Apart from the blatant copyright violation, how's the circuit? Did anybody try it?
There are even better ones published in Elektor. I didn't try them, so I speak from studying the circuits and articles.
Once I prepared an amp design I sorted out all turn-on delay circuit for inrush-current limiting I could find. I remember having settled for something that uses a 12V aux supply to drive the relay. Assuming that there is a low-voltage supply available in a big amp anyway one can use much smaller, much cheaper components and go for safer and more reliable circuits than the above (it has relatively high power losses which let the components fail quicker, and it poses a relatively big mains voltage"surface area" inside the amp to touch, accidentally).
The schematic I'm talking about can be found in the same Elektor audio circuits special edition as the circuit "by" Promitheus, it was part of a complex amplifier schematic. I don't have it around. But I've drawn a board layout sketch for it: a flat power relay (the horizontal mounting type) with five power resistors in parallel over it's top and some passives nearby, 1" by 1" surface area, under 10 Euro, fits on most aux power supply boards easily.
I didn't keep the sketch. And I didn't build the board, sorry.
But to answer the actual question: The circuit should work, as Elektor refers to it sometimes still today (it's more than ten years old). And for practical experiences, why not ask the inventor: Promitheus
PS: In an integrated amp, there should be a separate power supply for the low power circuit parts. And in some commercial amps, I've even seen a separate standby transformer that was also used to supply the relais. That's why I argued for using a 12V aux supply. I can't tell if that applies to everybody's todayish gainclone, of course.
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