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Circuit symbol CR

  1. Jun 11, 2012 #1
    Circuit symbol "CR"

    I have seen in some old schematics that diodes are labeled "CR" as a ref designator instead of D. I am just curious what the intention of this was since I have never seen a diode labeled with CR until now.

    CR = crystal rectifier or current rectifier?
  2. jcsd
  3. Jun 11, 2012 #2
    Re: Circuit symbol "CR"

    Yes CR harps back to the days when you had a choice valve rectifiers or the new fangled 'crystal' ones.

    I have also seen it used to describe thyristors/triacs under the genral heading 'controlled rectifier'
  4. Jun 11, 2012 #3
    Re: Circuit symbol "CR"

    Thanks for the confirmation :)

    How far back is the days when you had this choice? I am confused because I thought history went as:
    crystal rectifier (cat whiskers?) -> vacuum tubes -> semiconductors, what we call diodes

    or does crystal just refer to the crystalline silicon semiconductors they started using after vacuum tubes?
  5. Jun 11, 2012 #4
    Re: Circuit symbol "CR"

    Commercial solid state rectifiers were of two flavours. Point contact diodes for signal purposes and selenium rectifiers for power. Germanium and silicon power rectifiers came later.

    The cats whisker was a 'roll you own' point contact diode for boy scouts and WWI/WW2 spies, Fleming's original experiments were with vacuum diodes. De Forrest introduced the triode I believe.

    Valve technology continued well after the introduction of semiconductor components and is still not finished yet.


    Early semiconductor rectifiers were also for relatively low voltage compared to valve ones so could not manage say a 350 volt supply. This prolonged the use of valve rectifiers until the advent of lower voltage valves and higher voltages semiconductor technology.
    Last edited: Jun 11, 2012
  6. Jun 11, 2012 #5
    Re: Circuit symbol "CR"

    I used to repair antique radios as a hobby when I was in high school. Most of them used the 35W4 tube to rectify AC mains into 90VDC (no isolation transformer, one side of AC mains connected directly to chassis!). Newer models (meaning built in 60s vs 50s) used a selenium rectifier.
  7. Jun 11, 2012 #6
    Re: Circuit symbol "CR"

  8. Jun 12, 2012 #7
    Re: Circuit symbol "CR"

    They were definitely not antique when I was messing with them. The older ones were probably only 15 or 20 years old when I got my hands on them. Figured they would be considered antique by now since I am pretty well antique myself.
    A number of them were given to me dead, and just had a bad 35W4. I wonder if high failure rate is why they switched to selenium.
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