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Given Values??

Discussion in 'Shock Brother's DIY Amps' started by alias23k, Jul 25, 2009.

  1. alias23k

    alias23k Tele-Meister

    Jul 3, 2009
    sweaty southeast
    Hey Guys,
    I'm dabbling in amp building (don't worry, doin' research before i kill myself) and been reading some schematics. One thing i noticed is some of the resistors and caps don't have complete values. Such as some resistors only read 330k or 22k and some caps read 22uf or .01. Is there a common vlaue for these like for the resistors is 1/4 watt and for caps, maybe 25v. or does it depend on the make up of the diagram or something else. thanks in advance.
  2. celeste

    celeste Friend of Leo's

    Jun 24, 2006
    You can usually calculate wattage, then derate by 50%. the 50% figure is a conservative value to increase reliability. Noise performance is also improved for a given value a given current flow and given construction as wattage goes up, so you may want to go even bigger. As my stocks are depleting, I am just buying 2w resistors as my general use resistor.

    Voltage is determined by the highest value the cap will see. You have to consider what happens during warmup as well, before the tubes start to conduce, unless you are using a controlled warmup rectifier like a GZ34. In cathode bypass, you really have to calculate the voltage drop across the cathode resistor. Most of the time 35v is enough, often 25 is enough, but I have an amp beside me that requires 75v caps and it really wants them to be 2000uf or more
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