Reasons for transistor failure

[Jon Snell]

If RS, Farnell or Mouser do not have them, they are either obsolete or old stock and probably no good for a new build but when needs must, there are a few reliable sources on fleabay. Look at the feedback and how long the seller has been with fleabay.
Ensure your chosen supplier is based in the same country as you are. That will ensure you are covered by any warranty for the replacement of faulty goods.
Don't forget, with fleabay, there is a moneyback guarantee from PayPal, use it for faulty/damaged goods and the seller is responsible for the return postage.
If you are not professional, you may have trouble proving your components are faulty and you didn't cause the 'fault' but it is possible as most sellers do their best to help.

[Mick Bailey]

For all parts in current production I use RS, CPC, and Farnell. Sometimes though I have little choice other than to scour Ebay for certain parts and I have a number of reliable sellers both here in the UK and overseas that I buy from that specialize in obsolete parts. I buy certain transistors and many tubes from Ukraine, Bulgaria and the Czech Republic without any problem. Some Chinese suppliers I've used have also been good for some difficult to find ICs and these have been genuine NOS and worked just fine.

I wrote up my findings on fake/defective PT2399 ICs some years ago and this caused some reliable and honest suppliers to take a look at their stock and they found that their own supplies had been infiltrated.