Schematic of Paul C Mod Question

[Ed_Chambley]

In this comparison schematic, what would be the difference instead of adding the 2m2 resistor from removing the 1meg and adding 3m3 resistor.

[sluckey]

In this comparison schematic, what would be the difference instead of adding the 2m2 resistor from removing the 1meg and adding 3m3 resistor.

I'm not quite sure what you are asking. The original circuit is bootstrap biased. Paul C is fixed bias. A pic of what you ask would probably help.

[Ed_Chambley]

Sorry, this should clear it up.

[SILVERGUN]

Look at those 2 resistors as being in parallel and you'll come up with a combined value of about 680K.

It might have just been easier for him to leave the 1M there and add the 2.2M 
Or he just didn't have any 680Ks in stock.....I don't.   

[Ed_Chambley]

Look at those 2 resistors as being in parallel and you'll come up with a combined value of about 680K.

It might have just been easier for him to leave the 1M there and add the 2.2M 
Or he just didn't have any 680Ks in stock.....I don't.   

Yes, I see it is 687.5k.  The value is not what I was thinking, I was wondering if there is a specific reason for having the parallel.  Since I use a 4m7 instead of the 2m2 in princetons that is 825k.

I tried a single 1 meg linear pot last night in place of both resistors and the results were like a master, but I do not know if this would cause a problem.

I have been messing around with split load a lot lately and am really liking the results.

[sluckey]

Look at those 2 resistors as being in parallel and you'll come up with a combined value of about 680K.

No no no. The resistors are not in parallel. The bottom end of the 2.2M connects to B+. This creates a voltage divider between B+ and ground that places a large positive voltage on the grid of the tube. IOW fixed bias.

Sorry, this should clear it up.

You cannot remove the 1M. Doing so will break the fixed bias voltage divider and put full B+ on the grid!

 

[Ed_Chambley]

The bottom end of the 2.2M connects to B+. This creates a voltage divider between B+ and ground that places a large positive voltage on the grid of the tube. IOW fixed bias.


[/quote]
Would it create a problem to use a pot instead of the 2m2 resistor?  I am attempting to find an alternative place for a MV, but since I have never seen this done it probably will not work.

[SILVERGUN]

WOW!
Sorry guys....that's what I get for posting pre-coffee... 
I was looking at the 2.2M as going to ground....(just used to seeing schematics that way,,,so the snippet got me)

 

[Ed_Chambley]

WOW!
Sorry guys....that's what I get for posting pre-coffee... 
I was looking at the 2.2M as going to ground....(just used to seeing schematics that way,,,so the snippet got me)

 

No biggie, I have done this mod at least 50 times and I know they are not in parallel.  What I was getting at is I put a pot on last night in-place of the 4m7 I have in a build and it sounded great as a Master Volume.  I am just wanting to know what I am going to fry as my ideas usually come with drawbacks.

[sluckey]

Would it create a problem to use a pot instead of the 2m2 resistor?  I am attempting to find an alternative place for a MV, but since I have never seen this done it probably will not work.

Yes. You will also be messing with the fixed bias on the tube.

If you want to use a pre PI MV and the Paul C mod, I suggest you simply put a cap and standard wired volume control BEFORE that .02 coupling cap.

If you want to add a pre PI MV to the original you can use this circuit. (Sure seems like this discussion was just on the forum in the past few weeks. Not sure, though.)

[Ed_Chambley]

Would it create a problem to use a pot instead of the 2m2 resistor?  I am attempting to find an alternative place for a MV, but since I have never seen this done it probably will not work.

Yes. You will also be messing with the fixed bias on the tube.

If you want to use a pre PI MV and the Paul C mod, I suggest you simply put a cap and standard wired volume control BEFORE that .02 coupling cap.

If you want to add a pre PI MV to the original you can use this circuit. (Sure seems like this discussion was just on the forum in the past few weeks. Not sure, though.)

It was discussed recently, that is why I am messing with it.  The amp is not a 5E3, but does have a split load in the same configuration as an AA1164, but with a PT and OT designed for a 50 watt Bassman.  

The cap and volume sounds like the deal. I actually wired up a Dual pot master but it does not sound good at all.

I sort of stole the preamp from a plexi and the power section is a beefed up Princeton.  Kinda cool sounding and is running KT66's.

Thanks for the input, I will give it a try tonight.