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What is the effect on audio of using larger wattage resistor

  1. Nov 20, 2016 #1
    Hi,
    In general 1/2 watt resistors is what I see in tube guitar amps. I built one with 1 watt resistors and can not hear any difference. I assume shot noise will decrease with larger wattage values.

    Other than heat dissipation, how is a 1 watt resistor different from a 1/2 watt resistor.

    Thanks,

    Billy
     
  2. jcsd
  3. Nov 20, 2016 #2

    davenn

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    I wouldn't expect any difference
     
  4. Nov 20, 2016 #3
    Kinda what I thought...thanks
     
  5. Nov 20, 2016 #4

    Baluncore

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    There will be no immediate difference, but the choice of resistor will make a difference over time. It is usually not clearly specified, but many resistors are only rated at 100 volts. They creep towards open circuit if operated on higher voltages. Higher power resistors will usually have higher voltage specifications where the resistance and power rating necessitate that increased voltage. V=√(W*R).

    Higher power resistors will also be more reliable than standard due to lower thermal ageing. If you do not know the voltage rating of a resistor, assume 100 volts for axial and 50V for SMC. Use multiple series resistors to make higher voltage resistors.
     
  6. Nov 21, 2016 #5

    davenn

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    that's an old trick used by those of us that did tv servicing in days gone by
     
  7. Nov 21, 2016 #6
    Hi guys,
    On schematic I work from I don't think I have seen any notes pertaining to voltage values of resistors. Carbon Composition resistors were almost universally used in guitar amps made in the United States in the 1960s. While failures do occur from time to time, resistor failure in those amps is generally a function of some other component failing. Shorted tubes often take out the plate and grid resistors. There is not a lot of current in those circuits but the voltage is anywhere from 200VDC to 500VDC.

    I commonly see 1/2 watt metal film, and carbon film resistors used as plate resistors on output tubes running at 300VDC to 450VDC. Ohmite brand carbon comp resistors use to come in three different series and the series "OA" which was rated at 500V is no longer made as of 2014. Most of the various data sheets I have looked at indicate a voltage rating of 150V to 350V. Metal film datasheets I just looked at have around the same voltages ratings. Perhaps they will function at higher than stated values.

    I have not paid much attention to the voltage rating because I have not had any issues along those lines.

    As I am building one off custom turret board guitar amps, the cost of resistors is not really an issue. I had in mind to use 1 watt resistors as a general standard if in fact using 1 watt as opposed to 1/2 watt would not add some other negative condition to the build.

    In general, I am trying to define type, brand, and values standards of the components I am using. The only real cost issue relates to transformers and I don't yet know if the extra cost of Mercury Magnetics transformers is worth the money or not. The transformer issues I will post in another thread as it is anything but simple.

    Thanks,

    Billy
     
  8. Nov 21, 2016 #7

    Baluncore

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    You hope. Design to the component specifications, never beyond them. If there is no specification, do not use the component.

    Different construction resistors age at different rates under various conditions.
    If you base your choice of component on difference in price, what does that make your reputation worth ?

    Commercial and domestic products are now constructed to survive for only a three year warranty period.
    How long do you want your reputation to last ?
     
  9. Nov 21, 2016 #8
    Hi,

    As I said, price of resistors is not really an issue. Whatever grade of resistor was used in all the mid sixties Fender guitar amps are still working to this day without many issues.

    I have not made a serious search but all the 1/2 watt current day stuff I see has a voltage rating of around 350V. Tube amps run at voltages considerably higher than that. Thanks for the heads up and I will key the voltage issues into the search.

    Billy
     
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