'73 MKii Superlead bias issues

[Reeltarded]

http://home.comcast.net/~mamp17/1959%20Layouts.html


^^^^

Does that help?

[flintrock]

That looks like a winner! Will let you know how it goes.

[flintrock]

Actually that schem looks quite a bit different. Some of the wiring goes to the board first then back to the switches.

[Reeltarded]

Yes but look at the paths. If you draw out what your circuit looks like and just the part you need from the other it will make a bell go off in your head.



It's one of those things. Make sure you have color codes for original transformers as some do vary.

[flintrock]

Okay, I am done rewiring the power switch and removed the polarity switch from the circuit. Orange wire goes to mains fuse along with the neutral according to the schematic. Is that ok for the mains fuse to not be on the live (black) wire? Doesn't seem to be an issue to me since orange should be the common wire but just want to verify its ok to run without a fuse first in line, but since its ac shouldn't matter right?

[Bob S]

I'd definitely put the fuse in the hot (120vac) line.
Otherwise if you get zapped between hot & ground (it will happen sooner or later), the current limiting device is in the breaker box - not the amp.
Be Safe !
I'll let the Marshall gurus help with the debug - sounds like you're almost there.
Good Luck,
Bob

[flintrock]

Got the '73 fired up today. Plate voltage at 502 with 37-79ma bias range. Should I treat KT77's like an EL34 or at its actual 70% dissipation? I'm thinking in the middle maybe as long as the PT can handle it which I don' t really see as a problem.

[flintrock]

Biased in at 37ma, really about as low as it will hold without further bias resistor changing. Seems to play just fine at this level, and my god this amp is ridiculously loud!!