• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Too much distortion


2008-02-08 11:06 am
I finished construction of a clone of AB763 circuit fender and I the following problem: when I play a E bass string (and only with this string) I have too much distortion.
This is the sample:


The amplifier is extremely quiet with no noise or hum.
The problem seems to reduce slightly using the low input.
Nell'ampli I teke off the first channel and the tremolo.

There may be a problem on the filters capacitors after the choke?


I change the value of res. on the cathode of the first and second stage of amplification from 1k5/820 to 2k7 for both (I also change caps with 0.68 uF value?), that is raising tension on the cathode to 3.8 V and doing less current flow (about 0.5 mA of 1.8 mA instead).