B2

Changes in build quality in Omron Relays thru the years, the one on the left was a service replacement supplied by Yamaha early 80's for the B2 and the one on the right purchased on line 2015
 

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  • Original 1979 Omron LY2-0  12v on Left and 2015 version on right .JPG
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Changes in build quality in Omron Relays thru the years, the one on the left was a service replacement supplied by Yamaha early 80's for the B2 and the one on the right purchased on line 2015

Too bad there isn't a solid state substitute relay out there to replace it with. Old or new, eventually those contacts become an irritation ...
 
Yes very true Vintage solid stage is the way to go.
I may have mentioned this before but it wont hurt to repeat this :
I’ve observed quite a few B2,s with the Power Supply Board scorched in the area of
R234 and R234 feed , metal oxide resistors. It may be prudent to replace these and leave longer legs so as to have these sit proud of the PCB to slow any further degrading of NA06749. If these PCB’s get scorched excessively it may cause breaks in the tracking.
 

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We have a member,Timo chasing a vol pot for the B2, has anyone fitted a recent manufactured Vol pot as a direct replacement to a B2
Any clues guys for this member ?



Quote from Timo , ”Haven't found out about replacement pots yet. Do the originals still exist ?
I would like to keep it original, and with my meager skills, I might be able to do the pots myself.
Cheers, Timo.”
***************

Can anyone provide an answer to the above question that was asked back in 2014? I am in the position now of having to replace my speaker A volume controls. B is ok and that is what I am using but A feels and sounds like there is gravel inside. Is there a quality drop in replacement?
 
CTS 1/4W Series 270 16mm 25K Log Taper
Digikey #CT2239-ND
Mouser #774-270X232A253B2A1
Mfg. #270X232A253B2A1

Knob
Kilo International OEJ Model Matte Black
.125" (3.18mm) shaft .5" Dia
Digikey #226-4084-ND

The knobs have to be changed for these pots, so you'll need to do all four of them. The new knobs look nice. Not perfect, but I've had to replace the stock pots on nearly every B-2 I've worked on, and not one owner has complained about the new knobs.

The legs of the pots have to be spread a bit to fit the holes, but it's not a big deal.
 
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Excuse me for butting in …..Echcowars that’s very good info and thanks for sharing this,
I know this would be run of the mill job for you but in your opinion would a owner with only meagre skills be able to accomplish this job.
Is there any shaft cutting of the pot ?
 
Yes very true Vintage solid stage is the way to go.
I may have mentioned this before but it wont hurt to repeat this :
I’ve observed quite a few B2,s with the Power Supply Board scorched in the area of
R234 and R234 feed , metal oxide resistors. It may be prudent to replace these and leave longer legs so as to have these sit proud of the PCB to slow any further degrading of NA06749. If these PCB’s get scorched excessively it may cause breaks in the tracking.
Yes, replacing with longer legs resistors will help but it does not change the fact that heat rises and the PSU board acts as a heat trap.
 
CTS 1/4W Series 270 16mm 25K Log Taper
Digikey #CT2239-ND
Mouser #774-270X232A253B2A1
Mfg. #270X232A253B2A1

Knob
Kilo International OEJ Model Matte Black
.125" (3.18mm) shaft .5" Dia
Digikey #226-4084-ND

The knobs have to be changed for these pots, so you'll need to do all four of them. The new knobs look nice. Not perfect, but I've had to replace the stock pots on nearly every B-2 I've worked on, and not one owner has complained about the new knobs.

The legs of the pots have to be spread a bit to fit the holes, but it's not a big deal.

Thanks EW!
 
Hope this helps.
There is not much to accomplish this if you have a screwdriver and a soldering iron.
You need to remove the front plate and the rest is sef explanatory. The pot boards are modular, as you can see.
 

