Yamaha B-1 Quickie
- Thread starter rottalpha
- Start date
Yep. dunn. The overload protection circuit works like a charmGood work on your part!You can't rush anything when it comes to this amp and the more you can learn as you go along the better off you'll be when you do your others.
Have you done the 4 ohms to Gnd. test yet? That's a fun one!
and yes, I can think of a rig I will build for my next B-1. I am tired of flipping this thing around...and lucky me, I only have a UC-1 handy for the front panel controls. The silver plate B-1 is 2000+ miles away. I can confidently say I did my workout for the rest of the year already.
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I am having a HOLLY ****! moment for the last half an hour while the B-1 is rocking in the background. 
This B-1 did not get to play Christmas Carols, but it will be rocking the new years eve party
. My trusty MX-1000, which initially gave the unrestored B-1 a well deserved run for its money, will now be demoted from the master of ceremony function.
I have completed the DC balance, Bias then the Idling Current adjustment. I have to admit that it was lot more finicky then I anticipated, even with the 4-turn pots. I could not contain myself and gave it a spin with a set of test speakers and I have not been able to wipe the smile off my face from the first moment I flipped the switch on. I have not completed the THD adjustments yet. I will do that tonight.
Next on the list is to restore the UC-1. Thanks to @avionic for being awesome and for his kind donation of the UC-1 service manual and the 4.7K Arcols. The Arcols already came in really handy for the B-1 adjustment procedures
One observation is that while the B-1 still gets hot, it is nowhere nearly as hot as it was when I ran it the first time (unrestored).
The low-down:
The adjustment procedures for the B-1 are definitely challenging.... The manual is not straight forward at all.
Also, For my next rebuild I will build a permanent jig to adjust and test the next beast.
There are quite a few other lessons learned here such as that many of the original components operate at their spec limits and they would need to be replaced or their original placement be altered.
For example, the cap in the center of the PSU board #2 ABSOLUTELY needs to be moved to the back of the board. I used 105deg, higher voltage than original, long life (5,000hr-27,000hr) caps, all across the PSU boards, but there is no lytic in the world that should be able to take that punishment for a lengthy period of time. This was definitely a design oversight on Yamaha side. Any new cap installed in the original location on PSU board #2 will prematurely fail.
Another mind bending design fail is the power resistors next to the boards. They all need to be raised a few mm away from the boards. In the case of th PSU Board #2 I actually staggered the power resistors so that they do not bake each other to death.
I also replaced all carbon resistors with the cloth sleeve anywhere I found them. The sleeve was an acceptable fire retardant practice but the sleeve also acts as an insulator, essentially trapping the heat inside. These are all carbon resistors with a high PPM, thus already prone to drift. Add the sleeve into the mix and you know they will not stay at rated R when the amp is running. I replaced all carbon resistors on both of the driver boards with 1% 50ppm metal film resistors.
Eventually I will do a retrospective at a more granular level after I am done with the THD adjustments and with restoring the UC-1.
This B-1 did not get to play Christmas Carols, but it will be rocking the new years eve party
. My trusty MX-1000, which initially gave the unrestored B-1 a well deserved run for its money, will now be demoted from the master of ceremony function.I have completed the DC balance, Bias then the Idling Current adjustment. I have to admit that it was lot more finicky then I anticipated, even with the 4-turn pots. I could not contain myself and gave it a spin with a set of test speakers and I have not been able to wipe the smile off my face from the first moment I flipped the switch on. I have not completed the THD adjustments yet. I will do that tonight.
Next on the list is to restore the UC-1. Thanks to @avionic for being awesome and for his kind donation of the UC-1 service manual and the 4.7K Arcols. The Arcols already came in really handy for the B-1 adjustment procedures
One observation is that while the B-1 still gets hot, it is nowhere nearly as hot as it was when I ran it the first time (unrestored).
The low-down:
The adjustment procedures for the B-1 are definitely challenging.... The manual is not straight forward at all.
Also, For my next rebuild I will build a permanent jig to adjust and test the next beast.
There are quite a few other lessons learned here such as that many of the original components operate at their spec limits and they would need to be replaced or their original placement be altered.
For example, the cap in the center of the PSU board #2 ABSOLUTELY needs to be moved to the back of the board. I used 105deg, higher voltage than original, long life (5,000hr-27,000hr) caps, all across the PSU boards, but there is no lytic in the world that should be able to take that punishment for a lengthy period of time. This was definitely a design oversight on Yamaha side. Any new cap installed in the original location on PSU board #2 will prematurely fail.
