Tube Amplifier 6L6

This is a modified Elekit TU-8200, which is sold as kit or in build version by THL-Audio, Taipei. The modification has been reviewed by the original Japanese designer of the amplifier and received a high appreciation for the good design and innovative configuration. VDP-Audio saw an excellent chance to lift the standard quality to a higher class, for a modest price. What did we do ?

  • Although very commonly applied, also in high-end amplifiers, we find the 12AU7 sounding somewhat dull , and it is often not well capable to drive the power-tubes. We use NOS 6n6p tubes, which are rarely applied, but in fact combine good performance with a great musical quality. The 6n6p tube is a different type than the 12AU7, and therefore we rewired the tube sockets to the PCB.
  • We power the 6n6p tubes in the anode circuit with a cascade type Constant Current Supply, using 10M45 mosfets. This brings 3 great advantages:
    1. It gives a lower load to the 6n6p tube which results in a very good linearity.
    2. There is a lower output impedance and by that a lower Miller effect in the power-tubes. This is an excellent way to drive the power-tubes !
    3. And last but not least, it improves the PSRR significantly, which results in much less distortion and better sound quality.
  • We took out the overall feedback system. Overall feedback makes an amplifier sound dull.
  • We added local feedback on the power-tube 6L6GC.
  • We took out the switching possibility for triode/ ultra linear/ pentode mode, and fixed it to pentode mode. This gives the maximal power output for this amplifier. With our modification, the pentode tubes behaves like a linear triode because of the local feedback. This type of set-up is called super triode connection amplification. This combines the higher pentode output power capacity with the more musical ability of a triode.
  • In this innovative configuration, we found that the original Electro Harmonix 6L6 tubes can outcompete other possible tubes like the KT88, in this amplifier. The combination 6n6p + 6L6 is fixed. Tube rolling with other types is not advised because the voltages and currents will not match or not be sufficient. The EH 6L6GC is in the top of new 6L6 tubes. Of course, with NOS tubes like the Sylvania or even the Philips 6L6, the amplifier will give an even more refined sound. Output power : 2x 6,5W
  • We upgraded the coupling capacitors, but we don’t see this as a tuning matter; we don’t apply typical ‘audiophile’ (expensive) capacitors. Those often come with certain sound characters and colorization. To us, the components in this function need to be neutral, and we have spent many time and effort to source for this quality. We have a rather unique process of defining the sound quality or grade of neutrality when comparing capacitors.
The result ? A truly wonderful and amazingly musical amplifier for its price, that can outcompete many in a much higher price segment.