Yamaha b-3 service manual / schematic

Just want to change the transformer instead using the step down transformer. I know you can do it via measuring but just want to make sure the transformer rating

None schematic or service manual give this precious information , you have to use it under 100V (not 110) and make your test
No other way
 
Aloha

also looking for the B-3 Schematic or service maual cause problem with the Protection circuit
my technician needs this to fix the Amp as he said
maybe AK member of the forum here can help
ill pay for the expenses thats sure
thank you in advance
Wally
 
Hello clinic-audio!
Since I purchased a used B3, I would like to check and adjust if needed, the operating voltages.
How is the Bias and power supply voltages determined to adjust in the B3? Same like B2? I do not see service manual for the B3...

thanks!
 
I don't know if you have all the necessary tools to adjust it but I will give you the bias instructions just for check the values you get on your voltmeter

B3-bias.JPG
 
Hi Mr. Clinic-audio,
My B-3 DC offset left chanel is 324mV, right chanel is 25mV. Please kindly help me if you have information of how to adjust DC offset?
Thank you very much in advance.
 
Hi Mr. Clinic-audio,
My B-3 DC offset left chanel is 324mV, right chanel is 25mV. Please kindly help me if you have information of how to adjust DC offset?
Thank you very much in advance.
I can help you and it is the best advice no matter what anyone else will tell you :beatnik:

If you have to ask that question, please take your B-3 to someone that understands vfet amplifiers. B-3 is a wonderfully amp and you have very high chances of making the problem worse than it is. Your problem could be a very small one where you just need an adjustment, or you might need something else such as a new trim pot, and worse, a new differential input pair, which is not something easy to replace / substitute.
 
Hi Rottalpha, good day to you. Thank you very much for your advice. I understood what you mean, but here in my area I cannot find anyone can do the maintenance for this amp.
If have a simple way to check and adjust the dc offer please help me. I would like to try. Ready for the worst case already. :)
 
Hi Mr. rattalpha,
I just finished the adjustment for both bias and DC offset as per above instructions from you and Mr. clinic-audio.
Left: Bias: 42.5—>41.3mV; DC: 323.8–>11.5mV
Right: Bias: 22.0—> 41.7mV; DC:135.0–>25.5mV

It is not perfect but anyhow better than before, I think.
I used 2 volt meters at the same time and adjusted, same way with what I did when diy the V-fet amp from Mr. N.Pass before. Is it correct?
 
Hi Mr. rattalpha,
I just finished the adjustment for both bias and DC offset as per above instructions from you and Mr. clinic-audio.
Left: Bias: 42.5—>41.3mV; DC: 323.8–>11.5mV
Right: Bias: 22.0—> 41.7mV; DC:135.0–>25.5mV

It is not perfect but anyhow better than before, I think.
I used 2 volt meters at the same time and adjusted, same way with what I did when diy the V-fet amp from Mr. N.Pass before. Is it correct?

Still a bit high. Your DC offset should be as close to Zero as possible. Try to get it below 10mV at least. If you can't get it below 10mV you will first need to replace your trim pots and most likely the input differential pair.
 
Hi Mr. Rottalpha,
Thank you very much for your helpful instruction. I will try to see if I can reach the DC offset under 10mV. Actually this amp is too old so sooner or later I must have it overhauled.
 
Actually this amp is too old so sooner or later I must have it overhauled.
Hi Mr. Wu and welcome to AK,
I would comment to you that if you enjoy this amp and listen to it often, sooner would be much better than later since after 40+ years, later could easily become too late. :)
 
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Hi Mr. Wu and welcome to AK,
I would comment to you that if you enjoy this amp and listen to it often, sooner would be much better than later since after 40+ years, later could easily become too late. :)

Hi Mr. Vint Age,
Thank you for your advice. I am seeking a second one (for a spare, just in case.. ) then will proceed the overhaul.
 
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