Tube resources

• Forum topic about AC4 build
• Doug circuits AC4 build
• Youtube - Pathfinder 10 Speaker upgrade
• Tubetown - Molly Kit
• The valve wizard - A whole lot of information!
• Tube startup procedure
• Hoffman - Grounding
• Aikenamps - Grounding
• Heater wiring
• Class B amplifiers tutorial. Good tutorial, it is however geared towards solid state amps.
• Tubes 201 - How vacuum tubes really work
• Turner audio has some nice descriptions to find out safe operation points for push-pull amplifiers.

Spice simulation:

• AmpBooks - Spice simulation
• DiyAudio - Distortion simulation
• LTSpice distortion measurements