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841 (VT-51) Direct Coupled to 300B SMPS B+ » greenvalve Luddite Wander SMPS 841 DC 300B


9 responses

  1. Hello,
    Wondered if you could please supply some further information about the Luddite Wander Monoblock -:

    What is the power output?
    What is the input sensitivity?
    Where can i purchase the suitable Cisco 48v smps also the 16.5v 3A and 5v 3A?
    Where can i contact Onetics?
    Although you say these smps are regulated to +/- 1v this could be +/- 16V for the B+. Is this acceptable?

    Thank you
    Trevor (UK)

    August 15, 2012 at 12:47 pm

    • Hi Trevor,

      I use a preamp with 2V signal to drive this to about 12W before audible distortion. The 16V filament supply is an SMPS ‘brick’ and the 5V supply is a traditional linear supply using Schottky diodes and a 5V 3A Hammond transformer with 800V insulation rating. Looking at the B+ voltage referenced to ground, it never varies more than 0.5V even under full load. That is the key to the dynamic sound of this amp. Ebay always has the 48V bricks available. The Cisco SMPS were designed for VOIP and have low RF and noise.

      14144 76th Pl NE
      Bothell, WA 98011-5069
      Bud Purvine
      Phone: (425) 823-2279

      Best wishes!

      August 15, 2012 at 2:12 pm

  2. Hi,

    Thanks for reply.

    Just to double check, I’ve found cisco smps on ebay fully encapsulated model no. Cisco-PSA18U-480C 34-1977-03. Is this the correct model?

    Could a smps ‘Brick’ be used for the 5V 3A supply?



    August 17, 2012 at 6:26 am

  3. Hi greenvalve,

    While waiting for your response, I have some further questions please.

    If the ‘Cisco’ power supplies I quoted are the correct ones, will they safefly handle the B+ voltage and will any diodes be required to stop inverse voltages? I notice that the power supplies used in your projects are open framed!

    Have you constructed a ‘Luddite Wander’ proper, apart from the breadboard and if so will you be posting any images in the near future?

    Where would be the best place to purchase the 841 VT51 tubes?

    Thank you

    Trevor Whitehouse.

    August 29, 2012 at 4:56 am

  4. I do not know the answer to your questions as I have never used that particular 48V brick, but all the bricks seem to have a 250V capacitor in reference to earth, so I modified them so that those caps would not explode under the high voltage B+. The same would apply to a 5V 3A brick, as it would be held at a 432V potential. I have never put this in an enclosure, just lashed it up with clips. If I have time I will definitely make a couple nice chassis for these mono blocks. For tubes, I have had very good dealings with Brent Jessee Recording.

    August 29, 2012 at 7:19 am

    • Hi greenvalve,
      Thanks for reply.
      If i am to proceed with construction of this design, I need to sort out these SMPS power supplies. Could you give me the precise model of the ones you used together with the required modifications, and where I can purchase.

      Kind regards
      Trevor Whitehouse.

      September 1, 2012 at 1:44 pm

  5. How much would a pair of these monos cost if they were made to look like your GM70 amp? Any reason why Plitron OPTs would not be desirable?

    June 2, 2013 at 9:16 am

  6. Can someone wha has built thie 300B mono have any pics or scheatics. I eould lik to see these, it’s possinle.

    June 28, 2013 at 8:20 pm

  7. Yoon, Hyug Chul


    I just want to thank you Erick for opening this information and the circuit. This is thinking out of the box and I will definitely try this.
    I only hope I can source the same SMPS in Korea.

    You are making the DIY hobby of others happier and enjyable.

    Thank you again,

    September 14, 2015 at 5:33 am

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