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Old 3rd Oct 2022, 12:00 am   #1
markfff
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Default Copper Oxide Rectifier

I'm involved in a project to restore a WWII era flight simulator, and came across something labelled a copper oxide rectifier in one of the power supplies. This device is wired as a full wave bridge with a 50uf 50V capacitor across, so I'm thinking fairly low voltage and low current.

It's too early in the project to apply power yet, but being around 80 years old I'm thinking this part might be a bit dodgy. Can anyone explain the characteristics of those diodes, and is there any pitfalls or reason not to replace it with a silicon bridge?

Thanks,
Mark
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Old 3rd Oct 2022, 7:49 am   #2
Diabolical Artificer
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Default Re: Copper Oxide Rectifier

No expert but AFAIK these were fitted to VU meters as they have very low voltage drop, so maybe schottkey diodes would be a good replacement.

Andy.
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Old 3rd Oct 2022, 9:07 am   #3
Ed_Dinning
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Default Re: Copper Oxide Rectifier

Generally a very low forward voltage that is pretty linear with current, but lowish reverse voltage. Favoured for demodulation applications.

Quite a cheap process so actually used in some early electric train sets in the power supply.

In your power supply I suspect various types could be used but the rectified output voltage may be lower

Ed
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Old 3rd Oct 2022, 3:32 pm   #4
John_BS
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Default Re: Copper Oxide Rectifier

There's an interesting book available to download FoC which gives some useful data on copper oxide rectifiers. The author states that copper oxide diodes are quite reliable provided they're not overloaded, so the bridge may well be OK.


"Metallic Rectifiers and Crystal Diodes" Theodore Conti

John
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Old 3rd Oct 2022, 3:59 pm   #5
The Philpott
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Default Re: Copper Oxide Rectifier

The smaller ones are very simple- four copper plates that have been oxidised on one side. If yours hasn't been abused or started to corrode then it may well be serviceable. 'Scope the output?

Dave
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Old 3rd Oct 2022, 4:19 pm   #6
G6Tanuki
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Default Re: Copper Oxide Rectifier

Some of the very small ones - like the 'westector' - are little copper pills held in a plastic tube. As well as being used as detectors they were also sometimes found in low-voltage-DC grid-bias supplies, where it would have been wasteful to use a valve rectifier [with its attendant heater load] if you only needed a few milliamps at a few volts.
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Old 3rd Oct 2022, 4:47 pm   #7
Craig Sawyers
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Default Re: Copper Oxide Rectifier

The rectifier for AC ranges in the early AVO8's was a copper oxide one.

Craig
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Old 3rd Oct 2022, 8:45 pm   #8
markfff
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Default Re: Copper Oxide Rectifier

Thanks all for the info. My best guess at this point is that the supply is used either for grid bias or a rerference source somewhere else in the system. Right now we're still figuring things out, but since these seem to be reliable with good longevity (thanks John, for the book) I think we'll keep it, and see what happens when we're ready to test the unit.
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Old 4th Oct 2022, 11:27 am   #9
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Default Re: Copper Oxide Rectifier

I'm sure you don't need reminding, but the 50uF capacitor certainly should be changed!

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