MPSH10 & KSP10

[XXL]

These transistors are baffling me. iv seen this transistors mounted on top of each other to add more power out. like in the output of many 300mw tx's, there will be like 5 of these in a row. but when I try to replace them with any other transistors, maybe like the 2n2222a, it doesn't work. I make sure the pinouts are the same as well.

only these 2 transistors mentioned seem to stack.

Is it maybe because the bias is then off because its a different transistor, or is it the transistor doesn't work the same way ?

[Krakatoa]

The trick is in the internal capacitances of the semiconductor junctions. In the 2N2222 they are a lot higher than that of the ksp10, when paralleling they add up and input - output matching and tuning gets totally off.
There is a chance that using a similar transistor like the BF199, BF240, S9018... will work

[Albert H]

I used to use a pair of BF199s when I needed a bit more power than I could get from a single one.

[XXL]

does anyone know of an equivalent for these transistors ? they're both obsolete now

[Albert H]

I use BF240 and BF199. I also have about 4000 BF494 "lock-fit" transistors in our warehouse. They're (quite closely) equivalent to the BF199, but are slightly weird to insert into PCBs because of their peculiar legs. I had to buy an adaptor for our "Panasert" PCB loader!

[Zozo]

does anyone know of an equivalent for these transistors ? they're both obsolete now

Not sure the MPSH10 is obsolete as it pops up in homebrewing circuits all the time in the RSGB's monthly Radcom. Anyhow a quick eBay search still gives many results. I've just popped down to the workshop and have at least 2000 of this little blighters manufactured by Fairchild.

[Bton-FM]

does anyone know of an equivalent for these transistors ? they're both obsolete now

Not sure the MPSH10 is obsolete as it pops up in homebrewing circuits all the time in the RSGB's monthly Radcom. Anyhow a quick eBay search still gives many results. I've just popped down to the workshop and have at least 2000 of this little blighters manufactured by Fairchild.

The MMBTH10 (MPSH10 equivalent) only just went obsolete so they can still be obtained easily. On AliExpress they are less than a penny each.

I think the reason a lot of people still use the MPSH10s in their transmitters is because they are using the same old design from yeeeeears ago...

[teckniqs]

There was loads of them cheap on eBay a while back like packs of 1000 for a fiver!
....I think people just use them because they are so cheap and even put like 3 or 4 of them together to use as a cheap output for a few hundred mW. I've not looked on eBay but there's probably still loads of them "new old stock" cheap on there in huge bulks.

[Bton-FM]

There was loads of them cheap on eBay a while back like packs of 1000 for a fiver!
....I think people just use them because they are so cheap and even put like 3 or 4 of them together to use as a cheap output for a few hundred mW. I've not looked on eBay but there's probably still loads of them "new old stock" cheap on there in huge bulks.

Yeah you're right they are still easy to come by.