Bassman 100 Recommendations

[sjwood3]

Hi All,
   I have a 1975 Bassman 100 (Non UL) that has been modded prior to my possession.  The master was converted to a supposed 'Presence' knob, but all it did was add a nasty noise when turned up.  Based on my comparison to the schematic I've included below, I think the previous owner was attempting to do some mods I have no interest in further pursuing.   Ive replaced the power filter caps, brought them up on a variac, removed the death cap, bypassed the ground switch, replaced the phase inverter 0.1 caps.  The bias range resistor was a 270 ohm, I put a 470 back in there.  The bias supply looks like it does in a Fender Twin reverb, instead of what you see in the original schematic.   Looks like an 82K and 100K resister were added in the PI area as well.  The 2000pF x2 off the power tubes was removed as well as the caps from the treble to volume pots on both channels.  A .01 cap in series with a 22k resitor was removed near the 100 ohm to ground.  The LTP is where it really got interesting.   I'm assuming the presence mod that was attempted before had some effect on the values that were used in the LTP and the NFB loop.   I'd like to incorporate a 1M/470ohm/1M LTP similar to the ab 763 style.    I think those are all the changes I noticed.   

Here's my goal, I want to add a PPIMV (I'm fully capable of doing that, no help needed).   I want to know the best way to marry the preamp section and the PI together without the presence or the original master volume.  Then I will add the PPIMV afterwards.  Multiple options?  I have a vague idea, not an amp designer.  I just want to get this thing kickin again.  Any help or advice appreciated. 

https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Bassman-100-Schematic.pdf

Attached  pics of the original state.....

[DummyLoad]

I want to know the best way to marry the preamp section and the PI together without the presence or the original master volume.

see attached.

--pete

[Latole]

Master volume circuit I use few times;
Keep the Bassman 100,  0.1 uf 600 volts and replace 100nf ( mv schematic)with 0.1 mfd .

[Willabe]

Master volume circuit I use few times;Keep the Bassman 100,  0.1 uf 600 volts and replace 100nf ( mv schematic)with 0.1 mfd.

MV goes AFTER the PI plate R's and the .1 coupling cap.

That's why they have a coupling cap after AND before the MV.

This drawing you posted is wrong.

[Latole]

So why my amps's Master volumes work so fine ? 

[Willabe]

So why my amps's Master volumes work so fine ?

Because it's not wired like your drawing.

If you have a coupling cap between the PI plates and the plate R's how does the dcv get to the PI tubes plates?   

The MV you posted has to go AFTER the plate R's.

[sluckey]

Finish ;

Never seen this before.   

[sluckey]

We have always something to learn !

Teach me. Why four pots? I'm also curious about the 47K pots. I didn't expect to see them. Especially with the junction of the pots connected to nothing else.

[Latole]

Finish ;

Never seen this before.   

Sorry it's a mistake in my drawing 

Removed

[Latole]

that's the one ;

[sluckey]

that's the one ;

Once again. Teach me. What's the purpose of the two 47K resistors? And how do you get bias voltage to the grids?

[Latole]

How ? Easy mods :

[sjwood3]

see attached.

--pete
[/quote]

Ah, thank you.  Worked perfectly.  My current limiter was lighting up immediately, the .1/200v Ac shunt had given up.  Replaced it and all is good.  I'm interested in the MV discussion as well. 

[PRR]

How ? Easy mods :

[2deaf]

Wite-out day

[AmberB]

Is the PPI master volume better than the standard one, or just different?

[sluckey]

Wite-out day

Of course. I was just nitpicking Latole's drawings.   

[Willabe]

Is the PPI master volume better than the standard one, or just different?

They sound different.