Are Power Output Transistors from Korean Company No Good for Audio Amplifier?

[Richardjhy]

I have an old Onkyo receiver in which 3 pairs of Toshiba C5198/A1941 used as output transistors for L, R, C channels, and 4 pairs of KEC KTC5242A/KTA1962A used as output transistors for 4 surround channels.

C5198/A1941 are rated 100W, 10A, 140V Vcb, ft=30MHz.
KTC5242A/KTA1962A are rated 130W, 15A, 230V Vcb, ft=30MHz.

Strange application if only consider parameters of output transistors. BTW, all channels have the identical circuitry.

 

[DVDdoug]

It seems a little strange. Are they all on the same circuit board? ...Maybe different boards were made on different days or maybe it was a parts availability issue.

 

[restorer-john]

It'd likely be cost related. The Toshibas are a premium transistor, a very linear device, whereas the KECs are likely much cheaper, less well matched and more applicable to the lower demands of surround channels. The ratings may be reliable or not.

 

[SIY]

The Toshibas are a premium transistor, a very linear device

One hopes not. Circuitry depends on the transfer characteristic to be exponential.

 

[restorer-john]

One hopes not. Circuitry depends on the transfer characteristic to be exponential.

You know what I mean. Cheap Korean power transistors are notoriously poor at high frequencies and high currents in power amplifier stages. They also fail with a monotonous regularity in my experience when called upon to do what a decent Toshiba/Renesas or Sanken with a lower (more conservative) rated device can do in its stride. Likely used here solely due to cost. Do you have another reason in mind?

Ever tried to match a batch of Korean transistors? 50 transistors, 50 bins- no two even close. How to wear out the A-B switch on a curve tracer...

Toshiba delisted and brought back to Japanese ownership:

https://www.reuters.com/markets/deals/toshiba-be-delisted-after-74-years-faces-future-with-new-owners-2023-12-19/

 

[Richardjhy]

It seems a little strange. Are they all on the same circuit board? ...Maybe different boards were made on different days or maybe it was a parts availability issue.

On the same circuit board.

 

[Richardjhy]

You know what I mean. Cheap Korean power transistors are notoriously poor at high frequencies and high currents in power amplifier stages. They also fail with a monotonous regularity in my experience when called upon to do what a decent Toshiba/Renesas or Sanken with a lower (more conservative) rated device can do in its stride. Likely used here solely due to cost. Do you have another reason in mind?

Ever tried to match a batch of Korean transistors? 50 transistors, 50 bins- no two even close. How to wear out the A-B switch on a curve tracer...

Toshiba delisted and brought back to Japanese ownership:

https://www.reuters.com/markets/deals/toshiba-be-delisted-after-74-years-faces-future-with-new-owners-2023-12-19/

So Korean devices are really bad!

 

[Richardjhy]

It'd likely be cost related. The Toshibas are a premium transistor, a very linear device, whereas the KECs are likely much cheaper, less well matched and more applicable to the lower demands of surround channels. The ratings may be reliable or not.

It's an entry level 7.1 receiver, TX-SR503. I think you're right - cost is the only reason.

 

[sam_adams]

Rod Elliott has been investigating fake transistors since 2008. Be smart, buy from a reputable distributor.

 

[SIY]

50 transistors, 50 bins- no two even close.

What characteristic are you binning/matching? Hfe?