cave dweller and the 50k trimpot...

[greysun]

I've decided to figure out how to use up all my excess parts collecting dust. I'll build up some stuff I didn't think I wanted, but hear good things about... up first: CAVEDWELLER!

I have everything but the 50k trimpot. I have a 20k trimpot, a few 10k trimpots, and a 2m trimpot.

I know you can extend a pots value, but that seems iffy to me since this is to get the voltages right into the pt2399.

Thoughts on a remedy?

one thought I had: I have all kinds of resistor values, and could just socket the trimpot and see which resistor works best, but that might be excessive.

any thoughts or guidance here? Hoping I can make it work... :-)

as always: thank you in advance!

[madbean]

20k might be enough, or it might not. What I would do is leave the trimmer empty, then simply try a few resistors in there to see what gets you the closest match for biasing then use a fixed resistor. The trick is you don't have to use a socket or solder them in when testing. Just make sure both leads are contacting the pads while you measure the resulting voltage on the drain.

[somnif]

I know you can extend a pots value, but that seems iffy to me since this is to get the voltages right into the pt2399.

Just a clarification, the trimmer is to set the bias on the input buffer (the 2399 gets its juice from the 5V regulator). You want to set it so the JFET sees 6V.

Please note I am using old memories of intro Physics to make the following statements, seek verification first:

Add power, and see what the voltage looks like on pin 3 of the trimmer pads.  Measure the current too. Then you can use Ohm's law to figure out what resistance you need so you would get 6v out pin 1.

[greysun]

20k might be enough, or it might not. What I would do is leave the trimmer empty, then simply try a few resistors in there to see what gets you the closest match for biasing then use a fixed resistor. The trick is you don't have to use a socket or solder them in when testing. Just make sure both leads are contacting the pads while you measure the resulting voltage on the drain.

hmmm... in that case, would it be easier to use a 50k normal size pot to get the voltage right, then figure out that resistance and then just get the closest match resistor-wise?