Thanks in advance for reading 
What started as a faint hum in the left site of my 2CH Marantz amp has inspired me to rebuild the whole thing on perf board.
(The gold/black theme was completely by accident. Had no idea the protoboard had gold contacts on top.)
Sadly a 2SC3423 transistor has transitioned into the afterlife, and I think the upstream 2SC2705 has terminal cancer (hFE is 74). I do not wish to spend $40 getting two exact replacements to Canada and find out that they're fakes.
(enlarge)
One question I have is whether Q721 sees more than 40V? The A1015/C1815 would be a good candidate but Vce-max is only 50V.
I have on hand:
New from Digikey:
10x sets: BC557B/BC447B https://www.onsemi.com/pdf/datasheet/bc556bta-d.pdf
2x sets: KSA1381E/2SC3503D https://www.onsemi.com/pdf/datasheet/ksa1381-d.pdf https://www.onsemi.com/pdf/datasheet/ksc3503-d.pdf
4x sets: KSA1015Y/KSC1815Y https://www.onsemi.cn/PowerSolutions/document/KSA1015-D.pdf https://rocelec.widen.net/view/pdf/riwfxedwmh/ONSM-S-A0003585266-1.pdf
Also authentic Sony pulls: 1x set 2SC3421Y (hFE 153)/2SA1358 and 5x sets 2SC1815 (hFE 241)/988a
Can you please recommend replacements for Q721 and Q725 based on what I have?
A) Replace left-side C2705 (Q721) in section E with right-side C3423 from section F (hFE 188). Replace all of section F with A1381/C3503 sets?
B) Use BC557B/BC447B (voltage?) for both sections E and F (because noise doesn't matter in the driver stage?)?
C) Replace all of section E with KSA1015Y/KSC1815Y (voltage?) sets and all of section F with KSA1381E/2SC3503D?
D) Replace all of section E with section F plus the one C3421Y, and all of section F with A1381/C3503 sets
E) Other?
What started as a faint hum in the left site of my 2CH Marantz amp has inspired me to rebuild the whole thing on perf board.
(The gold/black theme was completely by accident. Had no idea the protoboard had gold contacts on top.)
Sadly a 2SC3423 transistor has transitioned into the afterlife, and I think the upstream 2SC2705 has terminal cancer (hFE is 74). I do not wish to spend $40 getting two exact replacements to Canada and find out that they're fakes.
One question I have is whether Q721 sees more than 40V? The A1015/C1815 would be a good candidate but Vce-max is only 50V.
I have on hand:
New from Digikey:
10x sets: BC557B/BC447B https://www.onsemi.com/pdf/datasheet/bc556bta-d.pdf
2x sets: KSA1381E/2SC3503D https://www.onsemi.com/pdf/datasheet/ksa1381-d.pdf https://www.onsemi.com/pdf/datasheet/ksc3503-d.pdf
4x sets: KSA1015Y/KSC1815Y https://www.onsemi.cn/PowerSolutions/document/KSA1015-D.pdf https://rocelec.widen.net/view/pdf/riwfxedwmh/ONSM-S-A0003585266-1.pdf
Also authentic Sony pulls: 1x set 2SC3421Y (hFE 153)/2SA1358 and 5x sets 2SC1815 (hFE 241)/988a
Can you please recommend replacements for Q721 and Q725 based on what I have?
A) Replace left-side C2705 (Q721) in section E with right-side C3423 from section F (hFE 188). Replace all of section F with A1381/C3503 sets?
B) Use BC557B/BC447B (voltage?) for both sections E and F (because noise doesn't matter in the driver stage?)?
C) Replace all of section E with KSA1015Y/KSC1815Y (voltage?) sets and all of section F with KSA1381E/2SC3503D?
D) Replace all of section E with section F plus the one C3421Y, and all of section F with A1381/C3503 sets
E) Other?
