Pioneer SA-500 transistor questions

[F1nut]

I have a Pioneer SA-500 integrated amp that I forgot I had, so I decided to bring it back to life. I have replaced all the caps and the 4 emitter resistors (one looked like it was falling apart), which went well. I then found one of the 2SC458LG's was noisy, so I replaced both with 2SC2240's (marked C2240/GR 5J), which seemed to be the recommended replacement. I have now discovered that one of the 2SC870's is noisy, so I would like to replace all the 2SC870's and 871's. This is the part I'm having trouble with. I have seen recommendations for the 2N3707 and the KSC1845, but the specs are very different. I understand caps and resistors, but this transistor stuff has my head spinning.

I'm hoping someone can point me in the right direction and perhaps enlighten me a bit on what specs are the important ones when attempting to sub transistors.

 

[markthefixer]

Found this from a year ago:

Could I please get verification on transistor selections listed below?
The selections were copied from previous threads.

HEAD AMP W15-032
q1,q2 - 2sc871 >>>KSC1845FTA
q3,q4 - 2sc870 >>>KSC1845FTA

CONTROL AMP W15-033
q1,q2 - 2sc870 >>>KSC1845FTA

MAIN AMP W15-055
q1,q2 - 2sc458LG >>>KSC1845FTA
q3,q4,q5,q6 - 2sc734 >>>KSC945GTA
q7,q8 - 2sa561 >>>KSA1015GRTA

MAIN AMP W15-055
q1,q2 - 2sc458LG >>>KSC1845FTA
q3,q4 - 2sc734 >>>KSC1845FTA

q5,q6 - 2sc734 >>> 512-KSC2383YTA
q7,q8 - 2sa561 >>>512-KSA1013YBU

512-KSA1013YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe
512-KSC2383YTA to-92L ecb 160v 1a .9w 50mhz 160-320hfe

______________________________________

I always have a little trouble with selecting Trim Pots, if I could please get help on these.
vr1,vr2 - 30KΩ(B) Semi Fixed
vr3,vr4 - 100Ω(B) Semi Fixed

the trim pots depend upon what direction the adjustments are to be made from.

652-3386H-1-101LF 100 ohm single turn
your choice:
652-3386H-1-503LF 50k ohm single turn
652-3296P-1-503LF 50k ohm multi-turn

better post pix of the old in the chassis to be sure they fit.

 

[F1nut]

Mark, thanks for your response. Your quoted post was one I found in my search for answers. I'm having trouble understanding how the KSC1845FTA can be the sub for the many different transistors, all with different specs.

Is the voltage the same as with caps, as long as it is equal to or greater than the original all is good?

What about the current gain bandwidth? For example, the 2SC870 is rated at 150MHz while the KSC1845FTA is 110MHz.

 

[markthefixer]

The values of other parts swamp out those effects.

There are trade offs, Hfe changes with collector current etc...
They were still learning how to make transistors. Lots of parts numbers, lots of trade offs. Specs are limits: voltage, current, power dissipation, gain (collector current versus base current needed), speed. If a replacement transistor is capable of better than the circuit needs, no problem.

110 vs 150 mhz... Are we taking audio amps, or FM / TV tuners?
BTW a tuner transistor can be 300 mhz...

And I am not going to debate this. It's called engineering. I'm not even going to try to start teaching that.

For example, 2sc2240 - looking it up yields the appellation "obsolete"
Checking with the Fairchild site, the cross for the 2sc2240 is ksc1845...

I'm just happy that the ksc1845 and ksa992 have remained currently supplied over all these years. Keeping the lists here doable.
The demand for low noise higher voltage amplifier type transistors in individual packages has to be declining.

These are lower frequency amps, If you look at Pioneer's NSA amps, they need 30 to 60 mhz outputs, and 200mhz drivers to achieve the low distortion they were designed for.

 

[F1nut]

Ok, well thanks for the help.