DPDT PPIMV

[tubenit]

Just an idea I've thought of.    Haven't tried it yet.

I typically have a dual gang pot PPIMV  either set at 1:00 or totally on.  I was thinking that I could measure the values of those to ground and implement them on a simple DPDT switch.  Might be a simple way of lowering volume for playing at home?

I am NOT thinking of this as something someone would switch on the fly, but instead turning the amp off and switching it.

IF this works, it might have the slight advantage of accurate value resistors given that the PPIMV dual gang pots seldom seem to have the same resistance for each of the pots.

Think this might work?    I'm guessing if it does that some amp already uses this idea and I haven't seen it on a schematic yet.   

With respect, Tubenit

[rake]

That's actually a good idea.
Sort of a fixed value master volume?
You may have to experiment with resistor values
to achieve the right amount of cut but it sounds logical.

[2deaf]

I don't really understand how a voltage divider is getting inserted by looking at the diagram. 

[tubenit]

It's not what I would view as a voltage divider.  Simply 100k to ground ........... OR  220k to ground.

Looking at the DPDT,  the signal goes to the center row.  When the center row connects to the right row, it send 100k to ground.

When the center row connects to the left row, it puts 120k in series with 100k which means 220k to ground.

They way you have drawn yours is different then what I had in mind.  Essentially your drawings would put a 120k in series with the 10k grid resistor on the power tube.  I am not wanting to do that.

With respect, Tubenit

[sluckey]

Think this might work?

No. All you are doing is switching from a 100K grid leak to a 220K grid leak. I doubt you will even hear a change in loudness. You 'may' be able to see a slight change in signal amplitude using a scope.

To do what you propose would involve switching two resistors in each grid circuit. That's a total of four resistors for both grids. Switching will become complicated. You'll never find a switching solution that is cheaper and more elegant (or useful) than the dual gang pot.

[kagliostro]

If the concern is the fact that there is a difference (due to tollerance) between the two pot

a solution can be to parallel each pot with a trimmer of an adequate value

the final pot resistance value can be finely tune via the trimmer

Franco

[tubenit]

Glad to have the feedback and expertise here!  Thanks!  I value knowing an idea is not a good one also.

With respect, Tubenit

[2deaf]

They way you have drawn yours is different then what I had in mind.

The one with the DPDT switch is precisely what you described verbally and is consistent with the title of this thread.  The one with the DPST switch combines a voltage divider with a change in grid leak values to accommodate both the verbal description and the diagram.

A two position PPIMV that you verbally described utilizing different voltage dividers is certainly a viable idea for a "Half Power" type switch.  The diagram is not a viable idea.     

[PRR]

Agree with 2deaf and Sluckey. Your pot is a voltage divider, not just a variable resistor. Agree you want like 2deaf drew. I started re-drawing but fell asleep, found this on my screen this morning.

[tubenit]

The one with the DPDT switch is precisely what you described verbally and is consistent with the title of this thread.  The one with the DPST switch combines a voltage divider with a change in grid leak values to accommodate both the verbal description and the diagram.

A two position PPIMV that you verbally described utilizing different voltage dividers is certainly a viable idea for a "Half Power" type switch.  The diagram is not a viable idea.     

I stand corrected!  Thanks for the information.

PRR, thanks for the drawing! I appreciate it.

With respect, Tubenit

[PRR]

My diagram is the same as the lower idea in 2deaf's diagram posted before mine.

2deaf's upper drawing is different, saves a cent on the switch, but is not sure to be same-as a half-pot sound.