YAMAHA b1 amplifier repair
Hello
I do repair YAMAHA B1 without any problem . It takes a long long time because specific process is necessary .
I do confirm that factory service manual has many error and you have to know what you do if you don't want to dammage precious V-FET transistors !
Don't hesitate to send me PM if you need help !
Hello
I do repair YAMAHA B1 without any problem . It takes a long long time because specific process is necessary .
I do confirm that factory service manual has many error and you have to know what you do if you don't want to dammage precious V-FET transistors !
Don't hesitate to send me PM if you need help !
The Japanese use 2SK180C or 2SK180D to repair B1s, which are still obtainable if you look hard enough.
I can swap a matched quad of 2SK180C or 2SK180D with your 4 pieces of 2SK77 from the B1 (assuming 2 of them are dead, and 2 remains working), but then you need to find someone who have the skills to fix it with the 2SK180s. PM me if interested.
This is an example of such a repair (Google translate will be handy):
However, given the weight of the unit, shipping overseas will be way too expensive, so you really have to source a repair shop in your own country.
Good luck.
Hi Tim, what is your experience with C rank SK180s?
are they closer to the SK77s than the D rank?
Let me try to be polite here and mention that certain people should look up what a Yamaha B1 is before offering any advice. Burn marks on output devices? They are 20A VFETs in a giant TO3 metal case! Even most experienced techs will diagnose them shorted because VFETs are a depletion device, so completely on at rest with no bias. Fortunately, they come in plug-in heat-sink modules and if you know how to test them with a DMM, it's easy to do.
The B1 is perhaps the one no-compromise showcase amplifier Yamaha ever did, retailing for a price of two good cars back in 1975 when it first appeared. Topologically you can pretty much say it is unique among solid state amplifiers, partly because it exclusively uses VFETs (SITs) and JFETs for everything except 'housekeeping' tasks like providing constant current and voltage regulation. Yamaha developed all the semiconductors that handle the amplification part specially fort his amplifier and they are not used in any other amplifier anyone including Yamaha ever made. They are pretty much irreplaceable except by salvaging from a parts unit.
To make things even worse, the service manual has a few subtle but potentially disastrous errors for someone who does not understand how this amp works (on the other hand, the circuit description section is very good).
That being said:
A SINGLE genuine and working 2SK77 will set you back upwards of 50$ and often twice that (that is, IF you know where to look), there are 4 in there. 2SK75 is practically unobtainable, and there are a number of them in that amp, never mind the other special JFETs. Although I would consider pulling it apart an atrocity, it's worth the asking price in parts, especially for someone who already has a working unit. The UC1 controller recently went on eBay for well over that price, and this has classical components in it.
Finally, THAT being said, if you understand the (ample) amount of circuitry, the B1 is not that easy to kill, because there are several levels of protection. The problem, is that if the error persists and the user continues to, say, replace burnt fuses by ever higher ratings, the protection circuits will fail, and the unobtainium VFETs will fry.
The amp itself is a tour-de-force, it is built like a tank and in fact you will be hard pressed to find anything comparable to it. I am talking two layer epoxy gold plated boards from 1975, so more like a high quality measuring instrument rather than a power amp.
If I was not in Europe, I'd be jumping on that $300 offer immediately. But then, I know what it is and already own one
I went throught the adjustments procedures for one of these fantastic machines recently and it felt like Yamaha USA used some sort of 1970s version of Google translate to put toghether the english version of the B-1 service manual.
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The 2DK180 C-rank has a higher Vp (more negative) than the D-rank, otherwise they’re the same. The 2SK77 Vp has a range also, so it’s hard to say which rank is closer to 2SK77, you’ll need to adjust the bias to adapt.
Thank you!
in terms of matching pairs: do they need to be further matched when they are already of the same rank?
I've restored 6 of these and I would say from experience no further matching is required within Yamaha's 2SK77 ranking codes.
By now I've restored 6 of these and if we’re talking about repairing B1, I would say further no matching is required.
sorry I missed your response.
You mean you fixed 6 B-1s with Tokin 2sk180 C or D rank?
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