ZTX450 / ZTX 550 Replacement Question

[SRMcGee]

Folks:

A dumb question, perhaps, but I'm a newbie and am unsure of myself. I need to replace the ZTX450 and ZTX550 transistors in my Pass Labs Aleph P but don't have any on hand. However, I do have plenty of 2N3904 and 2N3906 transistors. I've looked at the datasheets but frankly don't know how to assess whether they are suitable substitutes for the '450s and '550s in this circuit.

Can someone tell me (a) if they are a good choice for this task and, if you can explain it as though you were talking to a total idiot, (b) what I should be comparing on the datasheets?

Thank you!

Regards,
Scott

[SRMcGee]

Folks:

I should also note that I will receive some BC546 and BC556 transistors soon and could use them instead, if they are a better fit for this application.

Thanks for the advice!

Regards,
Scott

[lawbadman]

I'v got the same question.

Can any of these transistors also work instead of ZTX450:
MPSA42
MPSA05
2N5089

[h_a]

The zetex are really not that special parts; they excel in maximum collector current and maximum power dissipation, so they are sturdy parts. But that is ususally not needed, so use whatever part has sufficient voltage and current rating. That's nearly every TO-92 bjt, except low noise parts that usually have a little low voltage ratings.

Have fun, Hannes

[Spooky Electric]

Just be careful not to mistake the collector and emitter pin when changing from ztx to bc parts. The "round side" of the transistor's body is different.

[SRMcGee]

Hannes and Floyd42Flake:

Thank you for your responses! I can figure out the proper orientation, but don't know whether the voltage and current ratings for the BC546 / BC556 or 2N3904 / 2N3906 transistors are adequately sized to replace the ZTX450 / ZTX550 transistors in an Aleph P. The circuit operates on 60 VDC (and my power supplies are producing that voltage +/- 1 VDC).

I don't know how to read the schematic to figure out the current or voltage demands on the transistors, or to determine from the datasheets whether any of these replacement parts are suitable. What should I be looking for?

Many thanks,
Scott

[mjf]

hello.
ztx450/550:
volt rating 45v..........current rating 1a or so........power rating 1w.... and hfe(current gain) around 100..........
but i think in the ccs (of the aleph p) transistors with lower current- and power rating will work...........
mpsa42/92, bc637/638, bc639/640, bc546/556, 2n3904/3906.........should work.
if you are not shure you can ask that question in the pass labs forum too......
greetings