Replace 2n3055 with MJ15003 in a MF-B1 - possible?

[Salar]

Hello, in order to raise output power, I wold like to replace the 2n3055 transistors in a Musical Fidelity B1 Amp with MJ15003.
I am aware that I would have to raise the supply voltage as well,
but besides this, will the circuitry of the B1 allow -theoretically -this mod without any further mods?
You can find the schematics of the Musical Fidelity B1in this italian forum:

http://www.costruirehifi.net/forum/v...er=asc&start=0

Any advice is welcomed!
All the best,
Salar

[ilimzn]

It should be possible as long as the heatsinking is adequate, and i have to say, MF amps from that era were not very good at that

[zoranaudio]

Yes you can replace 2n3055 with stronger MJ15003, but for what purpose???
If you want more power you can increase the voltages but that heat sinks look's very funny to me, that heat sink is for about 20 Watts of power.
That serial resistors on positive and negative reels can be replaced by good fuses.
Be careful if you buy some MJ15003, there are a lot of Fakes today.

[Salar]

Hello Ilimzm,
the heatsinking, I can work ist out. Did you look at the schematics? What about the driving transistors? Because the MJ15003 have a larger bandwith, couldnt they start to oscillate?
All the best,
Sal

[Salar]

Hi zoran,
well in order to get more power. The B1 with actually 35W clips very early with my 3A Midi master speakers, which have 4ohm.
I do not want to buy a new amp, the B1 serves me now for 19 years, that´s why I want to try a mod. The MJ15003 have a larger bandwith, could any problems arise with that?
All the best,
Salar

[zoranaudio]

Hi!
Well I understand what you really want to do with this very sexy and tiny little amp.
To be real I never tried that to replace 2n3055 with stronger and higher f max. MJ15003, theoretically should be no problems with oscillating due to wide f max of MJ15003.
You have to try that your own or wait for somebody who's done it before.
In my DIY amplifier I am using 8 transistors per channel 4x MJ15003 and 4XMJ15004, and I got some bad work and oscillating with input circuit TL071, when I replace with 741 op. amp my amp. finally works all O.K.
Also you should take care with previous transistors on this amp I mean maximum VCE , I took a short look on that schematic and there are BD139/140, in my amp this tr. are BF469 & BF470 which should have a more wide frequency range.
Everything depends on the supplied voltages to the amplifier.
In My amp supply voltages are +72 0 -72 and I have no problems at all since I made it about 1and a half year ago, It is every da in use approx. 24 hours a day.
That resistors of 0r47 ohm live in place I looked carefully , this is for further filtering the power supply, so they have now also a fuse work if something goes wrong with the amp.
The place looks very small if you want to add some bigger heatsinks or bigger toroid, but if you are able to do something than just try it.
I wish you good luck.
If that amp was mine I would not touch anything.
Cheers.