Will these part values be good for situation?

[Papa Jim]

Sorry, guys I can build anything but am not skilled at parts values on designs. Attached is the section of the 2W Trainwreck style amp I built, where I want to add a Master Volume (PPIMV).  I need some reccomendations on a few resistor and cap values. The values shown in blue are original schematic values, and the values and parts in green are the new PPIVM parts and values. Anways my hope is that the mod will turn out as good as the amp did. So would someone skilled in amp circuits please take a look at it. Thanks to all.

[2deaf]

Get rid of Rb, Rd, Ra, and Re and that -V Bias thing.

OT lug 2 is connected to lug 4 instead of to the 8 ohm lug on the selector switch.

NFB and presence will cease to function as you turn the PPIMV down.

[PRR]

> that -V Bias thing.

Some negative bias is needed because there is no cathode bias for the 6SN7.

So it should look a lot like a big fix-bias amp.

Hasn't that been done before?

http://www.amparchives.com/Amp%20Archives/Marshall/Schematics%20&%20Layouts/PPIMV's/Improved%20PPIMV.gif

[Papa Jim]

Whoops, my bad. I must have messed that up just in the schematic last night. The amp is not wired like that schem though. It is exactly like you said to do. Attached is the corrected schematic. Now back to the PPIVM like I need badly sorry.

[2deaf]

> that -V Bias thing.

Some negative bias is needed because there is no cathode bias for the 6SN7.

The 4-4-0 already has V-1 @ -12.5 and V-2 @ -12.3 coming off of VR1 and VR2 in the bias circuit.  That -V bias thing is carried over from the diagram you referenced and is not appropriate for this amp.

[Papa Jim]

So I should go this route with the circuit you showed us. The new PPIVM parts are surrounded in red. The other amp parts and values are stock. What ya think about this new attachment.

[2deaf]

Why did you change to a 100K linear dual-ganged pot.?

[Papa Jim]

Why did you change to a 100K linear dual-ganged pot.?

Thanks so much for catching that. Dang, I don't know where my mind has gone. Too many irons in the fire.  It is indeed a 500K. I had that drawing also that PRR posted somewhere and grabbed it. It had been changed for something else I was playing with. I changed it to 500K and attached it here.

[kagliostro]

Too many irons in the fire.

 

Franco

[tubeswell]

Suggest you try the NFB/presence control schematic from the 6G6B Bassman  as it won't have that characteristic scratchy sound that a tweed bassman presence control has.