Pioneer SA-708 transistor replacements

[Meesterstech]

I am working on a Pioneer SA-708 and would like to know if I can replace the 2SC2238/2SA968 transistors with ON Semi's MJE15032G/MJE15033G? The manual also states that these 4 transistors should be hfe matched. (unless that was someone else s notes)<br />
<br />
I found that the left channel has had most of its transistors replaced with RCA SK series, as well as the 4 output transistors on the heatsink.<br />
<br />
The Left Channel had 0mV bias reading.<br />
The Right Channel had 150+ mV bias reading.<br />
<br />
Also the 2SA949 which sets the bias for the outputs was changed on the Left Channel (the channel with a zero bias reading)<br />
<br />
Here is a list of transistors I have in stock, hoping most of these will work:<br />
MJE15032G/MJE15033G<br />
KSC1845FTA<br />
KSA992FBU<br />
KSA1013YBU<br />
KSC2383YTA<br />
KSA1220AYS<br />
KSC2690AYS<br />
<br />
Here are all the transistors I want to change:<br />
2SA726S<br />
2SC2229<br />
2SA949<br />
2SA968<br />
2SC2238<br />
<br />
I know I'm getting off topic here. Biggest concern is whether I can replace 2SC2238/2SA968 transistors with ON Semi's MJE15032G/MJE15033G.<br/>

 

[markthefixer]

You really made me work for this one, sorting out the mashup... Finally started from scratch:

q401 2sa798 dual, so use a pair of ksa992, close thermal contact would be nice...
q403 2sc2291 dual so use a pair of ksc1845, close thermal contact would be nice...
q405 2sa726 ksa992

q407 2sc2229 to-92L npn 150v 50mA 0.8w 70-240hfe 120mhz position dissipates 0.214 watt approx
q409 2sa949 to-92L npn 150v 50mA 0.8w 70-240hfe 120mhz position dissipates 0.214 watt approx

q411 2sa968 to-220 pnp 200v 1.5a 25w 70-240hfe 100mhz
q413 2sc2238 to-220 npn 200v 1.5a 25w 70-240hfe 100mhz
These driver transistors have been neutralized by 220pF caps base to collector. Thus the actual response of the circuit is slower than 100 mhz.


------------------ q401, q403, q405 ------------------------
512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 300-600hfe $0.17 ea
512-KSC1845FTA (ln)to-92 ecb 120v .05a .5w 100mhz 300-600hfe $0.05 ea

------------------ q407, q409, -----------------------------

512-KSA1013YBU to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.34 (R=60-120, O=100/200, Y=160/320)
512-KSC2383YTA to-92L ecb 160v 1a .9w 50mhz 160-320hfe $0.17
or
512-KSA1220AYS to-126 ecb 120/a160 1.2a 1.2w/20w 175mhz 35-320hfe $0.39 (R=60-120, O=100/200, Y=160/320)
512-KSC2690AYS to-126 ecb 120/a160 1.2a 1.2w/20w 175mhz 35-320hfe $0.40
if the leads can fit the holes, the to-126's will run cooler.
THAT'S why they went with the to-92L's originally,to shed heat.

------------------ q411, q413, -----------------------------
some other on-semi choices:
863-MJE15029G pnp to-220 bce 120v 8a 50w 30mhz 70hfe $1.30 watch the Vbe turnon!!
863-MJE15028G npn to-220 bce 120v 8a 50w 30mhz 70hfe $1.30

863-MJE15031G pnp to-220 bce 150v 8a 50w 30mhz 70hfe $1.30 watch the Vbe turnon!!
863-MJE15030G npn to-220 bce 150v 8a 50w 30mhz 70hfe $1.30

863-MJE15033G pnp to-220 bce 250v 8a 50w 30mhz 70hfe $1.30 watch the Vbe turnon!!
863-MJE15032G npn to-220 bce 250v 8a 50w 30mhz 70hfe $1.30

863-MJE15035G pnp to-220 bce 350v 4a 50w 30mhz 100hfe $1.25
863-MJE15034G npn to-220 bce 350v 4a 50w 30mhz 100hfe $1.07

BUT THERE IS A CATCH!!!! The On-Semi's have a slightly lower Vbe loss, which can upset the thermal bias diode / transistor voltage drop assumptions in the design, resulting in an unintended HIGHER idle current that MAY not be able to be adjusted low enough to make spec.

thus:
757-2SA1837(F,M) pnp to-220 bce 230v 1a 20w 70mhz 100-320hfe 70mhz nsa driver
757-2SC4793(F,M) npn to-220 bce 230v 1a 20w 100mhz 100-320hfe 100mhz nsa driver
or (** preferred, due to the extra amp of drive **)
757-2SA1930(Q,M) pnp to-220 bce 180v 2a 20w 200mhz 50-320hfe 200mhz nsa driver
757-2SC5171(Q,M) npn to-220 bce 180v 2a 20w 200mhz 50-320hfe 200mhz nsa driver

 

[Meesterstech]

I was not expecting anyone to go to this much work. You are the man and I OWE you!!

I really do appreciate it, that was a crap load of work.

 

[Meesterstech]

Looks like I will be using A1837/C4793's. I will have to make an order, I don't have any of these on hand.

 

[markthefixer]

Sorry about the On-Semi's, but finding out afterward that the idle current is too high and can't be dialed down, sux....

I LOVE them for power supplies....


uh, 4793's are back ordered at mouser iirc... and the 5171's are just a few cents more... and I think the 220 pF caps are enough to "tame" them.

 

[Meesterstech]

How about the outputs, they were swapped with RCA. Would ON Semi's be better quality?

 

[markthefixer]

you are working on a sa-708 and a sa-7800??? why two threads?

ahhh, I see - thread hijack....

 

[Meesterstech]

I'm sorry I didn't mean to hijack this thread, got ahead of myself.

Sorry about that!

 

[Meesterstech]

Hey Mark, the two large filter caps have an exclamation mark in the manual. Is this for the capacitance only, or for the voltage as well?

 

[markthefixer]

Hey Mark, the two large filter caps have an exclamation mark in the manual. Is this for the capacitance only, or for the voltage as well?

you are going to drive me nuts.

You are working on an sa-708 (which is a conventional amp) in this thread

AND

in groenhen's sa-7800 thread (an NSA amp) you are talking about
"outputs (2SA1075 & 2SC2525) were replaced with RCA's."....
implying a sa-7800

Both have similar outward appearance until you look closely.

Then throw in MrAndyPants's sa-7800 with (former) main cap problems

and I get a severe case of mental whiplash.

WHAT's the deal?

In the sa-708

1200uf 56v for the main caps in a sa-708
It runs +/- 46v on them.

UPW cap choices for 1200uf are 50v and 63v
caps were originally -20%, +80% capacitance spec and 15% voltage spec, so going higher in capacitance wouldn't hurt, and the limiting factor is the inrush current's effects on the power rectifier diodes (sr3am-4), so you could put in 1n5404's and safely go higher in capacitance as long as they physically fit in the space. Voltage is always OK to increase (within reason)
Caps nowadays typically are 10% in voltage spec.
so 46 to 50(55) is iffy coming directly off a power line (spikes?), 63 is a better choice, given that the next Nichicon step up here is to 100v and that entails a significant increase in physical size.

 

[FranksElect]

good morning , Mark , iive got a sa-708 on the bench having to replace the outputs 2sa1075 and 2sc2525 , the ones Ive ordered on ebay china finaly got here , but they are a bit bigger than the originals , will not fit in the pc hole unless modified . Do you have a better replacement number that fits correctly ? thanks