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Thursday, February 20, 2014

211 Drives 211, Part 4

Hi!

First sounds from one channel of the 211/211 amplifier!




After the first amplifier section was finished, I did the assembly of it's power supply unit which is built in the same circular style, with several round plates carrying submodules. Starting from the bottom, the first one holds the main power transformer for the high voltage and the connectors for umbilicals and mains, which plug in from the bottom:




A set of bleeder resistors is mounted on the same sub assembly:




The next level holds the filament transformers and chokes:





The rectifier bridges for the filament voltages are mounted on solder terminals in the middle, stacked on top of each other:




Then the smoothing caps for the filaments:




The two resistors on top of the stack are bleeder resistors to ensure the filament chokes will carry critical current for proper choke input operation even when the amplifier is disconnected from the PSU.





Chokes and large paper in oil caps for the smoothing of the high voltage supplies for output tube and driver:




And finally the top plate which holds the sockets for the rectifier tubes:





Rectification is done with a full wave bridge which can either consist of a pair of mercury vapour 866A, supplemented by a pair of 6CG3 TV dampers, or alternatively a bridge of 4 6CG3s.




The completed power supply:





View from the top:





The blue glow of the mercury rectifiers:





First test of the amp with the PSU, here with 836 instead of 866As:




The capacitors lying on top of the amp is a last minute tweak. The amp is playing nicely, tweaking is finished and the assembly of the second channel can start. Different versions for the housing are also in preparation. Stay tuned!

Best regards

Thomas




11 comments:

  1. Hi Thomas,

    this is very inspiring stuff! So to say a "Tower of Power". I'm really curious about what enclosures you come up with.

    Regards, Jonathan

    ReplyDelete
  2. Do you consider mercury rectifiers to be absolutely safe to use in normal (wife, children, pets) conditions?

    ReplyDelete
    Replies
    1. Hi!
      Don't use MV rectifiers with children around. They need utmost precaution. That's why I have set this PSU up such that it can alternatively use 4 6CG3

      Thomas

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    2. Hi!
      What is the tweak cap (40uF ?) from filament to PE for?

      Best,
      Daniel

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    3. Hi Daniel,

      sorry no circuit details will be shared on this amp which is the most elaborate power amp I have built so far...

      Thomas

      Delete
  3. Thanks for clarification re MV rectifiers. Though they are hard to resist as they sound better than any other rectifier tube. What about xenon rectifiers? Do you recommend similar precautions for xenon rectifiers that can be used as a replacement for 866A like 3B28 and what are your thoughts in general re xenon rectifiers soundwise.

    ReplyDelete
    Replies
    1. Hi!
      With kids around, rectifiers with plate connectors on the top are generally not safe IMHO. Unless they are not accessible. I would go for an all vacuum tube solution with TV dampers for example.

      Or if you only want to avoid the mercury hazard, use the 836

      Best regards

      Thomas

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  4. Are there any TV dampers of your preference that are drop in replacement for 866a and similar 4-pin rectifiers?

    ReplyDelete
    Replies
    1. Hi!
      No TV damper is a drop in replacement. A 6CG3 fits well but needs different heater voltage. As mentioned the 836 is pretty much a drop in replacement

      Thomas

      Delete
  5. La réalisation est très originale. Au final, cet ampli est très agréable à regarder.
    Félicitations!

    Jean-Pierre Broillet

    ReplyDelete