D' Lite Tweaked Version with PI Trimmer Mod

[Structo]

I made this the other day to help a member here
and thought it may benefit others.

Tom

[dcribbs1412]

Thanks Tom

[jerrydyer]

whats the scoop on the PI trimmer. I have a general idea of what it is but in a practical sense, do you turn on the amp, put it on a scope (sine wave) and adjust to sight or sound? thanx

[Structo]

Well I don't have a scope.
Many here do not.

I was told to turn the amp up quite loud on the clean channel and lightly brush the strings. I was told a single coil neck pickup would work the best.
As you are brushing the strings lightly you are listening for an increase in overtones and bloom, that feels like it's about to feedback.
When you turn the trimmer pot you want to do very small adjustments then brush the strings a few times.

There is a bit of a lag for the adjustment to be heard probably because of the coupling caps.
This was what I missed the first time I tried it. I expected immediate returns on the adjustment.
But no, you have to give it time for the adjustment to be heard.

So brush the strings, listen, turn the trimmer a tiny bit, brush the strings, listen.
Repeat until you get the best bloom into harmonics and good overtones.

Once you find the right spot it will be apparent.
You can also measure the plate voltage on the PI resistors.
The voltage on pin 1 will be around 5-6v higher than pin 6 when adjusted properly.

If you can't get it to do what I said, try another 12ax7. Tubes can vary wildly from each other. Even the same brand and lot number will vary in plate voltage and current draw.

Hope this helps.

[ampedup]

Is this schematic good for the 6v6 dlite or just for the 6l6 version?

[Structo]

The original layout for the D'lite is designed for 6V6.

This is tweaked more towards using 6L6 tubes.

[Dr d]

Hi Tom, this is a very worthwhile mod and am surprised it was left out in the first place. Just a word of caution....when adjusting the trim pot, bear in mind you are close to some pretty high voltages. Only the other day I got a bolt from 300v doing this very adjustment!!!!!

[Structo]

Yep, you have to be careful.

They do make plastic shaft screw drivers for adjusting tuners and such.

I'll bet that was a real wake up call!