Yamaha B-6 Repair attempt and then we'll see...
- Thread starter Asmodeus2112
- Start date
WCGW
Member
The gift that keeps on giving 
So the new transistors “work” channels tracking nicely however the rail switching point is now out of alignment with the transistors and there is a window past 12Vrms where distortion increases and the rail switching lags behind, once it kicks to the 76v rail the distortion is gone again. Not sure what is responsible for the feedback for this system… going to be interesting…
EDIT: Turns out the distortion isn’t symmetrical either, one rail seems to come up before the other…
So the new transistors “work” channels tracking nicely however the rail switching point is now out of alignment with the transistors and there is a window past 12Vrms where distortion increases and the rail switching lags behind, once it kicks to the 76v rail the distortion is gone again. Not sure what is responsible for the feedback for this system… going to be interesting…
EDIT: Turns out the distortion isn’t symmetrical either, one rail seems to come up before the other…
Last edited:
WCGW
Member
Ok so I identified the resistors that needed to be changed that feed into the comparators from the 36V rail along with the channel outputs. I tried a lot of stuff by changing the resistors coupled to the outputs etc with no luck among other things. The transition window happens sooner and faster now and distortion stays in the triple digit range all the way through. Compromise is power consumption and heat rises fast when it switches... I will probably change the rail switching transistors with as good as I can match because the gain matching seems to affect +- voltage rail matching... I changed the resistors from 33k to 47k. Almost got away with 41k but when cold the distortion creeps back in again...
12.3Vrms - 32V collector
13.0Vrms - 33V collector
14.0Vrms - 40V collector
14.6Vrms - 59V collector
15.5Vrms - 73V collector
12.3Vrms - 32V collector
13.0Vrms - 33V collector
14.0Vrms - 40V collector
14.6Vrms - 59V collector
15.5Vrms - 73V collector
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WCGW
Member
So turns out the outputs may not be as direct a replacement as theorised. Encountering rising distortion again past 30Vrms, same as what I resolved with making the rails switch in sooner (not related to my mods though and should have tested this to max power)… This is mirrored on both sides. Only thing I can possibly think of is the base is being driven incorrectly? (B-6 has 4.7ohm resistors on the base).
Now and before pics… Rail is sitting around 72v when distortion starts climbing, increasing the supply rail voltage a little does drop distortion a bit but not huge difference…
Now and before pics… Rail is sitting around 72v when distortion starts climbing, increasing the supply rail voltage a little does drop distortion a bit but not huge difference…
Asmodeus2112
Super Member
Do we know if this is not how B-6's all work? Has anyone tested another B-6 in this way?
WCGW
Member
I have moved on from this project now but I didn’t see it before / someone with different experience claimed it was oscillation starting. I put it as a quirk of the new outputs that wasn’t worth pursuing as it was at very high power levels and it was still inaudible but visible on audio analyser regardless. I covered it all in my final videos including final thermal testing.
Was a fun project and the B-6 honestly wasn’t as bad as I expected overall….
Asmodeus2112
Super Member
After moving interstate and then some unexpected health issues, I am finally back to working on this B-6. Fortunately, it was unharmed during the move and is at the same state that I left it. Powers on, comes out of protection, can adjust bias and dc offset. I added some heat sinks for the outputs so I can start some testing by sending some signals through it. With hope, this might complete the repair portion of this journey and then I can step back and start working on refurb/restoration.
