Posted by necplusultra (A) on February 10, 2009 at 07:12:59

Greetings,

I want to build a seth amp and yhis would be my first attempt at building from scratch. I have built BH amps before.

I have a few questions:

1) I want to build the amp with MQ Ni products. Can I replace the stock plate chokes with the fs-100 which I would obtain today? If this is possible, which other parts are necessary to replace?


2) the 47+47 capacitor is hard to find (discontinued) However, I found a jenson 47+47. Would this fit or can I replace this by two 47 uF caps?

3) I'd also like to but an attenuator for volume control. What specs do I need to put in a ladder step attenuator?


thanks and kind regards to all.

• RE: WANT TO BUILD SETH AMP - RPM33 19:04:04 02/17/09 (0)
  In Reply to: RE: WANT TO BUILD SETH AMP posted by necplusultra on February 10, 2009 at 07:12:59

  Why do you want an attenuator - no preamp? For shame. You must use grid chokes for optimum performance - they are very special. Build as specified - it is an excellent design. I built mine with pinstripe iron.
  
  

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• RE: WANT TO BUILD SETH AMP - nullspace 15:07:47 02/10/09 (0)
  In Reply to: RE: WANT TO BUILD SETH AMP posted by necplusultra on February 10, 2009 at 07:12:59

  Hi,
  
  1) Referring to the the original Seth circuit, there aren't any plate chokes specified. There are grid chokes and autoformer phase splitters, and I don't think there are any possible MQ substitutions to be made.
  
  2) The one Jensen 47uf+47uf I've seen is rated for 500Vdc, so I suspect it's fine. Of course, you could use any pair of 47uf capacitors of a sufficient voltage rating.
  
  3) I suppose you could replace the grid choke with almost any stepped attenuator, mostly depends on what the preceding stage is. You might think of using the B7 10k:10k input transformer plus a 10k attenuator since you'll be forgoing the cost of the grid chokes...
  
  Regards,
  John
  

  • SETH Circuit   (Open in New Window)

  
  

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• plate chokes? - braubeat 11:22:00 02/10/09 (2)
  In Reply to: RE: WANT TO BUILD SETH AMP posted by necplusultra on February 10, 2009 at 07:12:59

  Hello
  What version of the seth amp are you building? I was not aware that the seth used plate chokes.
  Michael
  
  

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  • RE: plate chokes? - necplusultra 12:22:23 02/10/09 (1)
    In Reply to: RE: plate chokes? posted by braubeat on February 10, 2009 at 11:22:00

    first version witth 2a3 tubes.
    
    Perhaps these plate chokes are not appropriate for this application.
    
    
    

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    • The first and 2nd version both use a grid choke - Bas Horneman 02:07:46 02/11/09 (0)
      In Reply to: RE: plate chokes? posted by necplusultra on February 10, 2009 at 12:22:23

      for phase splitting. The EXO 173 PPS was used for that. And you need to get that part if you want the SETH. The FS100 is a very different beast.
      
      Kind regards,
      Bas
      To infinity and beyond!!!
      
      

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