Hi guysI'm wondering if anyone could shed some light on why I can't bias my 3904 transistors....I'm using a 25kb pot and can't get the voltage below 9.0volts....I'm using a one spot for power in my test rig and when I have my dmm in the tp I'm getting 9.4volts......the hipster is supposed to be biased to around 4.5 volts correct?...and are the 2n3904Lthe same pinouts as 2n3904? On the bottom of the transistor on the face it says OGE
My voltages are q1-C-9.13
Pin B-0
Pin E-0
Q2-E-9.19
B-9.13
C-8.87
Just to clarify, is the bias trimmer changing the voltage at all?
Do you have the bias pot as an external, offboard one? Which lugs did you connect?
Post all voltages at all pins of both transistors, and pictures.
Quote from: Bret608 on December 11, 2013, 09:26:13 PM
Just to clarify, is the bias trimmer changing the voltage at all?
Do you have the bias pot as an external, offboard one? Which lugs did you connect?
The bias pot is wired off board...its changing the voltage by .5 of a volt max.....
Bump
Here are a couple of things you can try.
First, I see on the Hipster layout that pin one of the bias trim is in the center. On the offboard pot, this is wired to one of the outer lugs, right? In other words, looking at the schematic and layout, you can double check you've got the right lugs going to the right pads on the board. I can't see it in your pictures, but that is one thing to check.
Next, take your DMM and measure the resistance across lugs 1 and 3 of the bias pot at different points on the pot's rotation. Does it vary?