grid leak trimpot?

[geoff 1965]

004.JPG

hello,
i've been working on the cascade mod on my lite2b "nearly there!" and if you look at the pic the little green resistor grounding with the black F&T cap is the grid leak "voltage divider"for the 220K cascade resistor.that one is 47K but i've been doing a lot of testing and there is a area between too much signal and too weak a signal of around 40K where i'm getting good signal & tone but quite a difference i.e. 47K is good but so is 76K and 33K each with a different character.
so i was thinking instead of having to settle on one value i could fit a 1/2 watt 100K trimpot between the turrets and insulate the capacitor lead which would pass underneath,this would also let me adjust the signal for high or low gain preamp tubes.
can anyone forsee any problems in doing this?

[crgfrench]

You could also set up 3 resistors with an SPDT on-off-on switch so you could select each value from the control panel.

[dogmeat]

I did something like that on a Hoffman AB763 I built a few years ag & used a Telecaster blade switch labeled Voice

[geoff 1965]

good suggestions guys,i'm limited for room as you can see,the chassis is only 12" X 8" so i'll go with a trimpot on the turret board.then rather than having 3 set values i can dial in exactly what resistance i want,i've found some bourns 1/2 watt "500V" pots which should be okay.
but coincidentely and relevant to your idea's i've just been looking at this matamp schematic with variable gain/voicing between the triodes,food for thought!

Matamp Series 2000.jpg

[colossal]

Nice looking build! Trim pot on the board is probably the best, most versatile option.

[crgfrench]

That Matamp seems to be missing a coupling cap between pins 6 & 2 of the PI.

[geoff 1965]

it's worked! i swapped the cascade resistor/capacitor around and the trim pot fits nicely between the turrets.i used a bourns carbon track 1/2 watt trimmer and i can fine tune the 470K now,you'll be suprised how much difference in tone you can get in around 40k width!

001.JPG

[morcey2]

That Matamp seems to be missing a coupling cap between pins 6 & 2 of the PI.

It's a DC-coupled cathodyne PI, no coupling cap required.

Matt