[sdiy] Hollow low-pressure ladder filter

[eric b]

>12U7s were designed for car radios, 12 volt plate supply, 30 volts maximum.

Getting hard to find---most such low-voltage devices 
are being used up rapidly by the obsessive owners 
of 1950s cars. 12K5 output tetrodes are especially scarce.

Use 6GM8s. Still being made in China, and currently
used by at least 2 makers of new tube auto hi-fi
amplifiers.

Eric Barbour
Svetlana Electron Devices
Portola Valley CA USA