Another mind bending design fail is the power resistors next to the boards. They all need to be raised a few mm away from the boards. In the case of th PSU Board #2 I actually staggered the power resistors so that they do not bake each other to death.
I also replaced all carbon resistors with the cloth sleeve anywhere I found them. The sleeve was an acceptable fire retardant practice but the sleeve also acts as an insulator, essentially trapping the heat inside. These are all carbon resistors with a high PPM, thus already prone to drift. Add the sleeve into the mix and you know they will not stay at rated R when the amp is running. I replaced all carbon resistors on both of the driver boards with 1% 50ppm metal film resistors.
Eventually I will do a retrospective at a more granular level after I am done with the THD adjustments and with restoring the UC-1.
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B-1 trivia:
after ~ 25 min of minimal use, the heatsinks are at about ~125deg F, while the bank of resistors on PSU board #2 tests at 165-170deg F.
the copper heatsinks I made for the TO-126 replacements on the driver boards are at a steady 125deg F. I am glad I added them. I seen some B-1s where the nasty A810s were replaced with a TO-126 alternative, but with no heatsink. To put things in perspective, the drivers heatsink is at a nice 110deg.
Now I am also wondering if the A810s and their NPN pairs on the driver boards are failing due to heat fatigue, ....hmm
after ~ 25 min of minimal use, the heatsinks are at about ~125deg F, while the bank of resistors on PSU board #2 tests at 165-170deg F.
the copper heatsinks I made for the TO-126 replacements on the driver boards are at a steady 125deg F. I am glad I added them. I seen some B-1s where the nasty A810s were replaced with a TO-126 alternative, but with no heatsink. To put things in perspective, the drivers heatsink is at a nice 110deg.
Now I am also wondering if the A810s and their NPN pairs on the driver boards are failing due to heat fatigue, ....hmm
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Beau Geste
Italia
Nice job . Bravo!
Happy for you (read : envious), great job !
Nice job . Bravo!
Well done Pete
Thank you Gents!
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Mr. Yamaha
Not so much Yamaha lately...
Great work, enjoy it 
yes and no. I hooked up the analyzer to it this morning. At idle, I have 80mV rock steady idling current.
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I am finishing restoring my B-1 and got all the way to the last adjustment in the manual, I'm assuming it is in error.....With idle set at 80mV, when signal is added for a 75w output I get more than double that.....If I adjust for 80mV with signal added, then my idle is 20mV or so....Am I reading it wrong ?
it looks like I am not the only one questioning last step of the adjustment.
With 80mV at idle, the idling current goes to about double that @30dBm
To my thinking what Yamaha is saying in step 3-8 is you're looking to find the optimum combined VR502 and VR504 setting that when found gets you better than 0.06% THD at 30dBm or 75W into 8 ohms at 20kHz and result in a quiescent 80mV at the TP's listed and otherwise know as the 2SK77 sweet spot for those of us lucky enough.
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To my thinking what Yamaha is saying in step 3-8 is you're looking to find the optimum combined VR502 and VR504 setting that when found gets you better than 0.06% THD at 30dBm or 75W into 8 ohms at 20kHz and result in a quiescent 80mV at the TP's listed and otherwise know as the 2SK77 sweet spot for those of us lucky enough.
That is exactly how is spelled, yes. The confusion is the following:
Does it mean that 80mV at 75w with the lowest distortion is the north star we are aiming for and also mean that the idle current will be way lower, yet high enough not to trigger crossover distortion?
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I guess I am hard-headed or I was overthinking this. Either way, I got it now. I will finish off the last adjustment tonight and will report THD results after. Thank you Nick!Pete - Please read my post again ... the 80mV of quiescence is with the 30dBm 20kHz gen. off.
Beau Geste
Italia
Excuse me if I ask a stupid question: the trimmers that you replaced on which values you have set them?
initially, before the adjustment procedures?Excuse me if I ask a stupid question: the trimmers that you replaced on which values you have set them?
Beau Geste
Italia
Yes sir...I think but surely I'm wrong that the best thing was setting the new trimmer with the value of the old ...The old trimmers have the original Yamaha setup. And if everything is OK there should not be any problems, IMHO ...