OT:Could someone tell what's going on in this amp schematic?

[Chris Goodson]

What's the deal with the .05 cap?  Is it coupling the 1st and 2cnd stages?  Why is it connected to the input jack?http://www.tubefreak.com/mb1pre.gif

[Peter Snowberg]

When you plug into that lower jack, a switch inside the jack is closed which connects the first tube stage to the second via the 0.05uF coupling cap. If you plug into the top jack, the first stage is unconnected so that it doesn't add any noise.

take care,
-Peter

[RedHouse]

Yes, it's a "coupling " capacitor.

[nirvanas silence]

Exactly, its a "Hi" and "Lo" inputs.

[Brian Marshall]

yep, i hate it when ppl draw stuff up like that to fit in a neat little space, instead of making it messy, but obvious.

[puretube]

how else would you draw it: explain on the right side of the 1st triode, that the switch is part of the input-jack?

to me, that drawing is the best self-explaining way to show a Boogie...

[Chris Goodson]

I kind of figured it was something like that.  I've never seen a jack like that though, is it "normally open"?  
I'm just trying to figure out something to do with my Bassman's bass channel since I never use it.  It's got an extra 1/2 tube in there that's not being used for anything and I though some sort of high-gain thing might be cool.  That Boogie schematic seem's to be sort of close to what's already in there, if I understand correctly the first Mesa amps were modded Fender's.

[Peter Snowberg]

Just duplicate the first preamp stage in front of the existing first stage and couple them with a small cap and you'll have the basic Boogie idea. Try values from .001uf to .022 to start with.

I've seen jacks for sale with an insulated switch, but I've never shopped for one. I know there are plastic enclosed jacks that have that feature.

Take care,
-Peter

[puretube]

yep, and don`t under-estimate that little (switched) 220k at the top jack!
watch your routing! -feedback/squeeling danger- !
those double switching jacks often require to drill the mounting hole
2mm wider...

boogie, chillun ...