Circuit Symbol CR: Decoding the Mysterious Ref Designator in Diode Schematics

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Discussion Overview

The discussion centers around the use of the circuit symbol "CR" as a reference designator for diodes in schematics, particularly its historical context and implications. Participants explore the evolution of rectifier technology, including crystal rectifiers, vacuum tubes, and semiconductor diodes.

Discussion Character

  • Historical
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that "CR" stands for crystal rectifier or current rectifier, indicating a historical reference to older rectifier technologies.
  • Others note that "CR" has also been used to describe thyristors and triacs under the term "controlled rectifier."
  • One participant expresses confusion about the timeline of rectifier technology, questioning the historical sequence from crystal rectifiers to vacuum tubes to modern semiconductors.
  • Another participant provides details on the types of early solid-state rectifiers, mentioning point contact diodes and selenium rectifiers, and discusses the continued use of valve technology alongside semiconductors.
  • A participant shares personal experience repairing antique radios, noting the use of the 35W4 tube and the transition to selenium rectifiers in newer models.
  • There is a reflection on the perceived age of the radios, with a participant humorously commenting on their own age in relation to the devices.
  • One participant speculates that the high failure rate of the 35W4 tube might have contributed to the switch to selenium rectifiers.

Areas of Agreement / Disagreement

Participants express various viewpoints on the historical context and terminology related to the "CR" designation, with no clear consensus on the specifics of the timeline or the implications of the term.

Contextual Notes

Participants reference various types of rectifiers and their applications, but the discussion does not resolve the uncertainties regarding the historical timeline or the definitions of terms used.

DragonPetter
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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?
 
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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 general heading 'controlled rectifier'
 


Studiot said:
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 general heading 'controlled rectifier'

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?
 


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.

Edit

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.
 
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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.
 


antique...vs 50s

 


Yea,
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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