Fender Bassman Amp in a Box

[dperry]

Hi all,

First post so please be nice! I'm building this vero



Which is a slightly modified version of this



The problem is its not passing signal to the output.  Using the trimmers, I have the both the2n5457's drains tuned to 4.5v and using my homemade audio probe I am getting signal as far as the gate on the right side JFET, but after that no signal.

I've tried a few different 2n5457 and always made sure they are tuned to the correct voltage, but i'm starting to tear my hair out!

My voltages are (using 9v source)

Q1 (left side)
D - 4.56
S - 0.57
G - minus 0.008

Q2
D - 4.84
S - 0.02
G - 0

I'm guessing its a issue with Q2?!?

 

[Frank_NH]

Try connecting the 1 lug on the 1M volume control to ground.  As with Q1, you need connect Q2's gate to ground with a large value resistor (1M in the case of Q1) in order for the FET to bias correctly.

[dperry]

Sorry if i have misunderstood, but lug 1 of the volume is already connected to ground isn't it?!?  Do i need to bias Q2 with a extra resistor to ground?

[Frank_NH]

Yes - sorry, I was looking at the schematic.  You shouldn't have to bias the FET with another 1M resistor to ground at the gate.  Check for a short in that vicinity (all Q2 connections).  Also, check the orientation of the your FET (I know I flipped them before without thinking...).