Yamaha B2 hum

BrandXRC

BrandXRC
I have had this B2 along with the C2 preamp for a year or so. Great sounding amp.:music: I got them at a garage sale cheap. The preamp and speaker switches on the amp needed cleaning bad. All was working well, except one or the other channel would drop out at times, and a flick of the preamp 1-2 switch always cleared it up. I got in the habit of flicking the switch a couple of times before turning on the amp, or at least before turning up the volume. I did this the other day and with the amp on and the volume down, and simultaneous with one flick of the switch, a hum appeared. I thought maybe the switch had "died" so I bypassed the switch with preamp 1 and unhooked preamp 2 input, the hum is still there. Both channels even. If you turn up volume past about 8 oclock, the music will overcome the hum. Anyone familiar with this amp, and have any ideas what I screwed up. :sigh:
 
Disconnect the preamp. Still hums? The B2 may need new caps. This is a vital thing on a VFET amp, as its life depends on the reliability of the +/-85V regulated supply. If either of these supplies goes away, the VFET's self-destruct and you have a paperweight.

It is also possible that the four large power supply caps need replacement, but if the hum is indeed coming from the amp, then the small electrolytics on the regulator board are the suspect ones. But, Michael Percy Audio sells a nice Nichicon 22,000µf 63V cap that can be squeezed into place (barely, and requires relocating some wiring) if the large caps really need replacing.

The regulator and the meter driver circuitry are also full of the dreaded 2SC458 transistors which should be considered bad right off the bat (failure rate approaching 100%). I generally replace these with Panasonic 2SC1509S from Digikey.
 
Thanks alot Echo. Yes hums with no preamp. I see the 458's. All of them have nasty looking black legs. What Im thinking is a recap of that board. And the 458's. If I'm not mistaken, there is not really alot of other parts common to both sides of the amp. Or am I wrong? Is there anything else on that board that sould be taken care of at the same time?
Picture051.jpg
 
New zener diodes, perhaps. D205 & D206 are 30V 1W zeners, and D210 is a 1/2W 13V zener. TR207 and TR208 get pretty toasty, and can be replaced for reliability with On-Semi MJE15032 and MJE15033.

Put new speaker relays in there while you're at it. They should be Omron LY-style, 12V, PC-mount. Digikey #Z978-ND. And I'd replace the relay driver transistor (TR216). You can use the Zetex ZTX694B, but be aware that the pinout is different than the original transistor and will require some creative lead bending (or you can use another Panasonic 2SC1509S here and uncomplicate things a little).

Always download the data sheets for a new transistor to make sure you're familiar with the lead arrangement.
 
Thanks again. I will get up a parts order. Should I get different caps for the black, and the blue caps? and Do you know of a replacement for the preamp input switch?
 
The B2 sings again :banana:
Thank you Echowars, I recapped the regulator board, Changed a few 458"s.
I sure appreciate you taking the time to lead me in the right direction...
You are the man...
 
New zener diodes, perhaps. D205 & D206 are 30V 1W zeners, and D210 is a 1/2W 13V zener. TR207 and TR208 get pretty toasty, and can be replaced for reliability with On-Semi MJE15032 and MJE15033.

Put new speaker relays in there while you're at it. They should be Omron LY-style, 12V, PC-mount. Digikey #Z978-ND. And I'd replace the relay driver transistor (TR216). You can use the Zetex ZTX694B, but be aware that the pinout is different than the original transistor and will require some creative lead bending (or you can use another Panasonic 2SC1509S here and uncomplicate things a little).

Always download the data sheets for a new transistor to make sure you're familiar with the lead arrangement.
Hello EW. Are those Panasonic trannies listed on page 1250 of the digi-key
catalog and listed as 2sc15090S-ND? Also if I cannot find the Panasonics
that you gave will the Zetex 694B work as well instead of the dread 458's.
I say this because of you saying that you could use the Panasonic on TR216.:scratch2:
Thanks,
Klipschhornman

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Yamaha B-1's and B-2's, C-1,C-2 T-80,PX-3
 
Why we don't have a dedicated Yamaha section in the Manufacturer Forum? I think it would be convenient to discuss Yamaha there.
 
Well, repairs are repairs~
Would be nice to let the techs loose with their own forum. Might want to ask the techs first.:scratch2:
 
Why we don't have a dedicated Yamaha section in the Manufacturer Forum? I think it would be convenient to discuss Yamaha there.

The more separated it becomes, the more I think it degrades the site personally. Not that anyone cares about my opinion.

I have never read any of the 9K post in sansui, or the 9K in Pioneer, or the 4K in the Marantz forum. And the search function is lack luster at best.

Opinion is now turned off.
 
That's them.
Hello EW, went to the site and typed it in exactly and it
says invalid part no. :sigh: Also, when ordering resistors, should I
get the flame proof type or just carbon film, but better stuff than
really cheap ones. I'm not naming names of cheap ones, saw where
one discussion went. Do you know where I can find good trannies for
the Sony V-fet amps. I'm not talking about the outputs. Just power board,
power supply. Ceitron has a look up data base, but also says it sells
parts from(The part company that must not be named):nono: and I don't want them. As you say, maybe only as a last resort. I'm not asking you to
do the legwork, heavens knows that you're busy enough, just point me in
the right direction and push me down the hill. Thanks,
Klipschornman

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It riles them to believe that you perceive the web they weave
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Yamaha B-1's, B-2's, PX-3's, C-1, C-2, T-80
Klipschorns, ESS, Advent, EPI JBL L100
 
Transistor Link

I use metal film resistors for 1/4W, and carbon film for 1/2W. Yageo sells both at Digikey.

I source transistors wherever I can get them. It just depends on what I need. Digikey and Mouser have 90% of what I use, but it's getting harder every day.
 
Transistor Link

I use metal film resistors for 1/4W, and carbon film for 1/2W. Yageo sells both at Digikey.

I source transistors wherever I can get them. It just depends on what I need. Digikey and Mouser have 90% of what I use, but it's getting harder every day.
Thanks EW, that worked out great. Could you recommend a nice replacement
for the 2SC1124 (Q401 in the 5650 sm). Thanks:D
Klipschornman
 
B&D sells the Sony original, or you can use the Fairchild KSC2690A.
Thanks EW:thmbsp: What would we do without you.
Klipschornman
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Yamaha B-1's, B-2's, C-1, C-2, T-80, PX-3's
Klipschorns, ESS AMT-1B, JBL-L100's Large Advents, EPI
Mcintosh 2205's Mc 2100
6 channel t-amp for computer room
 
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