• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

bogen MO100a monoblocks overhaul

I just verified my transformer is good, so thats a good thing. I got to looking at the bias supply on this, and its kind of clever. Instead of a dedicated bias winding, it picks up some AC off the B+ primary via a 0.47uf cap and feeds that through a diode and some filters to make the grid bias supply. I thought that was sort of a novel way of doing it and it gives me ideas if I wanted to convert something to fixed bias without having a transformer that has an extra winding available.
 
I thought that was kind of cool too. I have to admit I hadn't quite put it all together until you explained it.

I just did the conversion to stand alone status on my second unit to see if it was good. It has a really bad PS cap - talk about noisy:thumbsdn:.

It satisifes me that my transformers are good on it, so I am going to go ahead and tear it all the way down as well for the same overhaul as the first.

I still need to figure out what to do with hte extra holes on the deck on the left side.

Till later,
mark
 
I didn't try to power mine with tubes. The caps didn't get hot, but thats all I know. It had mismatched tubes in it, and there is some damage underneath. It had two 8417's and two 6L6G's in it. The bias balance pot looks like it caught fire and at least one of the plate resistors is completely smoked out. Its almost like you can't feed 600 volts to the plate of a tube rated for 360. I wonder if those 6L6's are fatally wounded.
 
I own bricktop's Mo-200a that runs KT-77's in the blumlein auto bias scheme and it is fantastic! 65 watts of clean, crisp sound. I have the high Res schematic if you're interested.
 
kpaxfaq -- Is that power rating per channel within one MO-200 rigged for stereo or the total power of both channels together -- or is that the power of the dual quad of tubes from a single MO-200 still rigged for mono?

Dave
 
65 solid watts per channel from tubes ain't bad.

Looks like I've got a line on another with good 8417 tubes, so I guess I'm going that route. Even if its not 100 watts anymore, I'd be plenty pleased with 60-75 of clean power. Thats triple or more what I normally run.
 
kpaxfaq said:
I have the high Res schematic if you're interested.
Click to expand...

I'm interested in your high Res schematic, would a tweak on FZ's stosh seal the deal.
Curious as to what Dave is diggin' at, which just might get us close to the crux
of the biscuit. Your schematic would be most humbly appreciated. Thanks XXX
 
You must log in or register to reply here.
Back
Top Bottom