Vox AC 100/2 schematic and some questions

[Willabe]

Ok, so we are talking about an AC100 with 4xEL34's.

 

[pompeiisneaks]

yes but I'm still unclear on what pin you're referring to as missing a resistor.  I've got resistors on two of the three, and the third goes to the B+...   I think I'm okay per what Sluckey said because some amps don't have resistors on that grid, one being the AC100 and one other right?

~Phil

[Willabe]

yes but I'm still unclear on what pin you're referring to as missing a resistor.  I've got resistors on two of the three, and the third goes to the B+...

The screen grid/grid 2, the grid that goes to the B+.

Grid 1 = control/input grid, grid 2 = screen grid, grid 3 = suppressor grid.

I think I'm okay per what Sluckey said because some amps don't have resistors on that grid, one being the AC100 and one other right?

No.

Sluckey use screen R's on his builds too. (I took his comment as saying I didn't explain to you clearly about screen grid R's and why to use them.)

Power tubes need screen grid (grid 2) resistors to limit the screens current. (With EL34's you can start with at least 100 ohms and go up as much as 1K for a screen grid R.)

A lot/most of the old amps didn't use screen grid R but later on they realized they should and most if not all amp makers started to put them in. 

The control grid (grid 1) should have a 'grid stopper' on it.

Suppressor grid (grid 3) is usually internally tied to the K and you have a 1 ohm R on the K going to ground to measure the EL34's current draw to be able to set the -bias.

[pompeiisneaks]

Ok sounds good, I'll add 1k resistors there, is 1k fine for the two per pair?  Each half of the power tubes pair has a line going to B+, do I put 2k per pair or just 1k total?  I'm getting pretty close to building this thing and I want to be sure I'm doing it right. Thanks so much Willabe.

[Willabe]

You need 1 for each tube.

The larger the value the more the protection but the more compression it will add when the amp is turned up loud.

If you like that great but you might want to use say, 470 ohm if you want to lessen the compression effect?

Marshall uses 1K5 1K/5w as screen R's on later amps with EL34's.

[pompeiisneaks]

Cool thanks, I'll try the 1k you mentioned at first and if I think I want more, I'll try 1.5, if less compression, 470.  I'm guessing these likely need to be 3watt resistors at a minimum right?

[Willabe]

My mistake, Marshall used 1K/5w.

I'd go with the 1K/5w as Marshall knows a thing or 2 about using EL34's.     

And Doug uses that same value in his Plexi 50.

[pompeiisneaks]

Oh, don't want smoking resistors, sounds good. 

~Phil

[pompeiisneaks]

Well all the parts are on order for this build, I'll post some pics as it progresses.  I may even give a try at filming some  of it.