Improving the CX301a DHT pre-amp

An idea discussed with Rod Coleman, Andy Evans and others in DYIAudio forum which still is evolving. The purpose is to increase the output driving capability of this preamp using a cathode-follower stage. A bonus is to provide the filament bias using the cathode-follower valve filaments:

CX301a DHT preamp cathode follower

Author: Ale Moglia

"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp)

3 thoughts on “Improving the CX301a DHT pre-amp”

  1. Lookin good!
    I’m using the heaters of a 6c45pi and 6e5p in the phono section of my preamp for the 12v bias on the 4p1l line stage.
    I think lots of advantages, the heat produced is used and the idh tubes get a great supply with the coleman boards. and saved me another power supply (20v 440ma series chain with 45pi and pc86 on previous incarnation)

    1. Hi Enzo,
      Yes, absolutely. A great idea to implement. I’m limited here given the CX301a heaters are 350mA. I could add a resistor in parallel and use higher filament current and open the possibility to use a 6c45pi, 6e5P, 6n6, etc. I could do that in the future…
      Ale

  2. or use 300ma series tubes like morgan jones did and shunt them to 350ma, i,m using 39r to shunt the 6c45pi to 600ma, i think the pc86 had 27r to shunt up to the 6c45’s 440ma so many variations to try!
    enzo

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