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wmgwizard

wmgwizard

Addicted Member
I am trying to learn how to select replacement/substitute transistors, could someone please verify my choices or suggest more suitable replacements.

All the substitute/replacements are On Semi items from Mouser.

2SB536 (BCE)becomes MJE350(ECB)

2SD381 (BCE) becomes MJE340(ECB)

2SA818 (EBC)becomes MJE15031(BCE)

2SA1628 (EBC)becomes MJE15030 (BCE)

I understand the "pin out" may not match so caution needs to be used during installation. Can I trust the diagram silk screened onto the pc board ?

Thanks to everyone for their continued support, this place is the greatest.
 
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My advice is look up user echowars and mark the fixer these guys seem to be the authority for subbing transistors. I make a point of keeping all good transistors on anything I scrap and it has paid off hundreds of times.
 
Never trust silk screen for pin outs. When you remove the transistor make note of the pins vs the silk screen. If you can follow the trace, compare the next component to the schematic to identify the pins. You can also find the base through diode testing.

Easiest method is an Atlas DCA55.
 
wmgwizard said:
2SB536 (BCE)becomes MJE350(ECB)

2SD381 (BCE) becomes MJE340(ECB)

2SA818 (EBC)becomes MJE15031(BCE)

2SA1628 (EBC)becomes MJE15030 (BCE)
Click to expand...
Do not replace TO-220's with TO-126's.

Actually, it looks like you swapped the replacements...

2SB536 - MJE15031
2SD381 - MJE15030
2SA818 - MJE350
2SC1628 - MJE340
 
@ EchoWars : quote "Do not replace TO-220's with TO-126's."

Why not, what are the potential issues ?

Are you referring to the 340/350 pair ?

What would you recommend in their place ?

Thanks to all for your help.
 
OK...how about: "Do not replace a high-power device with a medium power device".

The 2SB536 & 2SD381 are TO-220, a high-power device. The 340/350 are TO-126, a medium-power device.

The 2SA818 and 2SC1628 are TO-202, a medium power device.

For reliability's sake, replace high-power with high-power, medium-power with medium-power (or high-power if the specs show you're not giving up something you need), and low-power devices with low-power devices (or if the low-power device is being asked to run anywhere near it's limits, replace with a medium-power device).
 
Thanks EchoWars, please appreciate that I asked so I could learn, I was not trying to be disrespectful.

So essentially the larger the transistor the higher it's potential power handling capability, makes sense.

Could you recommend a substitute for the 340/350 set ?
 
There's no universal substitute...the proper sub depends on what the original transistor is doing in the circuit, and how that circuit is arranged on the PC board.

First things first...look up the specs for the original. Many Japanese transistor specs have been compiled here: http://www.audiokarma.org/forums/showthread.php?p=1655960

I will say that if this is for the amplifier driver and pre-driver stage, that I like the Toshiba 2SA1837 and 2SC4793 (TO-220)(Digikey), and the Sanyo 2SA1209 and 2SC2911 (TO-126)(B&D Enterprises). The Toshiba's are fully encapsulated, so if the metal tab is used in your application for electrical conduction to the collector, you'll have to look at some of the On-Semi devices (like the MJE15032/33).

Another issue is that the original 2SA818 and 2SC1628 devices are center-base parts, and most new stuff is center-collector. If the holes in the PC board are arranged in a circle, then no sweat. If they are arranged in a tight row, then subbing a center-collector part for a center-base part gets tricky.

Maybe you are beginning to see that there's 1,000 pitfalls to swapping out original devices with subs. Too many things to consider to simply say 'yeah, swap out your 2SCxxxx with a MJExxxx'.
 
If you are working on the 950, as you stated in another thread, my recommendations above are good ones (the Toshiba and Sanyo devices). With the TO-126 devices, Pioneer arranges the PC board holes on a circle, so installing the center-collector part isn't a problem.
 
I realize that all the specifications are important, but the reality is that exact matches generally do not exist.

In the search for acceptable substitutes, what are the most important specs to match and which ones are less important. Not all specs are listed in every case either

I imagine I want my voltage, current and gain to be as close to original but how close is "close enough"?

All these numbers are giving me a headache.
 
In order of importance:

1. Form factor...(and along with that, power handling).
2. Vceo - collector-emitter voltage
3. Ic(max) - maximum continuous collector current. Often the circuit only requires a device that can handle a few milliamps, but the device used can take many times that. Knowing this can expand the range of possible subs.
4. Ft - Unity gain frequency
5. Hfe - base to emitter gain

The number of devices available 'now' is pretty diminished even beyond what was available 5 years ago. Through-hole devices are a dead end for most commercial manufacturing, and semiconductor manufacturers are responding my expanding their line of surface mount components while discontinuing the lion's share of through-hole parts. For this reason, transistor substitution will get harder and harder as more and more good devices disappear from the market.
 
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