About Copper Oxide rectifiers

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About Copper Oxide rectifiers

Post by Resistance is Futile on Sat Nov 06, 2010 10:05 pm

Didn't know this. Sounds better than the selenium type. I know they were used in older meter movements.

Copper Oxide Rectifier

With the use of the copper oxide rectifier in a recent receiver of the portable type, their popularity will possibly be revived for radio purposes, as in the days when they supplied rectified a-c for the fields of loudspeakers.

Any device which offers a high resistance to the flow of current though it in one direction, and a comparatively low resistance to the flow of current to it in the opposite direction, makes a good rectifier for an alternating voltage. This is the case of the dry contact rectifiers, such as the copper oxide type. The copper oxide rectifier is made in the form of a copper disk, coated on one side by a layer of copper oxide. The copper oxide is plated with nickel to allow good external circuit contact. The juncture of the oxide and copper offers a low resistance to the flow of current from the oxide to the copper, but a high resistance to the flow of current in the reverse direction. The detailed operation of this device is complex, but in general it involves the formation of thin films at the junction of the oxide and copper in which the molecules are so polarized that the transfer of electrons in one direction requires much less work than a similar transfer in the opposite direction.

Copper oxide rectifiers possess a definite breakdown voltage and breakdown temperature. If either critical value is exceeded, the rectifier will pass current freely in both directions. After the unit is cooled or the high voltage removed, it will immediately function again as though it had not been overloaded.

The copper oxide rectifier can be connected in either the half-wave rectifier or full-wave rectifier circuit.

The test for proper single disk operation is to impress a ½ -volt d-c across the disk in the conducting direction; then the current should read should read 0.5 amperes or more. By reversing the battery polarity a current of no more than 2 ½ Milliamperes should flow when 2 volts is applied to the disk in the non-conducting direction.

This was copied from the General Electric Company Electronics Department, booklet #175-3012A THE ABCs of RADIO (copyright-1943)
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Re: About Copper Oxide rectifiers

Post by denver on Sat Nov 06, 2010 10:26 pm

Wow interesting ,all that reading made my head hurt cyclops No really very interesting i book mark lots of post this will be one.
Thanks.
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Re: About Copper Oxide rectifiers

Post by tube radio on Sun Nov 07, 2010 5:58 pm

Very very intersting.

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Re: About Copper Oxide rectifiers

Post by Bill Cahill on Sun Nov 07, 2010 6:14 pm

Actually, they are about as bad as selenium, and, get eaky, and, weak.
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Re: About Copper Oxide rectifiers

Post by electrojim on Sun Mar 06, 2011 11:42 pm

By today's standards, copper oxide rectifiers are virtually useless for most power-handling applications. Mostly, their reverse voltage is low, requiring 'stacking' for use in all but small-signal circuits. HOWEVER, they have very nice forward-conduction charactertistics that make them ideal for certain "variolosser" applications, and as such they were used by Western Electric for many Bell System compander circuits. What's more, they can be fabricated on the kitchen table without too much trouble or mess. Some crystal radio experimenters report better-than-germanium results as detectors, too!

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Re: About Copper Oxide rectifiers

Post by jtauser on Mon Feb 04, 2013 1:07 am

I'm working on an old DeForest's VOM which was never completed. I have acquired many of the DeForest Home Laboratory Lessons and I have the one to finish the meter.

It calls for an "Instrument Rectifier", which the schematic shows as two diodes in series tapped in the center. The pictorial assembly diagram shows a rectifier stack like a selenium but this copper oxide thing came up in a Google Search.

Your forward bias information is very helpful - I should be able to re-create this with a couple of germanium diodes.

Joe T.
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Re: About Copper Oxide rectifiers

Post by electrojim on Mon Feb 04, 2013 3:03 am

Germaniums should work just fine, and they won't change as the years drag past. Let me know if you need some, I acquired a good quantity; they are generally available on eBay as well.

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Re: About Copper Oxide rectifiers

Post by Guest on Mon Feb 04, 2013 1:50 pm

I have a GE model 250, a late forties rechargeable 2 volt radio that has a copper oxide rectifier.

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Re: About Copper Oxide rectifiers

Post by Ragwire on Sat Jun 15, 2013 11:06 pm

If I may revive this old thread...I was aware of these, but I think zinc oxide and lead diodes are easier to make. I don't know about power rectification, but they make good detectors. I have made power rectifiers from a glass (real glass) of water with about a tablespoon of baking soda in it. One conductor...the anode I think...must be aluminum. The other can be almost any metal. They are kept separate in the solution by an inch or two. A 60 watt incandescent lamp makes a good load to form the diode with by hooking it up in series with the diode at 120VAC. It will glow brightly at first, and then dim as the oxide is formed on the aluminum and it begins receiving only half wave power.
Once formed into a diode, it stays that way after power is removed...at least as long as I have let it sit...like for a few days.

Warning: This works if you do it right and it is fairly easy to do right, but you are working with lethal voltages around conductive water solutions and open containers. It may also produce fumes, but I have not read of any or detected any. Read up on it first, and only try it at your own risk.
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Re: About Copper Oxide rectifiers

Post by Bell Ringer on Fri Apr 25, 2014 1:38 am

Copper Oxide Rectifiers Seemed to work well in old school intercom systems.After working around intercom power supplies ( I think around 24 volt ) for many years I can only think of one or two giving us any trouble. I think the forward voltage drop being higher than new diodes limited the current when the output became shorted or leaky. I have seen them have a shorted intercom line for several weeks during the summer and after fixing the phone line in sept work fine after school started back up. We had maybe 25 or so schools using them and also very high quality caps .Only changed a couple of diodes and a few caps in 32 years. They were about two and a half inches in dia. and 10 or 12 wafers stacked. Just thinking of the good old days when life was simple.

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Re: About Copper Oxide rectifiers

Post by Ragwire on Mon Apr 28, 2014 9:51 am

Bell Ringer wrote:[...]Just thinking of the good old days when life was simple.
And when school didn't start until September...

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Re: About Copper Oxide rectifiers

Post by Bill Cahill on Mon Apr 28, 2014 10:45 am

...And, children in general respected their parents........  Sad 

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