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About This Part of Me

About This Part Of Me

I have always been interested in steam trains and vacuum tubes. I love historical technology. Apart from that I love the ocean and hiking in the mountains, music and reading. The other major part of me is connected to people and making a difference with people. My life used to occur to me as miserable and I actually did experience a major epiphany; I now see all that seemed so miserable as the gifts that caused me to wake up and hear my soul, and what I heard is how much I love people and I got the immense privilege of letting go of the cynicism and resignation I had about myself and all people that was crushing my experience of life. The epiphany came about shortly after ceasing work due to a full-on physical and mental breakdown. It is true that while seemingly horrible things happen, looking back there is usually a great lesson and some of us are fortunate enough to wake up and see that clearly. I now would not have have my life be any different, it was and is, perfect.

Since my professional life (as a mechanical engineer) ended, I have been expressing my interest in vacuum tubes  by designing and building  vacuum tube audio audio equipment (www.triodeguy.com). This blog is intended to share what I have done as a contribution to the DIY audio community.

8 Comments
  1. Bruce Anderson permalink

    Richard
    I have a question that came to mind while thinking about figure 10: Cascode/Pentode With CCR and “Tunable” Load. Instead of the schematic you illustrate with lets say you have a phono stage with two single triode resistor loaded gain stages with RIAA in between. I understand that the initial plate resistor value effects the required RIAA components. For the sake of argument lets say we want to have the improvement provided by a CCR without needing to revise the RIAA components. Could we just add a CCR in parallel with the plate resistor? As long as that plate resistor value is high enough to not supply significant voltage (something like 100K for instance) and the CCR supplies the same voltage that the resistor did, wouldn’t the RIAA components “see” the same resistance and therefore work just the same? The CCR near infinite resistance in parallel with the 100K resistor would still be 100K to the RIAA components wouldn’t they?
    Thanks for the think piece.
    Bruce

    • Hi Bruce.
      Yes, the plate load is part of the Thevenin source resistance for the RIAA in the circuit that you have described. I think that what you suggest would work and you most likely could dial in the RIAA this way, provided that the RIAA is implemented correctly.
      Richard

    • BTW: I have described many phono-stage designs at http://www.triodeguy.com
      Richard

  2. Richard,

    Great summary of the utility of CCRs in the bigger picture that includes power supplies in the tube audio equation!

    Thanks,

    Kevin

  3. Ken Jung permalink

    I tried a cathode coupled phase inverter for my PP amplifier, which is very similar to your 6AS7PP in its output stage, employing CCR in their cathodes. I used a cascoded CCR using two DN2540 in the cathode coupled inverter, which is basically the same circuit with your 6922 stage in 6AS7 PP amplifier. I checked phase inverter output with square wave input. Even at 10KHz square wave, the output waveform exhibit some ringing, indicating that the bandwidth is somewhat limited. I tried with 10M45S/LM317 described in Walt Jung’s paper with worse results. Do you have any suggestion for this problem? You indicated that you have obtained 20KHz square wave with sharp corner in your 6AS7PP amplifier. I am not sure why I have problem with this simple circuit involving only one 6DJ8 tube. I hope you could help me on this. Thanks!

    • This is in response to your query about the use of a CCR in the tail of a differential amplifier or long-tailed-pair. (Technically, it is not a phase inverter since it has both in-phase and out-of-phase output terminals, not just one inverted phase output terminal. I know many authors use the language phase inverter however, such a description does not support understanding of the circuit. That is why the inventor, Alan Blumlein, called this circuit a long-tailed-pair, it is the long tail that allows for balanced differential action.)

      I have to say that I have never experienced the problem you have encountered. Ringing is not necessarily due to bandwidth limitation, it is due to resonance; resonance can occur due a bandwidth limitation if the circuit is close to HF oscillation; this is because as the frequency approaches the HF pole, the output phase starts to lag; if the lag causes the output phase to approach the input phase, positive feedback can occur if the (parasitically) closed loop gain exceeds unity. This is why cathode followers are prone to oscillation; the feedback is almost 100% and the output terminal is in-phase, it is an oscillator waiting to happen if the wiring is sloppy or the grid stopper is too small (or both).

      Since you already do have an in-phase output terminal, it could simply be due to the in-phase plate parasitically coupling back to the input terminal causing oscillation. What value of grid stoppers are you using?

      Another problem is that the cascode can oscillate, usually at at least 1MHz. The solution here is to use larger gate stoppers than 100R. I just hold the (X10 to minimise capacitance) probe of my scope (set at high sensitivity, say 5mV/cm) almost touching the mosfets to look for this rather than connecting it which can stop the oscillation.

      Are you testing the diff pair alone or with an output stage connected? If so if you are driving close to the limit of the output stage and it is the output transformer that is ringing, the ringing can be reflected back to the diff pair plates.

      I hope this provides you with more places to look.

  4. When someone writes an article he/she keeps the plan of a user in his/her mind that how a user can understand it.
    So that’s why this article is outstdanding. Thanks!

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