Musical Fidelity B1 MKII

[Herr Zpy]

Hi!
After 14 years I finally got one.
After set it up on my living room, the problems started:
- Sound distortion
- No heat

Small adjustments on the right pots of each channel:
- No distortion of sound
- Normal temperature
- A "thump" sound when the volume is off

Bigger adjustment on 4 the pots:
No distortion.
Overwhelming temperature on the Toroidal
The first 2n are hot the next 4 are burning and the final 2 are cold.
After 2min the amplifier shuts down and the fuse is blown.

Saturday I went to 3 electronic houses to see if anyone could help me with this problem and all of them said NO, of course with various reasons to that.

Should I change all of the 8 2n's?


Thanks

 

[nigelwright7557]

You need to find the manual for setting up the pots properly.

Too much bias could end up frying the amp.

With age its usually the electrolytic capacitors that go or deteriorate.

I would get the amp working first before making any changes.
Then change one thing at a time so you know what has made a good or bad difference.

 

[jaycee]

It sounds like you have some transistors failed and they are causing a heavy load on the supply. It looks like someone already did replace them - MF usually rebrand the transistors. You may be better using some more rugged transistors like MJ15024/5 or MJ21193/4.

Chances are the driver transistors also failed. These amps are not really well designed to be honest - those heatsinks are far too small.

 

[Herr Zpy]

Hi!

First of all thanks for your help.

I bought it having in mind a nice overhauling, like changing all the capacitors and resistors by audio-grade ones. Also I will change the opamp.
But it should have arrived in working condition. Now it´s a problem that I don´t have the proper knowledge to deal it.
I´ve already ordered most of the caps, and I'm looking for the so called Rugged transistors.