For anyone wanting to set their amps PI Trimmer

[boldaslove6789]

Thought I'd post my method for setting the PI trimmer.

(Note, a 12ax7 with matched triode's works best for the PI)

Please be safe when doing this, there is dangerous Lethal Voltages inside a tube amp. Only do this unless you have knowlegde of how tube amps work and the methods of being safe when inside an amp when its ON.

Thanx and be Safe!

Here ya go:

You'll need at least a digital Multimeter to measure Volts .

Here's my tried and true method for setting the PI trimmer for Max Harmonic Feedback.

Set your rig up how you normally use it (effects in loop etc.)

Make sure the amp is hooked up to a Load (your Speaker cab), and the Ohm setting is right for the speakers you're using.

Turn the amp ON, Standby ON.

Put the Black Multimeter probe (ground) into the Black Banana Bias Test socket under the chassis, or if you don't have a Bias test socket, use an Alligator clip and clip it right on the Chassis so that the Multimeter is grounded properly.

Set your Meter to volts.

Use the Following settings on your amp:

Preamp Vol: 12:00
Overdrive Level (Gain): 11:00
Overdrive Master Vol (or Ratio): 12:00
Clean Master Vol: 11:00
Presence: 12:00

If you're using a Dumbleator:

Send:12:00
Return: 12:00
(Bright switches Off)

Turn the amps Preamp Boost ON, and the Overdrive ON.

The amp should be quite loud.

There should be 6 trim pots total inside your amp if it is HRM, and 3 if its a NON-HRM. The PI trimmer is the trim pot that is in the center of the amp, on the preamp board, towards the end of the board closest to the Power amps Filter caps.

Using the RED Multimeter Probe, Measure each leg of the trim pot. (the side of the trim pot with the 2 legs pointing towards the back of the amp)

Set the trimmer so that there is 7v (volts) difference on each side. The Rightmost leg (towards the Pwr amp) should have more voltage of the two.

The amp should be quite loud.

Then use a Les Paul or Tele on the bridge Pickup setting and hold single notes that normally feedback. Face the guitars pickup to the speaker cab.

Adjust the trimmer till you get the maximum Harmonic Feedback on single notes & Pwr chords.

Take a Marker and mark the setting you like the best.

[amplifiednation]

Greg,
I wanted to say thanks...this looks really cool. When I'm done with cab work today I'm going to be sure to give this a whirl if i have time to take the amp out for the wife gets back from work!!

[martin manning]

PSA- Don't know why this is posted twice... see the "sticky" in the Dumble Discussion section which includes discussion and several other methods for setting this trimmer.