Are A/V receivers good source for transformers for PSU?

Get 2 microwave oven transformers of approximately the same physical size. Separate the E & I sections (they are not interleaved) by cutting the welds. Remove the secondaries & one of the primaries. Remove some of the turns on that primary & install it on the core with the other primary. Reweld the sections, clamping tightly to avoid an air gap.

The number of turns you'll need to keep can be calculated, but should be checked under power before the reweld.

I just did this to get a 40v @ 10a xformer. Finding one to buy wasn't easy & the prices offended my chea..., er, frugal nature. MOT's are free.

Bob

In order to estimate the transformer specs, you'd need to know the receiver's rated power output. Then you can use the relationship that power P = V^2/R and also P = I^2 * R.

Let's say each channel of the amp is rated at 100 Watts into 8 ohms. To find the RMS voltage the amp is putting out at that rating, you use

V^2 = P*R = 100*8 = 800

V = sqrt(800) = 28.28

But remember that's RMS, so peak is 1.414 times that or 40V. And also remember that you have plus and minus supllies, so 80V total. That's the minimum the transformer is putting out after rectification and filtering. (NOTE that this assumes the specs were on the level... probably true for a decent name-brand receiver, unlikely for a no-name.)

As for the current:

I^2 = P/R = 100/8 = 12.5

I = sqrt(12.5) = 3.53 amps

Again, remember that this is RMS current, so the peak will be 1.414 times higher. However, the RMS is probably the value you really want anyway. Note that if the spec is for N channels driven, you multiply the per-channel current by N.

In the Good Old Days of simple stereo, that would be all you'd need. But modern A/V amps may spec different powers to different channels, so you may have to do some extra calculations and a bit of guesswork.

Best regards,

Bob Masta DAQARTA v4.51 Data AcQuisition And Real-Time Analysis