Power supply for two Mullard 5-10 amps

[Dandy]

Thank you Roger. I upped the cap to 100uF. It seemed to help a bit. There was intermittent stability, especially with the lamp limiter in circuit dropping the mains voltage. Because of the chassis layout, and some loud intermittent popping that suggests to me bad joints or tube socket connections, I'm going for a rebuild.

 

[RogerMod]

Thank you Roger. I upped the cap to 100uF. It seemed to help a bit. There was intermittent stability, especially with the lamp limiter in circuit dropping the mains voltage. Because of the chassis layout, and some loud intermittent popping that suggests to me bad joints or tube socket connections, I'm going for a rebuild.

The lamp limiter in the mains may exacerbate the problem. Motorboating comes from loosness in a supply and the lamp increases the loosness. Motorboating happens when the output stage is able to drop the B+ enough to have that drop proceed though the power supply to the earlier stages. Tube rectifiers dont help this. Though you should not have to do this, a separate rectifier or supply for the front end may show this.

Recently I increased the coupling caps of a similar amp to 1 uf to cure some LF wandering with no load. That fixed it.

Keep in mind that the inductance of the OPT forms a LF pole in the output stage. If the inductance is low the pole is up in the audio region. In that case the power supply is not the problem.