F5 power amplifier

[Beftus]

Originally Posted by Russellc

How is this done in circuit? (I've already soldered them in place.)

Russellc

Measure resistance between the right and left leg (ignore middle leg) with a DMM. See how resistance changes when you rotate the screw.

[rikkert1978]

Originally Posted by westend

This was my understanding, also, regarding the trim pots, until I fired the amp for the first time. I am using C Villers boards and the Bourns 5K trimpots. If the trimmers are turned counter-clockwise, full current will be delivered to the circuit. The trimmers must be turned clockwise to zero the current You can read the gory details Here. Fortunately, my components survived this misstep and the amp is settling in well.

I have measured the bourn pots and as used with cvillers boards, I get 5k (maxed out) between pin 1 and 2. Thats turned CLOCKWISE btw.
Now I am doubting which is the correct way to turn em. Any thoughts?

Not that I doubt your experience Westend, but just wanne make sure that I install these correctly.

[tinitus]

From Cviller board

[Zen Mod]

trimpots in F5 are used as adjustable resistors - that's acomplished tying middle pin with one of outer pins ; so - that's two pole thingy

it doesnt matter with left or right one .... actual positioning in physical domain will give you decrease of resistance clockwise or anticlockwise .

for proper adjusting - one need to use brain , instead of putting parts as pieces of puzzle .

use that DMM ; prior powering up that amp , be sure that trimpots soldered in circuit are adjusted to short between pins

[juma]

Originally Posted by Zen Mod

...one need to use brain...

You are doing it again - stop asking too much !

Originally Posted by Zen Mod

.... be sure that trimpots soldered in circuit are adjusted to short between pins

Short is just another word for "opposite of long" - you mean it should read 0 Ohms on multimeter ? Why don't you say so?

[rikkert1978]

Originally Posted by Zen Mod

trimpots in F5 are used as adjustable resistors - that's acomplished tying middle pin with one of outer pins ; so - that's two pole thingy

it doesnt matter with left or right one .... actual positioning in physical domain will give you decrease of resistance clockwise or anticlockwise .

for proper adjusting - one need to use brain , instead of putting parts as pieces of puzzle .

use that DMM ; prior powering up that amp , be sure that trimpots soldered in circuit are adjusted to short between pins

Thanks, I have it figured out now.
I understand that its the physical way they are installed that dictates which way to turn. I just was not sure what was the right value (0, or 5k)

When installing them on cvillers board with pin 1 and 2 shorted, its clockwise to get to 0 ohm.

If you mount the pots the other way (pin 3,2 shorted) it must be turned counterclockwise to get 0 ohm.

I should get some sleep

[Zen Mod]

Originally Posted by juma

You are doing it again - stop asking too much !


Short is just another word for "opposite of long" - you mean it should read 0 Ohms on multimeter ? Why don't you say so?

yeah .... I'll answer that to your alter ego ......

remember that TO3 cans are still in my possession .....

[juma]

Originally Posted by Zen Mod

yeah .... TO3 cans are still in my possession .....

You got me there!

[Zen Mod]

Originally Posted by rikkert1978

.....

I should get some sleep

sleep well

[audiorasp]

Russelc, clip your ohm meter across R3 and turn the pot screw and see which way the resistance goes. Keep turning the screw toward the direction that lowers the resistance until the resistance quits dropping. Do the same with the meter across R4. This will be your setting for the initial power up.

George