Finding replacement transistors

[fjalvingh]

Hi all,

I am trying to repair a HP 8656B which has trouble on the low frequencies - the low frequency loop is unlocked. I found at least one problem: one transistor in the PLL phase detection circuitry has blown. This is a 2N4209 which seems to be hard to get - so I need to find a replacement... To test I just replaced it (and its brother which form a pair in the schematic) by a 2n3906, and this does solve the problem: the pll locks and I can again select proper frequencies.
But that 2n3906 is way slower than the original, so I would like a replacement that is a bit more close to its specs. The transistor seems to be used mostly as a fast switching transistor.

And that brings me to the real question.. How to find such a replacement? I did the usual Google dances and looked at Mouser, but I do not seem to be able to select the things I would like (this 2n4209 has 10..15ns turn on and rise time, and that is way less than the 2n3906)..

Are there other online resources that I can use to find something like this?

Thanks for your help!

Regards,

Frits

[bdunham7]

If it works at all with 2N3906 it should be fine with the purported replacement from Central Semi, the CM4209....if you can find it.  Don't be too proud to scrounge a few units off of eBay, I see numerous sellers with 2N4209s for not too much money.

[tepalia02]

This one seems to be close : https://www.ebay.com/itm/255028370686

[fjalvingh]

Thank you both for your answers, but there is another thing I would like to know: how to find a replacement type, i.e. another transistor having fast on/off time. Is there any tooling for that? How do you select a component type by the specs you require?

[bdunham7]

Thank you both for your answers, but there is another thing I would like to know: how to find a replacement type, i.e. another transistor having fast on/off time. Is there any tooling for that? How do you select a component type by the specs you require?

There are such tools, but they aren't magic.  Figuring out what your requirements are and then doing a parametric search in Mouser or DigiKey is probably a better use of your time.  Or just asking here.  But here are two 'cross-reference' tools you can look at.

https://www.onsemi.com/products/product-services/competitor-cross-reference

https://alltransistors.com/crsearch.php

[kripton2035]

↓ Type   Code   Mat   Struct   Pc   Vcb   Vce   Veb   Ic   Tj   Ft   Cc   Hfe   Caps
2N4209      Si   PNP   0.3   15   15   4   0.05   200   850   3   50   TO18
BC291A      Si   PNP   0.36   45   45   6   0.2   200         100   TO18
BC291B      Si   PNP   0.36   45   45   6   0.2   200         150   TO18
BC292A      Si   PNP   0.36   45   45   6   0.2   200         100   TO18
BC292B      Si   PNP   0.36   45   45   6   0.2   200         150   TO18
MM4209A      Si   PNP   0.36   15   15   4   0.2   200   850   3   50   TO18
NTE106      Si   PNP   0.36   15   15   4.5   0.2   200   850   2   50   TO18