yamaha B4 B5 amplifer Vintage

[muddasirwaheedmalik]

hi there , a pair of Yamaha B4 and a pair of Yamaha B5 amps are avialable for sale. B4 is 120 w/ch and switchable to 30 w/ch using VFETs.

the B5 is 240 W/Ch also using VFETS known for good warm sound.

I am currently running KRELL KRC-HR preamp +KRELL FPB 600.All class A but honestly a bit sterile in mid range with B&W 802.

My question is that for argument/experiment sake should i biamp B4+B4 class A i.e 30 watt mid, and 30 watts bass bins. or B4+B4 30 watts class A mid+120 Watts bass bins or bi-amp B4+B5.

Its on a used flea market and going around 300-400 USD per peice so cannot audition them without buying them. Please dont throw the question of replacing KRELL with yamaha its just vintage collection , good looking pair or the pair could be used "some day " with class A warm sound for some full range or horns.

Any one having experience with these Yamaha B4-B5 ?? BTW sounded nice in the flea market noise on some pro speakers .
Any

 

[muddasirwaheedmalik]

BTW VFETs as i know were early made in 1970's and 80's and were very expensive at that time. known for warm mallow sound , not SS but discontinued for cheaper power bipolars in late 80's. not available anymore easily. (one of the reason for my attraction for it)

 

[muddasirwaheedmalik]

ITs front end it fully regulated, By pusing the Class A button the voltage rail drops from +/- 72 Volts to +/- 36 volts ,incresing bias current through a relay mechanism and hence increasing VA stability or Pseudo-regulation. supposed to give better sound for less wattage application. the Vfets are 2SC2460B 2SA1050B pull push pairs on each side.

 

[muddasirwaheedmalik]

some thing special ..its all Dc coupled like krell and that B5 have 22000uf 100v capacitor pair for regulating 240 Watss of output. it quite something if i compare it to krell FPB 600 with bank of 4x6800uf on each side.

 

[pieter t]

ITs front end it fully regulated, By pusing the Class A button the voltage rail drops from +/- 72 Volts to +/- 36 volts ,incresing bias current through a relay mechanism and hence increasing VA stability or Pseudo-regulation. supposed to give better sound for less wattage application. the Vfets are 2SC2460B 2SA1050B pull push pairs on each side.

Please note that the only Yamaha power amplifiers using VFets were the B1, B2 and B3.
The amplifiers you offer for sale have no VFets but Bipolairs when I am right.

 

[muddasirwaheedmalik]

ok, i read about B2 and i thought it may be true for the entire B series. would have to check. BTW any comments about SQ of B4 and B5 amplifiers.

 

[pieter t]

No comment on B4 and B5.
I own a Vfet B2 which I like very much.

 

[muddasirwaheedmalik]

does it also also has class A operation button. ? If so do you indeed hear sonic difference and BTW what speakers are u using with them.

 

[pieter t]

does it also also has class A operation button. ? If so do you indeed hear sonic difference and BTW what speakers are u using with them.

No, the Yamaha VFet power amplifiers had no provision to switch them to class A.
I use my amp with Yamaha NS1000 loudspeakers.

 

[muddasirwaheedmalik]

Nice setup. Thanks for input. any one else having any reviews about B4/B5