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Hi kwadrofonik
Not sure that I can answer all your questions, but
Q721 and Q723 both see the full output swing - I would not use anything with a Vce-max less than 100V (and that would be cutting it close)
No: too low Vce-max
Vce-max: OK and comparable Ft
No: too low Vce-max
2SC3421Y is likely OK for Q725
2SC1815: too low Vce-max
I know it is not answers to all your questions, but I am running out of time
BTW: googling after "datasheet <component>" is a rather efficient help in making the basic evaluation whether a component can replace another
Cheers,
Martin
Not sure that I can answer all your questions, but
Q721 and Q723 both see the full output swing - I would not use anything with a Vce-max less than 100V (and that would be cutting it close)
No: too low Vce-max
Vce-max: OK and comparable Ft
No: too low Vce-max
2SC3421Y is likely OK for Q725
2SC1815: too low Vce-max
I know it is not answers to all your questions, but I am running out of time
BTW: googling after "datasheet <component>" is a rather efficient help in making the basic evaluation whether a component can replace another
Cheers,
Martin
The q721 725 have no collector resistors. just emitter resistors, 47 to the drivers and the drivers have 10 ohm emitter resistors.
If I guess right from the picture that 721 725 are TO92 transistors, this is a recipe for disaster. I they are TO 126 then that is sort of okay, but not if they blew up.
On stuff I get from newark & digikey is real. Don't buy from newark in canada, UPS loan fee. I'd use MJE15028/29 for 721/725 although some of the purists here would use BD139/140 for low capacitance. I'd add heat sinks to them, too. Lots of drivers & predrivers blown up in consumer amps with no heat sinks to save $1 each human handling. You're human handling is free, and you're not trying to sell your amp for $10 less than every body else at that wattage rating.
I wouldn't sweat the noise specs. If you've seen pictures of fab with all automation handlers & no humans but maintenance in tyvek suits, there is no more hair or skin flakes floating around the fab room. The On stuff I've got has been very quiet & high gain without noise specs. Only reason I'd buy a BC anything in TO92 is to get bce or ecb if the pcb required it. For TO92 I use MPSA06/56 ebc for rails up to 65 volts. Yours is 40. Else MPS8099/8599 if I can get them, they were once a lot cheaper for some reason. The last I measured the gain on some @ about 300, so I wouldn't worry much these days about having enough gain from On parts.
If I guess right from the picture that 721 725 are TO92 transistors, this is a recipe for disaster. I they are TO 126 then that is sort of okay, but not if they blew up.
On stuff I get from newark & digikey is real. Don't buy from newark in canada, UPS loan fee. I'd use MJE15028/29 for 721/725 although some of the purists here would use BD139/140 for low capacitance. I'd add heat sinks to them, too. Lots of drivers & predrivers blown up in consumer amps with no heat sinks to save $1 each human handling. You're human handling is free, and you're not trying to sell your amp for $10 less than every body else at that wattage rating.
I wouldn't sweat the noise specs. If you've seen pictures of fab with all automation handlers & no humans but maintenance in tyvek suits, there is no more hair or skin flakes floating around the fab room. The On stuff I've got has been very quiet & high gain without noise specs. Only reason I'd buy a BC anything in TO92 is to get bce or ecb if the pcb required it. For TO92 I use MPSA06/56 ebc for rails up to 65 volts. Yours is 40. Else MPS8099/8599 if I can get them, they were once a lot cheaper for some reason. The last I measured the gain on some @ about 300, so I wouldn't worry much these days about having enough gain from On parts.
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Thank you both! I guess that rules out the A1015/1815Y unless I swapped them with a 970/2240 combo on the input stage and I don't think they can really handle power.
I probably spent hours googling "datasheet <component>" to find a suitable replacement that I can buy from Mouser or Digikey because those are the only sources I trust (I should be looking at Newark USA too I guess). I wish I had picked up on Q721's sickness sooner or I would have ordered two more pairs of KSA1381E/2SC3503D.
And yes I agree indianajo. BC-anything is the last option I'd want in my amp. That's why I still have 10 sets.
So based on your advice I'm leaning toward option D.
I probably spent hours googling "datasheet <component>" to find a suitable replacement that I can buy from Mouser or Digikey because those are the only sources I trust (I should be looking at Newark USA too I guess). I wish I had picked up on Q721's sickness sooner or I would have ordered two more pairs of KSA1381E/2SC3503D.
And yes I agree indianajo. BC-anything is the last option I'd want in my amp. That's why I still have 10 sets.
So based on your advice I'm leaning toward option D.