So that is how a rebuilt B-1 sounds, I am having a HOLLY SHIT! 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 was definitely challenging...at least for me it was. Partially my fault for not picking a better time of the year (not during the holidays) for the rebuild because some of the B-1 seasoned techs here, did not have the time to help as they usually do. The manual is not straight forward at all.
Most important lesson learned: 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.
Because there is substantial heat generated within this unit, there is no reason to keep any of the original ceramic caps. True, some have functions that are not capacitance value critical, but I doubt that a wide tolerance is acceptable for all functions.I used silver mica for the small pf caps and polypropylene for the nf values. I did not have replacements for all, but I will be going back in there at some point in the future.
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 eachother 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.