• I have to confess... - Caucasian Blackplate 15:44:01 03/06/08 (1)
  In Reply to: RE: Up and running posted by awsjr on March 06, 2008 at 07:27:03

  When I built my first couple of Foreplays, I really didn't think much of the parts that went into them. I did a lot of substitutions for resistors and caps, especially the resistors on the C4S boards. In the end, a stock FP2 with anticipation ended up sounding much better. When I got down to it, the resistors in these kits are quite carefully selected. I also figured out that the power supply capacitors in many of these kits are actually some of the most expensive electrolytics you can find in that case size, short of Black Gates. The same goes for the kit wire, I just priced a couple of 100 ft. spools for myself, and I was absolutely shocked how expensive the teflon hookup wire is. Anyway, my point is, go ahead and experiment, but build it as stock as possible first so you know if you're making headway.
  -Paul
  
  

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  • RE: I have to confess... - awsjr 05:59:27 03/07/08 (0)
    In Reply to: RE: I have to confess... posted by Caucasian Blackplate on March 06, 2008 at 15:44:01

    hi Paul....thanks....thats great perspective from someone who's built their share of kits....much appreciated -Al
    
    

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• RE: Up and running - Doc B. 09:11:43 03/06/08 (4)
  In Reply to: RE: Up and running posted by awsjr on March 06, 2008 at 07:27:03

  Hopefully you are considering power dissipation and voltage ratings when you are planning to make substitutions of, for example, two 1/2W resistors in series. Those resistors we just threw together are chosen with those parameters in mind as well as their material composition.
  
  

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  • RE: Up and running - awsjr 11:43:06 03/06/08 (3)
    In Reply to: RE: Up and running posted by Doc B. on March 06, 2008 at 09:11:43

    perhaps "threw together" was not the best expression for the efforts you made to develop this modification....but it is interesting that you are suggesting / recommending I consider power dissipation and voltage ratings while offering no details regarding the choices made for the circuits....or for example, how a caddock mk132 316k or caddock mk132 75k might be poor substitutions for some of the original resisters....can you provide some information behind the decision to parallel or put resisters in series ?
    is your example indicating 1w is needed for the series resisters ?
    
    

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    • RE: Up and running - Doc B. 07:20:39 03/07/08 (0)
      In Reply to: RE: Up and running posted by awsjr on March 06, 2008 at 11:43:06

      Power dissipation across a resistor can be calculated by dividing the square of the voltage drop across it by the resistance. Resistors should be rated for at least 2X the power to be put through them, and PJ prefers 3X as a safety margin. You can use the voltages and resistances listed on the schematic to calculate the power dissipation requirement of the resistor as well as it's voltage rating. However I believe you will find the work has already been done for you on the SR45 schematic on page 4 of the manual. Power ratings for the resistors that are running relatively high dissipation are already spec'd on the schemo. Either it will not be easy or it will not be inexpensive, for example, to locate a 75K resistor rated for 6W and 5% tolerance. It may be far easier to find a reliable 150K 3W that can be paralleled. If you use a Caddock, make sure it can handle 6W of dissipation in that application.

      Voltage ratings must take into consideration the actual voltage that the resistor will see through the startup cycle. In the case of the Paramount circuit we use a resistor with 750V rating in one location, that being the 300K. Many resistors are rated for 500V or less and in these cases two 500V rated resistors in series can be used to handle startup voltage peaks that go above 500V.
      
      

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      Edits: 03/10/08
    • RE: Up and running - nullspace 12:54:31 03/06/08 (1)
      In Reply to: RE: Up and running posted by awsjr on March 06, 2008 at 11:43:06

      From my reading of the schematic (which may or may not be correct)...

      The film resistors are placed in series (the 2x158k) because generally film resistors are rated for something like 250vDC or less, and these guys have > =320vDC across them collectively. You'll need to check the voltage rating for the Caddocks to see if they work here.

      The wirewounds placed in parallel (2x150k) need a healthy rating, so the 6W rating noted. A Mills 12W would probably work here ratings-wise, but will it fit?

      No matter what component we're talking about, it's always best to check voltage/ wattage ratings.

      Regards,
      John
      
      

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      Edits: 03/06/08
      • RE: Up and running - awsjr 01:53:04 03/07/08 (0)
        In Reply to: RE: Up and running posted by nullspace on March 06, 2008 at 12:54:31

        thanks John...appreciate your input -Al
        
        

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