For this project the little and likeable penthode JAN6418 mini-tube. After testing several circuits this one sounded better:

Comments

• Especuloide
• 7 May 2012 at 08:10AM
• Tube Stage
  
  I used an inverter, based on CD 4049, to elevate from 9v to about 26v for tube plate current. The JAN 6148 has a low filament power consumption (1,25v / 10ma), the amplifier´s power consumption, in use, is about 35 milliamps. They are also very sensitive to vibration so rubber grommets will help to reduce it (I used 4 but more can improve the vibration sensibility).
  
  Transistor Stage
  
  I tested a very simple circuit, using a fair common 2N3904 that I´ve found on the internet and It fitted very well.
  
  For power supply I used an old power adapter from an electric shaver (It was small enough to be fitted in the metallic case), I only add a 2200 µF for filtering. But any low noise and regulated 9v PSU will do as well.
  
  I have tested the amplifier with the Audiotecnica Ath-M40, Shure SRH 440 and AKG 240S, it sounded very well. It can run for hours without any heat noticeable. If the volume is too high, especially when using low impedance headphones, just step up the R19 and R20 (33KΩ).
  

• Especuloide
• 7 May 2012 at 08:11AM
• Components
  
  C1, C2, C3, C4, C5, C6: 33µF – 50v, electrolytic
  C7, C10: 470nF – 100v, polyester
  C6: 220pF – 50v, ceramic
  C8, C9, C10, C11, C16: 100nF – 100v, polyester
  C12: 10µF – 10v, electrolytic
  C13, C14: 1500µF – 10v, electrolytic
  C15: 330µF – 25v, electrolytic
  D1, D2, D3, D4, D5: 1N4148
  IC1: CD 4049
  Q1, Q2, Q3, Q4: 2N3904
  R1, R2: 33KΩ – 1/8W
  R3, R6: 100KΩ – 1/8W
  R4, R7: 270KΩ – 1/8W
  R5, R8: 1MΩ – 1/8w
  R9: 680Ω – 1/8w
  R10: 33Ω – 1w
  R11, R17: 10KΩ – 1/8W
  R12, R16: 330KΩ – 1/8W
  R13, R15: 1KΩ – 1/8W
  R14, R18: 360Ω – 1/8w
  R19, R20: 33KΩ – 1/8w
  RV1: 50KΩ – potentiometer
  V1, V2: JAN6418 tube
  4 (or six) rubber grommets
  

• Especuloide
• 18 May 2013 at 09:44AM
• Changed C13 and C14 for 100uF Nichicon Muse FG.

• brian
• 23 December 2013 at 05:41AM
• Hi Especuloide i had tried your design and found out that the amp only mono instead of stereo. Both Pentode filament is connect in series. What's wrong?

• Especuloide
• 6 February 2014 at 04:47AM
• I am very sorry Brian, but I only saw your message today. The filaments are connected in series, and I had the same problem of yours because I connected the R8 to the ground instead of connecting in between the filaments. You can also feed the tubes independently (in this case R8 is connected to the ground), but be sure that they are feed with 1,25 volts. If you still have any problems send me an email : roberval.to@gmail.com