What are suitable replacements for power transistors SK A769 and SK C1827?

Semiconductor Discrete Semiconductor Products
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1

Looking for suitable replacement power transistors for vintage Sansui A 40 amplifier.
SK A 769 and SK C1827.
Thanks.

2

Hello @cjdean,

That is a very nice little amplifier. The transistors in question are a complimentary pair used in the power amplifier section.

You may find the NPN BD243CG and the PNP BD244CG to be reasonable replacements for this application:

  1. Please verify the device pin out is the same. If I have done my work correctly this is a BCE configuration (front view left to right).

  2. Verify parameters such as V_{CE} max, I_C max, and DC gain.

  3. Understand that the amplifier may have been tightly designed for the unique characteristic of the A769 and C1827. It’s possible, but unlikely, that the amplifier will be unstable with the replacement transistors.

Tech Tip: Most transistor audio amplifiers feature direct coupled stages. A defective output transistor can cause damage to the driver transistors or even the primary voltage amplification stage. While I would not recommend replacing all of the transistors en masse, you may want to purchase replacements just in case. Also, you may want to purchase a few spare BD24XCG pairs as they may be good for future projects.

Best wishes,

APDahlen

P.S. If you have not already done so, you may want to visit this page for a service manual and schematic.

P.P.S. Don’t forget the mica insulators and heatsink compound.

3

Hi there, thanks for that, they check out as suitable replacements and have ordered 5 of each to get a good match. Small Sansui, but good looking, when it’s tidied up it will do the job just fine.
Have found transistors difficult to match these obsolete types.
How about these…
KSC2690 in place of 2SD357 ? The KSC2690 has slightly higher v and more amps, 1.2amp. Larger but close, is it okay?
Also looking for replacement for 2SB 527 ? No luck yet.
Thanks Chas Dean.

4

Hello Chris,

There are a few tricks I use when searching for replacements semiconductors.

  1. Use NTE electronics where possible and then link the parts back into DigiKey. NTE has a long history of providing replacement semiconductors. The is very convenient for service personnel as a small number of semiconductor components may be used as substitutions.
    This is perhaps easiest way to locate substitutions as the hard work has already been done. In this case, you could use the NTE373 and NTE374 pair. Unfortunately, they are not currently listed in DigiKey Marketplace. Please see the video link below for information on the technique.

  2. Direct substitution using parameters. This is harder as we need to pay attention to critical parameters. Occasionally I will use a substitution for the substitution by using the NTE data such as this NTE373 and NTE374 complimentary pair.

It looks like you have the hang of these techniques as your KSC2690 in place of 2SD357 is a reasonable substitution. You should have no problems locating a replacement for the 2SB527.

Best wishes,

APDahlen