Thanks!
I have 4 more usable 2SK180 to get another B-1 working if 1 should find its way to me ...
I am hoping to find one that does not need them
Yamaha B-1 restoration/repair
- Thread starter vintagejapan
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- 2sk180 2sk77 v-fet yamaha b-1
I am hoping to find one that does not need them
I just took another look at the data sheets. I had forgotten that it's the 2SK77 that actually has the higher input capacitance ...
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Nick, in our correspondence you mentioned that resistor value changes on the driver board were needed when using 2SK180's to replace 2SK77's which are lower Mu devices. Would you mind sharing that information in this thread?
ilimzn
Well-Known Member
Not so sure, I seem to remember my measurements had the 2SK180 higher, possibly because the tables seem to show different measuring conditions. It all looks very similar, though.
I measured at Vds=0V and Vgs=-0.5V which is practically worst case (the source-drain channel to gate 'diode' behaves much like a large varicap diode so the capacitance is highest at lowest voltages).
@ants2au, 500pF is not too signifficant as we are talking around 3nF, in fact it would be close to tolerances between the same nominal VFET. Less capacitance is desirable.
However, it is the difference in mu and the actual curves that require adjustment to the bias and balance range. Don't have the B1 schematic close by but if I recall correctly it's the values of resistances around adjustment trimmers that need changing (perhaps trimmers themselves).
I measured at Vds=0V and Vgs=-0.5V which is practically worst case (the source-drain channel to gate 'diode' behaves much like a large varicap diode so the capacitance is highest at lowest voltages).
@ants2au, 500pF is not too signifficant as we are talking around 3nF, in fact it would be close to tolerances between the same nominal VFET. Less capacitance is desirable.
However, it is the difference in mu and the actual curves that require adjustment to the bias and balance range. Don't have the B1 schematic close by but if I recall correctly it's the values of resistances around adjustment trimmers that need changing (perhaps trimmers themselves).
As ilimzn says:
In a nutshell, along with a few other things Vgs is extrapolated from the 2SK180 curve set at the same operating point as where the 2SK77 is biased and then some calculation are made around that.
vintagejapan
AK Member
After a few weeks the B-1 fitted with the 2SK180's is singing along really well. I fired up my other B-1 that has all original outputs and to my years the 2SK180's sound a smidgen more extended on the highs. I must honestly say can only notice when side by side.
I am thinking to resurrect a 3rd B-1 that I was keeping for spare parts. On the power board #2 have a couple of bad transistors.
2SK1447
2SK1448
and MPSU60
Got new original replacements for the mpsa92 and mpsa42
Looked around for 2SK1447 and 1448 but could not find anything. Will a TIP47 be a replacement for the 2SK1447?
I am thinking to resurrect a 3rd B-1 that I was keeping for spare parts. On the power board #2 have a couple of bad transistors.
2SK1447
2SK1448
and MPSU60
Got new original replacements for the mpsa92 and mpsa42
Looked around for 2SK1447 and 1448 but could not find anything. Will a TIP47 be a replacement for the 2SK1447?
vintagejapan
AK Member
The other mod I did on this board is to move the 10uf cap that gets a lot of heat on the other side of the board
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vintagejapan
AK Member
Still pondering on the power supply board #2
Found out that the original mpsa42 transistors have much lower hfe from the new ones I got, so the -200V cannot be adjusted at all!
The -200 goes up to 230 after power up and then is not steady, slowly declines under 200
Still looking for MPU60 and the 2SK1447, 2SK1448
Found out that the original mpsa42 transistors have much lower hfe from the new ones I got, so the -200V cannot be adjusted at all!
The -200 goes up to 230 after power up and then is not steady, slowly declines under 200
Still looking for MPU60 and the 2SK1447, 2SK1448
clinic-audio
all on YAMAHA untill 1990
Hello Vintagejapan
I have refixed 3 B1 in 2015 and will do 5 in 2016 . It is a very long process to do but all were working well with 100% original V-FET and my electrolityc PCB kit to improove reliability of this amp and avoid dammage on power V-FET when one 15000MF/100V is bad and may destroy output V-FET .
I never saw any 2SK1447 or 2SK1448 in a YAMAHA B1 ! are you sure it is not 2SC1447 and 2SC1448 ?
I have refixed 3 B1 in 2015 and will do 5 in 2016 . It is a very long process to do but all were working well with 100% original V-FET and my electrolityc PCB kit to improove reliability of this amp and avoid dammage on power V-FET when one 15000MF/100V is bad and may destroy output V-FET .
I never saw any 2SK1447 or 2SK1448 in a YAMAHA B1 ! are you sure it is not 2SC1447 and 2SC1448 ?
vintagejapan
AK Member
Hi clinic,
Yes my mistake. 2SC1447 and 2SC1448
Nice capacitor pcb kits!
I would love to get a couple of those if you have spares
I made a replacement of the big caps myself with 8x10000 Elna caps but does not look as nice as your kit.
vintagejapan
AK Member
This is the board.
clinic-audio
all on YAMAHA untill 1990
Yes I worked months on this kit and wait 9 months to get capacitors made for me . This is the only serious way to keep your B1 working for years trouble free . You can buy mine or the one made by Vint age .( I bought 3 from him ) because my suppliers delay was too long and customers don't like to wait and I can say it is very good too ! I know because I have tested them in real conditions !
I have spares kits, yes ! my kit is PCB + 4 Capacitors
Thank you clinic! Yours does look very nice and maybe it might be a little easier to fit in than mine¿. You will have to send me one to try.
Mine uses 4 18000 uF/100V 105° C caps but 85° C caps will also work since they are located away from the heat.
I think we love the B-1 more than most to go to so much trouble to make them work for many more years.
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vintagejapan
AK Member
Well, I feel spoiled for choice 
I guess I can have 2 of each? Do both come with the caps? And what about $$
So no luck with the transistors? I tried MJE15035 also instead of 2SC1447 but was not suitable
I guess I can have 2 of each? Do both come with the caps? And what about $$
So no luck with the transistors? I tried MJE15035 also instead of 2SC1447 but was not suitable
vintagejapan
AK Member
What caps are you using in your kit Vintage?Thank you clinic! Yours does look very nice and maybe it might be a little easier to fit in than mine¿. You will have to send me one to try.
Mine uses 4 18000 uF/100V 105° C caps but 85° C caps will also work since they are located away from the heat.
I think we love the B-1 more than most to go to so much trouble to make them work for many more years.
vintagejapan
AK Member
And yes, I do love the B-1. I have come across and own few other pieces but still keep coming back to the sound of B-1.
To my ears it does sound sweeter than my other monster MX-10000 although the MX-10000 can drive anything with ease
To my ears it does sound sweeter than my other monster MX-10000 although the MX-10000 can drive anything with ease
Mine uses 4 18000 uF/100V 105° C caps but 85° C caps will also work since they are located away from the heat.
I would love to experience the sonic beauty of an MX-10000 ... but there's something about the B-1 and B-2 that keeps me coming back for more and more and more.
vintagejapan
AK Member
Sorry I meant to say what brand on the caps?
About the MX-10000. It has 'balls' and stamps its authority, can also be delicate, although my personal preference on the high frequency is the B-1. Guess it really depends on what genre of music.
About the MX-10000. It has 'balls' and stamps its authority, can also be delicate, although my personal preference on the high frequency is the B-1. Guess it really depends on what genre of music.
