2. amps-preamps
  3. 140506-84640

2 different Bedini 150/150 Mk II Amps

I was comparing the insides of another Mk II with mine and they are really different. The first one is like my old one with no markings on the transistors. John Bedini was supposed to do some kinda voodoo inside them to work his magic. I remember this detail because my ex-girlfriends daughter cooked that amp 30 years ago by playing it all day at max volume when she was staying home from school one day. My repairman was never able to get any details on those trannys so the amp was never repaired. I guess we can't post pics so I'll just have to describe it.I purchased a different new to me B150MkII recently and the insides are really different. All the trannys are labeled Made in Mexico and there are 4 new ones on the circuit boards along with other different components. The other amp didn't have these 4 extra ones or slots to install them. Everything in my amp looks very fresh and new although it could be just well kept. It sounds fantastic.
I figure there are 3 possible scenarios with my new amp:1.I had read that John Bedini had modified these amps during the run so perhaps I have a later version.2.I had read that JB also would do mods for you when you sent it in for service.3. A really skilled tech modified this with a new design and new circuit boards which I doubt.
Is there anyone out there who could help me out.Also the only thing wrong with mine is the little light in the power switch doesn't work or will sometimes flicker. I can't find the direct replacement so if anyone knows a source could you please let me know. ThanksBobber


skeepowder
robertgalka's avatar
robertgalka
5 posts
 
My tech repaired my 250/250, he said it was the input differential amps, whatever that means? He had to replace four transistors that were matched.

I've been using it for a while and it runs really cool, maybe 105 degrees fahrenheit on one side, and 100 on the other. Aren't they supposed to run a lot hotter? Should the bias be increased?


atmasphere's avatar
atmasphere
11,575 posts
 
Sounds like it to me.
robertgalka's avatar
robertgalka
5 posts
 
I turned up the bias so the transistors are about 125 f and the fins are about 105 f. I'm not sure how high I can go? I read that it should run hot enough where you can only hold your hand on the fins for about 5-10 seconds. I have a long way to go yet.

This is what I found by searching the web, "Re-Set Bias to 35 Ma across emitter resistor Positive Side". This was written by John Bedini. I always thought current flows through a resistor and so positive and negative shouldn't matter? I have no clue what an emitter resistor is.
atmasphere's avatar
atmasphere
11,575 posts
 
You have to be careful here- when the amp is one taking any readings in it can end in disaster if a probe slips! These instructions make perfect sense to a qualified technician- which is where you should take it!
minorl
1,014 posts
 
The instructions make very good sense and are correct for that amp. You either need the schematic or if you understand circuit design and layout, you can see clearly the emitter resistors.  However, since, you don't know an emitter resistor from a carburetor, I would suggest that a qualified technician is the way to go. 

that is a nice amp.

enjoy 
More to discover