Yamaha A-1 Transistor ID

swbeebe

New Member
Hello,
I'm working on a Yamaha A-1 and I need to find out the correct transistor for TR139 or TR140. I couldn't find the part number on the schematic or in the parts list. This amp has had both channels worked on in the past and looks like TR139 and TR140 were both replaced at some point, but may have been replaced by subs. (They are not the same) One may have been replaced with an original, but I can't tell which part number is the correct one. If someone wants to tell me a good current sub that would work, I'd be game for that also. I just like channels to have matching parts. Thanks in advance.
 
That's very odd they left that transistor off of the schematic AND the parts list. Many times you can go to another Yamaha schematic of the same era and the circuits will be very similar, the M-2 uses the 2SC1213 and 2SA914 in it's bias circuit. Do you know what style of transistor it's supposed to be? TO-92 or? What's in there now?

Craig
 
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The PCB layout in the manual also shows 2 TR139 transistors. One is supposed to say TR136. So I'm guessing it's another typo in the manual. The unit currently has a 2N6730 in one channel, and a 2SA673 in the other. I'm sure the 2N6730 is not correct as it has a different orientation and a leg crossed, insulated with heat shrink. The 2SA673 may be the correct part as far as I know, but there has been so many substitutions in the amp, I'm surprised the unit didn't sound different between the channels. If I sub a part, I like to change it in the other channel also so they are both exactly the same. It may not make much of a difference, but it's just a symmetry thing for me.
 
The 2N numbers are American numbers so that is definitely the wrong part, number-wise, electrically it may OK. That transistor is in the bias circuit so it's job along with TR137/138 is to keep a constant DC voltage between the bases of TR525/526 and TR527/528 which are the predrivers. The bias of the predrivers sets the bias of the drivers and then ultimately the output transistors. As long as they are doing that I don't think it will make much difference in the audio signal sound-wise. Do any of those four transistors mount up against the heat-sink? I like symmetry also.
 
TR137 and TR138 are mounted to the heatsink, TR139 and TR140 are not. The TR137, TR138 are listed as 2SC1213 in the manual and don't look like they have been replaced yet. This thing is a mess. The outputs and several other transistors have been differently subbed in both channels, a lot of the flame proof resistors were replaced with carbons, and some series together to make the proper value. (Least I'm guessing they made the proper value, not much left of them..) Has emitter resistors split in two, you name it.
 
When I get stuff like that I usually strip it and start over. The term for Yamaha amps when they go boom is "Chernobyled". The last M-60 I repaired I ended up replacing just over 100 parts. Start making a parts list! I wouldn't hold my breath for original parts though.
 
Decent subs for the 2SA673A/2SC1213A in this case are the KSA708C/KSC1008C (due to the 500mA rating of the A673/C1213). Hfe ranking not a topic here; whatever is available. Do make sure to have the "C" version, otherwise the ECB sequence is different (ranking is indicated by R, O or Y character).

I should also add that the original 2SA673A/2SC1213A had reverse ECB leg orientation compared to other japanese 2SC/2SA transistors: meaning that the orientation (when looking at printed surface) is BCE, as where it normally is ECB.

Problem? Yes and no. When these are stand-alone trannies on the PCB then the sub is just turned 180 degrees. However, when these transistors are pushed over to the heatsink for thermal tracking, then you are screwed when using modern subs (which will have their bulged surface directed towards the heatsink).

It is exactly the case inside the CR-2020, and the only way I could get around it was by using a TO-126 transistor.

Therefore carefully check the ECB points at the PCB by tracing adjacent parts as per schematic. The printing on the PCB might fool you otherwise, blowing all kind of parts in the process during first power up. Actually, this may have happened in your unit as the repair technician was mislead and installed a sub wrongly......pofffff....

As for a butchered amp.... indeed pull everything out and rebuild for 100%. it's what I did with the CR-2020, only using prime parts like all new modern transistors, diodes and Vishay-Dale RN/CMF resistors. The bird sings like an angel.
 
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Yeah, I'm going to go with the assumption that since the M-2 uses a 2SA914 with the 2SC1213, and this one uses a 2SC1213 also, good chance the 2SA914 is the probably the correct part. If I end up subbing parts, least they will be the same in both channels when I'm done. Thanks.
 
2SA917 is nicely a TO-126 style transistor, but 150mA rated. Looking at the schematic, I would say it would do.
Finding a 2SA914 may be hard though.....
A decent modern sub is 2SA1381 (aka KSA1381)
 
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Hello,
I'm working on a Yamaha A-1 and I need to find out the correct transistor for TR139 or TR140. I couldn't find the part number on the schematic or in the parts list. This amp has had both channels worked on in the past and looks like TR139 and TR140 were both replaced at some point, but may have been replaced by subs. (They are not the same) One may have been replaced with an original, but I can't tell which part number is the correct one. If someone wants to tell me a good current sub that would work, I'd be game for that also. I just like channels to have matching parts. Thanks in advance.

Hello
I am sorry but these transistors are on my schematic (see my picture)

TR138 = 2SC1213A and TR140 = 2SA673A

A1.JPG
 
They're not on my schematic or the parts list nor does my schematic have that pictorial of the different semiconductors. Obviously the schematic on HiFi Engine got short changed! Thanx Clinic-Audio!
 
They're not on my schematic or the parts list nor does my schematic have that pictorial of the different semiconductors. Obviously the schematic on HiFi Engine got short changed! Thanx Clinic-Audio!
What do you want for nothing ?:biggrin:
 
If it were my A-1 but it ain't, maybe the OP will pop for it since it looks like he has a mess on his hands.
 
Thanks! I got the schematic from Hi-Fi Engine also. Maybe newer versions of the manual it was corrected. I was just happy for a legible schematic! Thanks again guys.
 
I think I have 5 of these amps now. Rebuilt two of them, one had a bad phono section.



Really a nice amp .

Nashou
 
I only have one that needs to be fixed..
 
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