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Schematic Help

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Atomic_Sheep, Sep 8, 2017.

  1. Atomic_Sheep

    Atomic_Sheep Member

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    I started building a clone and encountered some questions regarding the schematics:

    1.) Why does this capacitor have a rating of 1kV?

    2.) What unit is next to the 25? It doesn't look like the V just has cut off tops. If you compare to other V's, the Vs have a rather pointy end, this one looks more like a u but that doesn't make sense, at least to me.

    3.) If there are no units, then I presume for capacitors we're talking farads and for resistors we're just talking ohms?

    4.) Why is one PF and the other one is uf? Why is there a difference in capitalisation of the farads?

    I'm no electronics expert, learning as I go along, but details matter and I don't want to blow anything up.
     

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  2. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Most of your questions are simply answered as typos or sloppy review. We all make such mistakes.
    @#2: The unit appears to be "V" for volts. That is not surprising, as 6800 uF is a fairly large capacitor.
    @#3: No units is most likely uF for capacitors. Agree that a resistor without a unit is in ohms. Note that "3K3 " means 3.3 kohms
     
  3. Les Jones

    Les Jones Well-Known Member

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    1 The voltage across the capacitor will be 488 volts. It could be higher than this as the transformer will probably give more than 345 volts when lightly loaded. So you would probably choose one with at least 700 volts rating. Probably 1Kv is the next highest voltage rating after 500 volts.

    2 V (For volts.)

    3 I think for capacitors it will be uF in the case of C13. When it is in hundreds I think it will be pF. For resistors I think it will be ohms.

    4 It is easier to write 47 pF rather than 0.000047 uF and it is easier to write 10 uF rather than 10000000 pF I don't think the person drawing the schematic meant any difference between upper case and lower case for Farads.

    Les.
     
  4. dave

    Dave New Member

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  5. Atomic_Sheep

    Atomic_Sheep Member

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    Thanks for the prompt response guys!
    I guess good and bad news. Makes me worry about how reliable these schematics are :). When I talked about blowing up components, I was joking, now I have a feeling that jokes aside, it can happen.
    I had a think and at the moment I'm guessing but I think I'm going to assume caps lock was on when 47PF was typed. Because there's a whole bunch of 47pf capacitors in the schematics, but this is the only 47Pf/PF capacitor. That's a very big difference and I have a feeling caps lock was to blame. I'll put this on my to do list i.e. to see whether I can figure out the logic behind the electronics.
    Back to it!
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Why are you trying to make a circuit with parts that are about 80 years old?
     
  7. AnalogKid

    AnalogKid Well-Known Member

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    1. 1 kV was a common rating for small capacitors in tube days.
    2. 6800 uF, 25 V. Yes, that is a V.
    3. No units = microfarads C13 is 0.22 uF.
    4. Because picofarads are 1,000,000 times smaller than microfarads, and writing 0.000000047 uF on a part is hard.

    4a. Sloppy reference designation practices. There actually is a written set of standards for using the abbreviations of scientific quantities. For example, volts, ohms, henries, and farads are not capitalized when spelled out, but the abbreviations, V, <omega>, H, and F, are capitalized because those quantities are based on proper names. The abbreviation for siemens is S, but for seconds it is s.

    But - people take liberties in schematics to make things more legible. It is common to see all capital letters in all abbreviations.

    ak
     
    Last edited: Sep 8, 2017
  8. Les Jones

    Les Jones Well-Known Member

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    Hi AK,
    I think you have made a typo on answer 4 1000 should be 1000000

    Les.
     
  9. AnalogKid

    AnalogKid Well-Known Member

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    Oops. Edited.

    ak
     
  10. Atomic_Sheep

    Atomic_Sheep Member

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    Because the sum of those 80 year old parts (I'm guessing you're referring to the tubes?) come at a modern price of $5,000 RRP and I don't fancy spending that much for them :). But I'm sure it's not a simple case of finding any old parts for this thing to reproduce the tone of the original, but there's a lot of unknowns currently for this project for me.

    Great thanks!
     
    Last edited: Sep 8, 2017
  11. schmitt trigger

    schmitt trigger Active Member

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    The schematic has several issues that would have been caught if it had been properly reviewed.

    For instance, there are several JFETs whose gates appear to be not connected anywhere.
    And which don't have reference designators, either.
     
  12. AnalogKid

    AnalogKid Well-Known Member

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    The FETs are analog switches driven by a part of the schematic not shared. But I agree with the missing ref designators and signal names.

    AND, Why are there *three* sets of tone controls plus a multi-band graphic equalizer?

    ak
     
  13. Atomic_Sheep

    Atomic_Sheep Member

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  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It's an instrument amplifier, it's good to have as many options as possible, as you're trying to colour the sound to get what you want. It's also quite likely the amp was available with or without the graphic, hence the tone controls were there already :D
     
  15. AnalogKid

    AnalogKid Well-Known Member

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    The graphic eq might be there to reduce feedback.

    ak
     

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