Yamaha B-1 Alert

[Elroy]

Yamaha B-1

Looks nice it's a 240V though. Guy said he pugged it into US 120V and powered it on, could that be a problem?

 

[sol7]

Better to plug 240v into 120v (fairly harmless for short duration) than 120v into 240v (smoke cloud).

 

[avionic]

Yamaha B-1

Looks nice it's a 240V though. Guy said he pugged it into US 120V and powered it on, could that be a problem?

In this case most definitely could have cooked the VFET's..:scratch2: Not enough pinch-off voltage from the -200 volt power supply. Might have gotten lucky and the VFET protection circuit may not have allowed the B+ and B- rail voltage to get to the outputs and prevented a catastraphe.

 

[avionic]

Better to plug 240v into 120v (fairly harmless for short duration) than 120v into 240v (smoke cloud).

True if you were talking about a bipolar transistor. VFET is a whole different can-o-worms.

 

[Elroy]

That was what I was wondering about- the VFETS. Why would anybody in their right mind take that kind of chance w/ a B-1? :headscrat

 

[theophile]

That was what I was wondering about- the VFETS. Why would anybody in their right mind take that kind of chance w/ a B-1? :headscrat

Stupidity exhibits no hesitation.

 

[Elroy]

"I have not tested it other than powering it on with the standard 120 U.S. voltage, and you can hear it power on, and it is sold as is."

That last phrase "and it is sold as is" placed on the end of that sentence is a red flag to me. He isn't verifying that it in fact works and he is saying sold as is. He leaves you w/ no choice but to consider it a parts unit for bidding purposes (unless you feel like gambling). They are worthless w/o ALL the VFETs working except for hopefully salvaging whatever VFETs that still may be good.

 

[suspect]

i cant tell you anything about the voltage but i can tell you i know the seller personally...cant say were friends but i know the guy...i'll tell you this much...this came from a local swap meet.

 

[Yggdrasill]

I always assume that the seller, unless they're an idiot, incredibly lazy or both, knows whether something is working or not. I think that most folks, if they had a unit like this, would find a way to hook it up to 240 volts to test it as it's sooooo much more valuable if you can verify it's working.

To my mind the most likely scenario is that the seller hooked this up to some speakers, turned it on, and heard well, whatever you hear when vfets blow. Heck I didn't know that low voltage could blow those, though I would never have taken the chance. Then he quickly posted it as he did, with his fingers crossed.

Can't blame him, his ad is not misleading in any way. But it screams CAVEAT EMPTOR!

 

[avionic]

the VFET protection circuit

When going through these 100lb beasts. First discharge power supply caps. Next remove all four FET's.Then there is a lengthy procedure to first check and adjust the -200vdc PS,12vdc power supply,and the +/- 25 volt supply.Then about 3 pages of checks to do to verify the rail power supplys to the FET's shut down in controlled manner to prevent damage to the VFET's in case of a failure,Last page you finally install the VFET's to set the bias. I've really over simplified this overview and would highly recommend that any repair work be defered to a tech with VFET experience.

The last B-1 I worked on. Had a shorted TO-3 switching transistor which would have fried a FET in a failure condition. BTW..Low mains voltage is considered a failure condition!

 

[Elroy]

Yeah, the B-1 is the heaviest amplifier I have ever lifted. Do you have one Avionic? I had one for a short while and just didn't want to invest the money it would take to bring it up to snuff. Sold mine to MarkB years ago.

 

[walkandtalk]

 

[avionic]

Yeah, the B-1 is the heaviest amplifier I have ever lifted. Do you have one Avionic? I had one for a short while and just didn't want to invest the money it would take to bring it up to snuff. Sold mine to MarkB years ago.

I have one on the bench.Not mine.I don't personally own one.But have serviced a few.

 

[cdfac]

one can just hope that the VFETs never saw any significant voltage. the protection circuitry is pretty thorough, although i don't think this is one of the conditions that is specifically protected against.

 

[avionic]

one can just hope that the VFETs never saw any significant voltage. the protection circuitry is pretty thorough, although i don't think this is one of the conditions that is specifically protected against.

Should be...90% of the problems I am finding with these are the protection circuits.:scratch2:

 

[cdfac]

Should be..Thats one of the check out tests is to vary the input AC.But..90% of the problems I am finding with these are the shut down circuits.:scratch2:

good to know, on both accounts.

 

[theophile]

Would buying with Paypal protect the prospective purchaser,in the event that it doesn't function?

If I was a prospective buyer,I'd be asking him whether it works. :yes:

 

[mackat]

Why can low into high fry, but high into low don't?

 

[theophile]

Why can low into high fry, but high into low don't?

Nobody said that.

The 240v B1 will potentially be damaged by 120v or 480v,if as Avionic stated the protection circuitry is unable to protect the v-fets.

The ideal thus, is to only use your v-fet amp into the line voltage stated on the compliance plate.

The moron who is selling the B1 which is the subject of this thread,should be horse-whipped.

 

[mackat]

Oh, okay. I don't know much about transistors.