Has anyone used the RD70HVF1's from Hong Kong being sold on Ebay? A few sellers have them, they're between £15 and £20 each. Was wondering what peoples' experiences have been with them. "Genuine" ones seem to be a little more expensive than this.

I've tried the fake RD15HVF1 fets before without any problems. Managed to get almost 30w out of it, but they don't seem to be as rugged as the originals.

That sounds encouraging, thanks. I have one real RD70 left... if this one doesn't survive my clumsiness I might see how the Chinese ones bear up.

Just out of interest, what voltage and drive level were you thrashing that poor RD15 with!?

Counterfeit stuff that isn't at a ridiculously good to be true price is usually OK if you add a bit of extra thermal capacity and just go easy on the wick.

It's in their interest to avoid being found out, so that they can continue to sell hundreds of thousands of devices, as opposed to 5 on eBay. Nowadays I'd go as far as saying that they do a pretty decent job.

A few years ago, I designed part of a variable current source/sink with some IRF1310N FETs. We made a few hundred of them so ordered about 500 devices as there was a bulk discount at that quantity. No idea where from, purchasing sorted that.
They all worked fine, dissipated more or less the required amount of power and handled the voltages it was supposed to. I only found out that they were counterfeit after I'd left the company and held onto the FETs as they didn't want them. I was using one in a switching power supply I was repairing, at what I thought was well within the continuous avalanche engery spec. I suspect they were very good counterfeits, however I don't think I'll ever know.

Here is how do China based manufacturers work...
Imagine yourself as Mitsubishi. You order batch of 100000 pieces of RD15 from chinese factory. Factory makes 150000 pieces (costs are so low that actually customer pays for production of all 150000 pcs) and 50000 do not meet standards. Customer gets 100000 pieces of standard, good, fets. Factory sells 50000 bad pieces for less than standard price but enough to enchance production. In next batch, customers fets are same or worse than pieces that do not meet standard. Still, factory sells new enchanced pieces for cheap because someone else paid for production and they get them for free.