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interesting read translated from japanese
YAMAHA
B-2 NATURAL SOUND POWER AMPLIFIER ¥ 200,000
stereo power amplifier that Yamaha was released in 1976. 1973 equipped with its own development of the SIT (V-FET) crossbow class power amplifier of all FET B-1 was released the company, V-FET Anne was developed and launched in a more realistic form was a flop. In the B-2, the power FET · 2SK-77 that has been developed in the B-1 one size to small, was complimentary of, Shinkai of onset power FET · 2SK-76 (Nch), mounted 2SJ-26 (Pch) It had been. V-FET is, the three-pole vacuum tube by the voltage control element that operates similar also, it was element with a different again appeal to the MOS FET. However, at that time in the technology of mass production, it was what produced of the combined pair characteristic is difficult.
Yamaha, Pch, Nch of device chip size of the impurity concentration, the fully discussed in the gate mesh structure addition, strictly control the production process it is possible that, combined pair characteristics over a wide operating range, still own a pair of sorting in a way, it was selected "Yamahasu was using as Papea FET ". As a result, in the B-2, the first FET complimentary push Yamaha pull configuration has been taken. Excellent linearity of the newly developed, by using a sufficiently high FET gain, can be driven with low power, the driver simple circuit configuration of the stage previously stable NFB is applied two-stage amplification had been taken. Also, Karentomi distortion generated such as by being a whole page except the combination sulfonate and the first stage of the color circuits in a push-pull configuration, lower can be suppressed, excellent bare properties and by being implemented and superior while applying the least the NFB distortion rate characteristic is secured had been. In addition, eliminating the capacitor from the NFB loop, complete DC was also removed to the capacitor of the input it had become an amplifier configuration. The output stage, pure complimentary parallel push using two Yamaha original super pair FET was configured with pull OCL circuit. The power FET is a drain loss 100W, linearity is well pairs especially the ones that have all of the well, a wide output range, had obtained a low distortion in the frequency band. By the this is excellent FET Ri, it had been operating at low idling current to break the common sense of it until the FET amplifier. The heat sink large to also be used for the Lch, respectively Rch, the power FET is mounted directly to a heat sink which has been subjected to special processing, heat by lowering the resistance effective heat radiation is performed, with a sufficient margin even at full power It was possible the operation of. This drive circuit to drive power FET, Symmetrical push-pull drive scheme has been adopted directly below. This is, of the power stage Nch, Dora in the Pch of FET each pure complementary push-pull circuit in a luxury circuit that Eve, had contributed to the excellent characteristics. As described above, the rising, the pairing with the excellent power FET to linearity, Symmetrical push-pull times by the road, and high slew rate, we have realized a low distortion. The voltage amplification stage, the first stage in the cascode bootstrap with FET differential amplifier, current mirror differential in thepre-drive stage and had adopted a push-pull amplifier. In the first stage, the super-low-noise FET which precisely align the
pair characteristic, and coupled to a thermal and a differential amplifier had been. Using the high-gm FET, is multiplied by a constant current bias in which the temperature correction to the source side, common mode rejection suppress the drift of the midpoint potential to a minimum by taking very large ratio (CMRR), also, of the power supply shadow of slight ripple sound also been canceled, it has secured a high SN ratio. The differential amplifier stage, is equipped with a cascode
bootstrap circuit, a drain in the change of the input signal - voltage between the gate and so does not change the input impedance strain were not to deteriorate vary. Puridorai parts and to the class A operation in the differential push-pull of a combination of current mirror circuits, enough gain in the low distortion had been. Power supply circuit, in the same manner as the B-1, is equipped with a power transformer in the left and right independent, was to avoid the mutual interference between channels.
Use the large capacity Chemi-Con of 18,000μF × 2 per one channel, it had to achieve a richbass characteristics. Further, the drive stage before a complete constant-voltage power source, to suppress the deterioration of S / N due to external noise and ripple, amplifiers times it was to ensure the stable operation of the circuit. The bias circuit of the power FET, a change in the bias voltage caused by fluctuations in the power supply voltage automatically corrected to
it had always adopted the automatic stabilization bias circuit to keep constant. Also, by using a diode matrix, POWER I was so prevent damage to the FET by preventing rush current flowing to the switches turned ON FET. Peak level meters, the same as the UC-1 adapter for the B-1, -50dB from (1mW) + 5dB (300W) Madere can be displayed without Nji switching, instruction within -2dB also a sine wave 1 wave of 10kHz high-precision logarithmic compression type Pikume entering the
error Ta had been installed. This meter, "EXTERNAL" so that it can be used in other applications as well as power display switching between "INTERNAL" is provided, in the "EXTERNAL", had also become possible use of the meter alone. Other Me, such as when the multi-amplifier, you can look at the output level of the other power amplifier, that you can see the input voltage of the preamplifier I can also be used to. Speaker output A, provided two systems of B, not only can be switched at
the front panel, the level of A, B2 system left and right had become can be adjusted at the level volume independently. Input There is also a 2 system, which is also the front panel had become can be switched in. As described above, B-2 is, as FET power amplifier next to Chodokyu machine B-1, I met only new, care about in all FET is such as using a bipolar transistor and a hybrid not, has become a balanced design, as at the time of the amplifier physical properties also had what was very good. Also towards the sound, but strength is not enough B-1, the unique V-FET was delicate and amplifier of nuance rich attractive sound.
 
For collectors, the original B2 Owners manual not a copy, is available on a German website
'Spring air de' albeit expensive
 
The thing is even if these were the real thing you'd need more than 8 to do proper matching unless you were real lucky. Back in the day Yamaha hand selected them in matched pairs for the B-2/B-3.
 
So, been here nine years to read and read some more. This, my very first post! Please help and forgive me for my lack of knowledge. I do know what sounds good.

My beloved Yamaha B-2 developed a low hum noise and took it to "the man" in Glasgow to fix it and service it. After six months, I got it back but with the two 2SK76's removed as he says he couldn't get the bias right. Now what do I do? I found these advertised via a google search in China. Are they really a total waste of time and money? Here below, are a couple of links;

https://www.yoycart.com/Product/547298071515/

https://www.yoycart.com/Product/556844634542/

https://www.yoycart.com/Product/557709741799/

https://www.yoycart.com/Product/547253917115/
 
Are they really a total waste of time and money?
Yes.
Sadly your story isn't uncommon, happened to a guy's B-2 local to me just a month ago. Basic story is "take amp to repair shop not specializing in vfets, amp blows up through tech's own fault, amp is blamed and held hostage for a long period, before finally being returned much worse than it went in".

Not many people will have vfets just sitting around to sell, one of the few people I know who has legitimate ones is @clinic-audio on this forum who you can contact via PM. They won't be particularly cheap but at least you know they're genuine.

The bigger concern is that if someone's pulled vfets out of your amp (for any reason other than straight theft), then there's a very high chance that there's further damage to the amp, and that fitting the new vfets alone will probably just kill them too. You also need to verify what's in the amp is still alive - the 2x 2SJ26 in the bad channel need to be tested (ideally with a curve tracer), and if you work with clinic I presume he would ask you to at least send those two to him so that they can be first tested, then matched - since the J26/K26 were matched both in complement and in parallel (so replacements ideally should be too). Personally I would be having all of the remaining vfets tested, and the entire amp gone over before re-fitting them.

At this stage you really need someone who has experience with these particular amps to go over it and repair any damage that was done before fitting the new output transistors.

Obviously it may also be worth comparing the price of a working replacement amp, or a functioning parts unit from Japan. Best wishes moving forward and sorry to hear what happened.
 
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