Circuit questions

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by stebnera, Jan 27, 2008.

  1. stebnera

    stebnera Member

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    So, I've followed the schematic all the way through the Earth Revival and there are a couple of things that are different, but I'm not familiar enough with amplifier circuits to know if the differences are good, bad, or otherwise.

    The first area of concern is the filter and the location of the standby switch. I'm looking for advice as to leave it the way it is (in red) or return it to the state of the original schematic I received.

    The second thing that is puzzling to me are the resistors located below Q5 on the schematic. The original had a 3.3K in series with either a 100 ohm or a 100 K, it was hard to read the print, but I'm going with 100 K since that's what's in there. Is there really a big difference between 100K and 103K? Also, there's no spot on the PCB for the 3.3K resistor. There is, however, a 15K piggybacked on the 100K, which gives a total resistance of 13K. Should I leave this configuration, or just stick to the 100K? What does changing the resistance at this point in the circuit achieve?

    I think I can swing the rest, most of the other things aren't of concern, they just seem that some of the components were replaced along the line and exact replacements weren't available so they used the next closest thing. If anyone has any other suggestions though, I'd appreciate them. The 4 resistors I have noted as "40pF ?" aren't really 40 pF I don't think, but the multimeter I have at home won't measure capacitance and those values are what I could make of the capacitance calculator I found, as they are old rectangular ceramic drop caps with color bands painted on them.

    [​IMG]

    Thanks,
    Aaron
     
  2. Chrome Dinette

    Chrome Dinette Silver Supporting Member

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    I think I used to have one of these, 2x12 combo, right?

    100k vs 103k shouldn'tmake much of a difference.
     
  3. stebnera

    stebnera Member

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    My friend's is actually a 4 x 10, but I think it's the same circuit.
     
  4. Chrome Dinette

    Chrome Dinette Silver Supporting Member

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    If the amp has wheels on it, I suggest you push it out into traffic.




    Just kidding, but trying to refurb this might be more heartache than it is worth.
     
  5. stebnera

    stebnera Member

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    At this point, it's not really about worth as much as it is the learning experience. This is what I'm doing for stress-relief & enjoyment, it's not a financial investment.

    The main thing I'm not sure about is the filter circuit, and if I should keep it wired the way it is, or change it back to the way it's drawn in the schematic. If there's no potential for disaster with either wiring, I have no problem just trying both ways and seeing what changes. It doesn't seem to me that there's a potential for disaster with either wiring, but I'm new at this so I'd rather ask.
     
  6. Chrome Dinette

    Chrome Dinette Silver Supporting Member

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    The two 220k resistors in the filter circuit are meant to be wired in parallel with two series wired caps. Look at some other schematics if you are not sure what I mean.
     
  7. phsyconoodler

    phsyconoodler Member

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    those two rsistors decouple the filter caps./they need to be like Fender does it.Go to www.schematicheaven.com and look at Fender's schematics for a super reverb and you will see how it's done.
    The original lifts the centre tap of the diode bridge rectifier.That's an acceptable standby.No need to change it.
     
  8. stebnera

    stebnera Member

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    great, thanks so much
     

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