubes to operate on. Don't ask me to get into all that because I'm not exactly sure how the equations equal out. Tube amps take in AC and step up the voltage to like 400+ DC. Anyways, I think that's what is confusing you is RMS output and power consumption. You can use my figures because 33w is close to 50w. So get you a 300w+ step up transformer and it should be more than enough to provide your amp the necessary wattage to keep the power consumption at a steady consistent rate.

[strangedata]

Hi,

I'm not confusing the output with the input. My output is actually 15W.

Those 33W I figured out by measuring the current going into the amp directly from the outlet (by measuring the electromagnetic field generated.)

What I was afraid, actually, was the so called power factor, since what I measured was a mean current, and not the peaks. Since there must be peaks where the current and the voltage will eventually max out to more than 33W, I thought that maybe someone could tell me what the power factor was.

I ended up using google translator to access the vendors forum (a Russian vendor named Yerasov). On these forums someone calculated a 70W peak... I'll get a 100W transformer, just in case

[Dave]

Wiki says the power factor is the following:

AC power flow has the three components: real power (P), measured in watts (W); apparent power (S), measured in volt-amperes (VA); and reactive power (Q), measured in reactive volt-amperes (var).

The power factor is defined as: P/S

With that being said it can't be too much higher than what the RMS output is. So I'd say 70w peak is a pretty safe figure to use. 100w transformer should work just fine.

[strangedata]

Alright!

Thanks a lot Dave!

Now I'll see if I can find some Seven Star's TC-100 converter around here.

Cheers!

[Dave]

Quick google search shows those aren't that expensive at all. I need me a step up transformer as well but not for an amp...