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Yamaha C-4 | Proper Transistor Replacements

Hi chaps, may somebody know the answer,
I have bought Yamaha C-4, original 2sk100 (y-k100) have been replaced with 2sk170. The former owner sent 2sk100 together with Yamaha. I tested “broken” 2sk100, the result you may see on photo. No chance to know the real story. The owner sent Yamaha for repairing to somebody a couple of years ago.

So , questions are as follows:

  • 2sk100 alive or dead?
  • Master did not have possibility to test 2sk100 and simply replaced with two single transistors for each channel?
  • Is it possible, a test shows good result, but transistor in pcb does not work perfect (exclude bad contact)?IMG_7694.jpegIMG_7695.jpegIMG_7696.jpegIMG_7697.jpeg
 
Hi there AK'ers. So I picked up my second C-4 as a repair job. L channel clipped on the -ve rail side... after some diagnosis with the scope discovered TR617 faulty. I've changed TR605,6 and TR617,18 for TTA/C004's and it works fine and I cant see any response difference on the scope in the 20-20khz range compared to my first C-4 with 2SB649/2SD669's in it. But I'm thinking the reduced Ft of the toshiba's is affecting the mid range-top end sound? It doesn't sound quite as 'crisp'. Long story short, is there an commercially available (digikey/mouser etc.) complimentary pair of replacements for the 2SB649/2SD669's that is suitable for the application?? @avionic any advice?
 
Lp12C4A26 said:
But I'm thinking the reduced Ft of the toshiba's is affecting the mid range-top end sound?
Click to expand...
Ft is usually in the MHz range and has no effect on the audio frequency range (unless it’s really low). Many of these transistors are also targeted toward the HF and VHF applications (transmitters, etc.) and that’s where the Ft number becomes critical. As long as your transistor Ft number is above a few MHz, you should be fine, of course you still need to check other parameters of any replacement transistor for full compatibility.

If you can get the originals, as @Nashou66 suggested, great. If not, TTA and TTC ones should work, however, make sure their hFEs match those of 2SB and 2SD closely, I haven’t checked.
 
avionic said:
What input are you using?
Click to expand...
Aux or Tuner both the same, I use a CXN-V2 streamer for music testing/listening, been living with the selector switch issues for years... in my first unit I've bridged the Phono selector switch in it for MC only. (first one to cause major issues due to the voltage level) Love that MC headamp!! Pairs nicely with my B-2...
 
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