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Old 5th July 2004, 01:47 PM   #1
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Default any info,manual about Yamaha B-2 ?

pretty nice amp,little bit hard comparing with may aleph. right chanel is dead(transistors) anyone have shematic or know what transistors of V-fet I can use.

originals are yamaha 2sk 76(?) if I am not mistaken..

any sugestions or info welcome..
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Old 6th July 2004, 12:34 AM   #2
anatech is offline anatech  Canada
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Oh wow,
I don't think those transistors are available any more. Totally different case style. Try and find another amp with a dead channel. Also, look up an old Yamaha warranty shop that may have the manual. They may even have a "dead thing" lying around for parts.
Don't forget to check with Yamaha directly.
-Chris
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Old 6th July 2004, 01:04 AM   #3
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Was that the amp that used power JFETs? If so, look
in Google under "unobtainium"

pass:/ gets his unobtainium from Cyclotronguy (no kidding)
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Old 6th July 2004, 03:04 AM   #4
djk is offline djk
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"Totally different case style. "

That was the B1,

"Was that the amp that used power JFETs? "

the B2 used complementary TO3 power JFETS.

Right now on eBay are three different auctions for B2 amplifiers, and some guy selling shop manuals for same.

Real nice chassis, dual mono construction, 57V, big sinks, great meters.

It should be possible to put in BUZ900/905, reverse the gate drives, and re-bias.
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Old 6th July 2004, 04:09 AM   #5
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I wish the power JFETs were available. Too bad the high
end market is too small to support such a device.
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Old 6th July 2004, 04:19 AM   #6
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Quote:
Originally posted by djk
It should be possible to put in BUZ900/905, reverse the gate drives, and re-bias.
Strongly disagree with this. I suppose that anything is possible, but in this case the trouble-to-worth ratio would be astronomical.

The VFETs used in the B-1 and B-2 (different devices for each, as you pointed out) are also known as "static induction transistors" or SITs. These are depletion-mode devices and require about 20 volts of negative bias. This is in contrast to the BUZ enhancement-mode devices that require less than one volt of positive bias.

One of the best sources for information on these amps was an article in Audio Magazine on power FETs by Bascom King in the mid- to late-seventies. It should be available at most university libraries.
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Old 6th July 2004, 04:52 AM   #7
djk is offline djk
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"One of the best sources for information on these amps "

So I guess being an Authorized Yamaha Service Center, having the manuals, spare parts, the card extenders, two days of specialized instruction on these models, being tested on that knowledge, and given the Service Specialist Award doesn't mean anything.

The outputs are no longer available.

Short of gutting it for the chassis, what would you do?
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Old 6th July 2004, 05:28 AM   #8
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Quote:
Originally posted by djk
"One of the best sources for information on these amps "
I should have said "one of the best published sources of information". Besides the service manual, King's article is one of the few things ever published on these amps.

The only other information I have ever seen regarding these types of transistors are some books written by Ed Oxner, formerly with Siliconix. However these specialized publications are quite expensive, over $100 per book.

Quote:
Originally posted by djk
The outputs are no longer available. Short of gutting it for the chassis, what would you do?
You obviously have more hands-on experience than I do with these amps. Still, I would be extremely reluctant to replace the thing (VFETs) that made them unique. Even disregarding the radically different bias requirements, the VFETs are very triode-like, while the MOSFETs are very pentode-like. I would anticipate that such a transformation would significantly change the sonic performance of the amp. Have you successfully performed such a mod?

I suppose I would try a few approaches:

a) Try to find some output devices. I haven't done a thorough search, but some must be available somewhere. If all else fails, one could purchase a complete amplifier on e-Bay for around $250 and use one of the units for spare parts. This would be much easier (and probably cheaper) than trying to re-design the unit to use (radically) different output devices.

b) Sell the amp (or at least the output devices) to someone that needs spare parts and buy/build an amp using easily available parts.

c) Hold your breath and wait until Toshiba puts the silicon-carbide based SITs (SIT = VFET) into production:

http://www.semicon.toshiba.co.jp/rel...sic_presen.pdf
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Old 6th July 2004, 08:32 AM   #9
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Default v-fets

wow, what a great support

I read some articles and now litlle about V-Fets. great devices. but I thougt I can simply use another V-Fet like 2 sk 134/135 and 2sj49/50

or newer (which I can get) 2sk 1530 and 2sj 201. is they not ok?

they cost BIG BUNCH of money in my country..
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Old 6th July 2004, 05:43 PM   #10
rope is offline rope  Bulgaria
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Default Yamaha B2

I have here an old book from 1979 and here is the shematics of this stage.I think you can use the Hitachu mosfets 2Sj49/50/2Sk134/135 pairs or the new equivalents.If you need i can scan the shematics and send it to you.Cheers!
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