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Old 30th January 2012, 09:59 PM   #1
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Default YAMAHA B1 AMP 2SK77

HEY I got one of thoses old/rare YAMAHA B1 stereo natural sound amplifiers that I may want to get rid of. Of course the red overprotection light comes on and no sound comes out but the METERS sure are pretty (yes the UC-1 unit). It handled a lot of great gigs at all the big places in Hollywood back in the 70's....sound incredible and VERY QUITE when it comes to noise.
I'm about to take it over to the local YAMAHA wiz and see if he can find the problem or at least tell me if the VFETS ARE good.
Any help out there?
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Old 31st January 2012, 04:14 AM   #2
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Good luck, this is perhaps the most difficult amp to repair.

Art
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Old 31st January 2012, 04:39 AM   #3
anatech is offline anatech  Canada
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Hi downandy,
Be careful here. I was an authorized warranty centre for both Yamaha home and Yamaha MI. Make absolutely sure this fellow was around back then so that he doesn't blow any up in error. Those output devices are unobtainium. The case style is even completely different from anything we have these days.

If the output devices are lost, finding other from dead amps will be both difficult and expensive. A service manual is a must! I wouldn't work on one without the manual in some format, and I've seen them before. Your amplifier is not really repairable any other way - not really. The tech should be able to determine what is blown without removing the outputs. It is possible that a fuse died of old age, or solder joints opened up. Applying power to it without solving all the problems could also blow what were good outputs. In fact, the amplifier must not be plugged in and turned on (yeah, I know you did), don't tempt fate any more than you have already. The proper power up test procedure is to use eyeballs first and look for tell tale signs of trouble. Note that this means that you do not power it up on the bench! If all looks and tests good, power can be applied by bypassing the soft start and increasing the AC line voltage slowly while watching the current meter. Note that an oxidized bias control can also destroy a set of good outputs.

If you need output transistors, the value of the amp is sadly that of a chassis to build another design of amp only. They are expensive to ship, so of low resale value on Eeekbay. Suffice to say that the person who inspects your amplifier needs to know how to work on these and also understand them well. I doubt very much a 40 year old person actually knows how to deal with these. The tech will be an old guy like me. I was a young tech when these things were running around the earth.
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Old 31st January 2012, 06:29 AM   #4
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THANKS AUDIOHEAD AND ANATECH
I know that these are a pain, I started to take it apart and then got smart.....twenty years later! The fuses look good (13?) and I don't see any external device damage. I now have a service manual and a hope and a prayer that the overload protection circuit is at fault but with those gargantuan T03 VFET devices I'll wait to find someone who knows. You got me stuck on the oxidized bias control. And I thought everyone was younger than me! When this amp came out I was just a kid playing Rock and Roll in Hollywood!
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Old 31st January 2012, 08:59 AM   #5
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surprise surprise ...outputs are available in Greece ...strange? ...well not really we have one of the best Yamaha service when it comes to parts ...prize though is astronomical like 48 euro a piece ...but they still have some ....

best regards my friend Chris
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Old 31st January 2012, 09:14 AM   #6
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check out this threads:
Oversized TO-3 TO3 like Yamaha 2SK77 and NEC 2D363 - Overview
2sk77
vfet from hitachi 2SK77,2SK76,2SJ26???
Successors for V-FET SONY-Yamaha-TOKIN 2SJ28, 2SJ18/2SK60, 2SJ26/2SK76 and 2SK180
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Old 31st January 2012, 09:17 AM   #7
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Quote:
Originally Posted by sakis View Post
surprise surprise ...outputs are available in Greece ...strange? ...well not really we have one of the best Yamaha service when it comes to parts ...prize though is astronomical like 48 euro a piece ...but they still have some.
A link to a shop would be nice, thx.
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Old 31st January 2012, 10:42 AM   #8
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Quote:
Originally Posted by sakis View Post
surprise surprise ...outputs are available in Greece ...strange? ...well not really we have one of the best Yamaha service when it comes to parts ...prize though is astronomical like 48 euro a piece ...but they still have some ....

best regards my friend Chris
I guess, the price of 48 euros/pc is very very cheap for a 2SK77 in new condition. Please let me know the provider/supplier.
Keep in mind - the user does not have the intention to obtain an inexpensive amplifier for cost effectice repair. Rather the desire, to get the original/genuine condition after repair service is the most important thing.

here additional links:
http://my.coolala.net/upload0713/201...1286557087.gif
?????????????: ??????????????
I??????????? - ??????Blog?
???????? - ????Miyuki.Taira?????

Last edited by tiefbassuebertr; 31st January 2012 at 10:50 AM.
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Old 5th February 2012, 08:56 AM   #9
djk is offline djk
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Yamaha has some board extenders for this amplifier, they used to let you use them for postage costs (with a $200 deposit).
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Old 25th February 2012, 12:43 PM   #10
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Default 2SK77

PLEASE TELL ME MORE ABOUT THESE PARTS FOR THE YAMAHA B1, and anything on the board extenders.
Thank You
Andy

Quote:
Originally Posted by tiefbassuebertr View Post
I guess, the price of 48 euros/pc is very very cheap for a 2SK77 in new condition. Please let me know the provider/supplier.
Keep in mind - the user does not have the intention to obtain an inexpensive amplifier for cost effectice repair. Rather the desire, to get the original/genuine condition after repair service is the most important thing.

here additional links:
http://my.coolala.net/upload0713/201...1286557087.gif
?????????????: ??????????????
I??????????? - ??????Blog?
???????? - ????Miyuki.Taira?????
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