This is for an audio amp. I can do all the calculations and figure the windings and all that jazz but I have another question. When choosing the core do I choose it based on the amps output power or do I choose it based on the total power consumption of the amp. I'm assuming the latter but I just want to make sure because that makes the transformer a whole lot larger and heavier. 100w core has an area of 10 cubic centimeters but a 375w core is nearly twice that at 19.4 cubic centimeters.

So, if I want a 100w amp do I make the transformer for about 375w or just go with the 100w with a margin to prevent core saturation?

Dang. It has been a while.

Best I can remember it would be better to go with the total wattage using a toroidal core for a cleaner output and better capacitance coupling.

If there is a large magnetic field nearby or you are using magnetically sensitive tubes, consider a ferroresonat style core. These are a pain in the ass.

I hope this helps.

Power is conserved in a transformer (minus loss), you're just trading volts for amps & vice versa. A 100W (output) amp is going to consume considerably more than 100W, depending on architecture/components. I assume you know that & that's where the 375W comes in. If so, all components need to be able to handle 375W on the input (power) side.

Perfect, thank you!!

I ran an amplifier through a Kill-a-Watt meter. With all tubes running I was able to get the 100w amp to consume a little over 200w. I'm thinking that 375w gives a good margin even if it may be a bit excessive.

If your test shows a bit over 200W of consumption then you should go with the 375W core. Now to get your wire diameter sized.

quote:

Originally posted by bdavis:
If your test shows a bit over 200W of consumption then you should go with the 375W core. Now to get your wire diameter sized.

375w figures to 3.125A on the primary. So, 17ga should do the trick.

I'm also seeing different charts that list different max amps for the different gauges. One says 18ga is good.

quote:

Originally posted by mark123:

quote:

Originally posted by bdavis:
If your test shows a bit over 200W of consumption then you should go with the 375W core. Now to get your wire diameter sized.

375w figures to 3.125A on the primary. So, 17ga should do the trick.

I'm also seeing different charts that list different max amps for the different gauges. One says 18ga is good.

The differences are likely due to the insulation since that is what will be affected by the heat first...or someones opinion since it likely could go either way. Also, your 375W will almost never be a sustained draw. However, unless the cost difference is great I would go with the larger so you don't fight heat issues.