Re: [EE] Buying semiconductors on eBay

At 11:12 AM 2026-03-25, you wrote:
>I am rebuilding a power supply and I want a 3 to 5 amp regulator in TO-3
>can.
>The LM338K looks right.
>The major distributors like Digikeyare asking three figure sums from them
>which is beyond my wallet.
>On eBay Uk sourced ones are asking  seven or eight pounds but Chinese
>vendors are offering them at prices like five for a pound.
>
>I assume that the  Digikey ones are genuine and that the Chinese ones are
>fakes.  But what are the chances of a UK sourced one being fake?

Hi, David:-

Pretty high I would say, if they're not coming directly from a franchised
distie. Hard to find and obsolete semis are _risky_ buys. I would buy them
if I was in China with free returns (and would dissect one).

Have you considered using a linear regulator controller eg. MIC515x and a
fat MOSFET in a slightly more modern package such as TO-247? ... or even
a TOLL package eg. IPLU300N04S4-R8 ?   JLC will sell 5 pcs aluminum core
single layer  PCB for $18 plus shipping (as low as $3) so SMT is not really
out of reach if you have a way to solder it. That SMT MOSFET claims 200W
maximum dissipation if you can hold the case to 100=B0C.

I guess they used the LM338K in some military and =

industrial stuff (even in the crappy
steel TO-3)- hence the prices- but all the linear =

open-frame power supplies I looked at
back in the day used a circuit with BJT pass transistors like 2N3055
(also frequently fake these days, but real TO-3 ones are only a few dollars=
).
Probably used the almost equally antediluvian LM723 as a controller.

Eg.

https://internationalpower.com/wp-content/uploads/2018/01/IHD15-6.pdf



Best regards,
Spehro Pefhany







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