Kustom Lead 3 s - repair

[Mathias]

R4 measures 0.63V but is slowly dropping.

10mv DC on the output and is slowly rising.

C6 seems fine. I desoldered it and tested it measures 100pf.

*measured without load

 

[Voyager10]

OK, that seems like it might be working. The voltages will change slightly as things warm up but should stabilise after a few minutes. I'd expect Q3 to get warm, but not too hot to touch (like 70 C or more).

If the power supply caps are literally 50 years old that could certainly cause hum due to poor smoothing of the supply rails.

 

[CJ]

The light bulb is good for starting a suspect amp with no load, but if you attach a load, that light bulb might light up as the current is going in and the current is going out,

I use a light bulb for my winding machine, if you grab the chuck, the light bulb will light up and decrease power to the stopped motor, its kind of like having a clutch on the machine,,

 

[Mathias]

OK, that seems like it might be working. The voltages will change slightly as things warm up but should stabilise after a few minutes. I'd expect Q3 to get warm, but not too hot to touch (like 70 C or more).

If the power supply caps are literally 50 years old that could certainly cause hum due to poor smoothing of the supply rails.

Seems like it is fine! When turning up the volume it’s not that bad after all.

Thanks for all the help! Much appreciated

 

[Mathias]

The light bulb is good for starting a suspect amp with no load, but if you attach a load, that light bulb might light up as the current is going in and the current is going out,

I use a light bulb for my winding machine, if you grab the chuck, the light bulb will light up and decrease power to the stopped motor, its kind of like having a clutch on the machine,,

Lovely! Before I read about the Ampeg I was wondering the same, what if it's just drawing current and maxing out the bulb... and your answer gave me good fate! Much appreciated!