Pioneer SA-8100 transistor question

The very last thing to do before closing this one up after a major rebuild.

This is about transistors Q3 - Q6 on the power amp board. The original package of these transistors is TO-126 with a b-c-e configuration. There are no TO-126s still available with this configuration which is why all the replacement lists in these forums specify a TO-220 package as replacement. However, the TO-220 don't fit into the original heatsinks.

So, my question is, do we run the TO-220s here without heatsinks or put in new heatsinks (which might be a pretty tight fit)? I have currently got new TO-126s in there with the heatsinks inverted and lifted off the board (pictured) but its only a temporary measure.

WHOA, you're way off the rails here. If what you say is true,
(not a typo, and the heat sinks as well as the board's markings seem to bear you out)
when the list's source parts numbers do NOT MATCH YOUR UNIT, CHECK WITH ME BEFORE ORDERING ANYTHING.

There are most likely other changes that affect the reverse engineering that I did to specify the parts.


Those are the wrong transistor substitutions for the changes on that board. Chances are the subs will be A940 and C2073 transistors, 4mhz versus 150mhz. The board may not be neutralized for RF oscillation with those 150 mhz parts, and if it does oscillate, ---POOF ---- !!!!

you will need to look at every part number from the Service Manual's parts list for the amplifier and post every difference. post pictures of the board, top and bottom - I have to use them to compare to the patterns in the manual.

This work I have to do with/on it will not be quick, days, not hours.

Usually when I specify a to-126, it is replacing a smaller transistor type (like a to-92L) and a heat sink is usually not needed, nor was it provided in the original. Their speeds are usually similar too.

even just the naming of q3 to q6, for the driver transistors, is radically different!!!
also the to-126's I specified are ECB (almost all to-126's ARE), with the leads pointing down, going left to right with the lettering facing you.

just covering all the bases:


NPN (c2690) to-126 installed

Hi Mark

Apologies, I probably should have provided a little more detail.

Firstly, let me first correct a mistake in the opening post. The transistors I'm referring to are Q11 & Q12 (2SD257) and Q13 & Q14 (2SB527). The power amp board on this machine is AWH-022B (full shot of board added, showing some differences, mainly placement of VR3 & VR4).

Secondly, the amp is functioning perfectly in its current configuration -- all voltages on all pins are as per service manual; idle and neutral position are as per manual; DC offset at speaker terminals is about 1.5mv on each channel. Sounds fantastic!

Back to the transistors. As per page 56 of the service manual, these are shown as TO-126 with a B-C-E configuration. I cannot find any TO-126 with a BCE -- they are all, as you say, ECB. This means that in order to use a modern replacement TO-126, the writing on the front of the the transistor must now face towards the back of the amp, hence what you see in my images with the back of the heatsink facing towards us). Replacement transistors in situ are Fairchild BD237 & BD238.

I see in an earlier post that you have recommended the following but the pin arrangement will still mean they would need to be installed as mine have been, with face towards back:


Q11, Q12 2SD357 c or d
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe

Q13, Q14 2SB527 c or d
512-KSA1220AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe


Which brings me back to my original question as to what I might replace these with in order to not have those heat sinks sticking up in the air. Go to a TO-220 or leave them as is?

Thanks.