PI Trimmer

[Sonic]

Silly question, but I want to add a trimmer/balance to my PI. Where do you guys buy those mini potentiometers, and what value and rating do you recommend? Thanks for any advice!

[Structo]

I like these Piher trimmers.

I prefer the horizontal mount/ vertical adjust because I have slipped off of a vertical mount one before and got shocked.
In other words, I like the screw driver to be vertical into the trimmer.

(best to use non conductive screw driver as well....)

http://www.mouser.com/ProductDetail/Pih ... FOmbu/U%3d

This is a 10K, supposedly if you use a larger value it gives a bit more headroom. I haven't experimented with it enough to know.

Dumble used the vertical mount/ horizontal adjust if you want to be true to the design.

[Sonic]

Perfect! Thank you Tom!!

[martin manning]

I prefer the horizontal mount/ vertical adjust because I have slipped off of a vertical mount one before and got shocked.
In other words, I like the screw driver to be vertical into the trimmer.

This job needs a non-metallic tool. I like to use a 12" bamboo skewer with the end whittled into a flat blade. The extra length means you can get the angle you need to adjust a vertical trimmer with your hand outside the chassis.

[dobbhill]

A 10-turn trimmer makes it easier....

[Sonic]

Thanks to all. Tom, is 1/3 watt a high enough rating for the PI. This is what I was unsure about.

[David Root]

Martin, that is a good idea on the trimmer adjusting tool. Cheap too! I have been trying to use a wood spudger with flathead crewdriver shaped tip but it's too wide, I guess I should narrow it a bit.

[Structo]

Thanks to all. Tom, is 1/3 watt a high enough rating for the PI. This is what I was unsure about.

Yeah, there is very little current on that trimmer, so it is safe.

[Mark]

This one of those crazy questions. Sonically, (okay a little pun intended) what does the 10K do?

Does it effect the tone of the amp, or is it done to get maximum headroom from the amp?

[martin manning]

This one of those crazy questions. Sonically, (okay a little pun intended) what does the 10K do? Does it effect the tone of the amp, or is it done to get maximum headroom from the amp?

It's a tone thing. With equal plate loads the LTP phase inverter doesn't have balanced (equal amplitude) outputs from the inverting and non-inverting sides, and so ultimately the distortion and harmonics of the speaker output are affected. Using fixed plate resistors that are miss-matched (82k on the inverting and 100k on the non-inverting triode, e.g.) is a common solution; adding the trimmer provides a way to fine-tune the result.

[Sonic]

Always great info here. Thanks to everyone!

[Mark]

Thanks for the reply, much appreciated.

Dare I ask how most people adjust this pot, is the effect subtle or easily heard?

[martin manning]

Dare I ask how most people adjust this pot, is the effect subtle or easily heard?

Do a search. It's kind of subtle, and there is more than one way to go about it. Here's a start:
https://tubeamparchive.com/viewtopic.ph ... g++trimmer

[Mark]

Thanks Martin. Interesting reading.