The project is a single-ended medium power tube / solid state hybrid amplifier delivering something above 20W RMS and can be driven directly from a CD player. Input tube is an actively loaded 6SN7.



The power stage comprises a KT66 as a cathode follower driving a 2SC5200 BJT which is cascoded by an IXFN32N120 industrial power MosFet. The MosFet takes around 80W power loss. It is mounted on a 0.4 K/W Fischer heatsink. The output signal at the MosFet drain is fed back into the screen grid of the KT66. This makes the tetrode virtually a triode and allows independent operating voltages. The KT66 runs at 300V while the solid state cascode works at 190V. Thus an electrolyte capacitor is unavoidable in the local feedback loop. Idle current of the cascode is 460mA. Thus the primary coils of the LL 1693 (230mA) output transformer are connected in parallel reflecting 250 Ohm primary impedance.



The main parts are:Lundahl chokes, power and output transformers, Mundorf audio caps, Welter 6SN7, Tung-Sol KT66, all other components from standard electronic online stores



A decorative front cover is not yet mounted for I am still struggeling with the final design.

Comments

• Jazzman53
• 13 August 2017 at 07:34PM
• While I lack the electronics knowledge to follow your project, I love the no-frills, form follows function approach. I only wish I had your talent!

• KlausB
• 18 August 2017 at 04:42AM
• Hi Jazzman53,
  thank you for nice comment. I appreciate it.