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• I think you're on the right path - KurtP 17:05:05 02/25/07 (2)
  In Reply to: Thanks, Kurt. Do you have any input on the sequence of heater wiring? (nt) posted by LowRedMoon on February 25, 2007 at 09:35:53:

  One could write an entire chapter on heater wiring (see Morgan Jones' books), but here's a few tips.

  If all your heaters are wired in parallel, there will be very little effect the actual sequence will have on operation. Sure, there will be a little voltage drop across the 18 gauge wires, but I don't think 0.1 or 0.2 volts will kill you. Initially I would think you would wire the smallest current draw loads first, with the big loads last in the train. This would make the smallest loads have the least affect from the big ones. But then again, the real goal I would pursue is to use the least amount of wiring. This would probably not result in the desired sequence.

  If you are that concerned about voltage drop, consider separate runs to each tube or set of tubes. Also, note that a 6.3V 8A winding is typically rated to output 6.3V at rated load. Being that you are only pulling 25% of this, your actual applied voltage will probably be greater, maybe 6.6V.

  If you find this to be the case, consider a series resistor(s) to bring the voltage into spec. Some would insist on a resistor in each leg; if you have a grounded center tap, this might not be a bad idea.

  Finally, if you have any elevated cathodes, an elevated heater voltage might be worthwhile. This would require another transformer winding.

  Good luck
  
  

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  • Re: I think you're on the right path - LowRedMoon 10:40:20 02/26/07 (1)
    In Reply to: I think you're on the right path posted by KurtP on February 25, 2007 at 17:05:05:

    That all makes complete sense and gives me a few ideas. I have both of Mr. Jones' books but didn't encounter much info on this particular subject. Perhaps I must take another look.

    I have a pretty hearty stock of resistors if I need them. Are there any types of composition that you would recommend NOT using for this application?

    Thanks - Adam
    
    

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    • Resistors aren't all that critical here - KurtP 12:05:52 02/26/07 (0)
      In Reply to: Re: I think you're on the right path posted by LowRedMoon on February 26, 2007 at 10:40:20:

      For starters, determine the size and power rating you need. I like to run my resistors at no more that 20% of their wattage rating, to keep temperatures under control and limit the positive tempco most resistors exhibit. In critical places, I go for 10%. Heater supplies are not critical; you will be more subject to line voltage variations.

      I would likely end up using a standard cheap wirewound; they are very sturdy and come readily in the sizes you are likely to require (somewhere in the <1 ohm range). Non-inductive is unnecessary; your source has lots of L anyway.

      I would remind you of the importance and sonic benefit of elevating heaters where necessary. Don't underestimate this consideration. Jones spends a lot of time discussing heaters in the chapters where he actually steps you through building an amp, though I think there are some places prior where he discusses some other issues. Personally, I don't buy into his THINGY design; unneeded, IMO.
      
      
      

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