I'm refurbishing a SX-1250 and wish to confirm the proper transistor replacements on the AWM-091 protection board. The service manual specifies Q4 is a 2SC945A-Q (2SC1647-P) and Q5 is a 2SC1166-Y (2SC1384-Q). From an old posting by Mark, I find:

" There would be a few more parts for beefing up/renewing the protection circuits...

two: Q4, Q5 522‑ZTX1056A NPN TO‑92E ebc 150v 3a 1w (Vce(sat)=0.3v @ 3a) 120mhz 30‑1200 hfe relay driver transistor
one: Q6 (2sc1166 50v, .2a .6w) 512‑KSC2682YSTU to‑126 ecb 180v .1a 1.2/8w 200mhz 100‑320hfe $0.31 ea
one: C4 100uf/16v (100/35) 647‑UPW1V101MPD $0.15 protection circuit timing capacitor
one: C3 4.7uf/25v (4.7/50) 647‑UPW1H4R7MDD $0.23 protection circuit ac power on signal integrator
two: C5,C6 100uf/50v (100/50) 647‑UPW1H101MPD $0.50 protection circuit voltage regulator
two: C1,C2 470uf/6v (470/16) 647‑UPW1C471MPD $0.52 protection audio input caps "


Here he specifies Q4 and Q5 get replaced with the same Mouser part number.
Is this correct?

Thank you in advance, Udo

Yes, the ztx-1056a when still available can be used for both positions.

The Q5 position carries 30 - 50 mA relay current continuously, thus the Collector to emitter saturation voltage should be as low as possible to minimize heating. The ztx-1056a is well suited for this.

The Q4 position is subject to high pulse discharge currents upon shutdown or protection disconnection, and the ztx-1056a has a very high pulse current rating as well.

But due to the low quantities sold, our favorite distributors are no longer renewing stock and making them a special order item, which then requires orgers in huge (to us) quantities.

Thus I will need to find suitable individual replacements - not hard - just annoying.

The ztx-1056a is / was a mighty-mouse of transistors - lots of gain, lots of current, lots of voltage and a low Vcesat to boot....

Hello Mark, Was hoping you'd see this. Got a few of these last order, so I'm set. Just wanted to be sure to not screw this project up.
Thank you, Udo

Just remember that the layout of the leads is ebc and the lettering is on the OPPOSITE, ROUNDED side, not the FLAT reference face for the lead layout.

So look at it with the FLAT face facing you, with the leads pointing down
Then the leads are E - B - C left to right.

It even tripped me up the first time.....