To keep hum at a minimum, the filaments are heated using DC. The power supply is external to the preamp section and consists of a RCA-83 mercury rectifier and two 50H chokes.
For more project details including schematics and an enclosure construction guide, see: DIY 5687 LED Biased Tube Preamplifier.
Related Tube Preamplifier Projects:
- Mark's build of the DIY 12AX7 Tube Preamplifier Kit
- Bruce's build of the DIY 12AX7 Tube Preamp Kit
- Alan's simple DIY 12AX7 / 12AU7 Tube Preamplifier
What's Playing: Fleetwood Mac - Landslide