Point contact diode's colour rings

[jpgandr]

Some point contact diodes have color rings (as shown in pic.) instead of printed numbers and letters code (as 1N34A).

What does that color code mean?

[FERNSEH]

Certain Mullard crystal diodes indicate the type number by the use of colour rings. For example: violet black indicates that the diode is a OA70.
The OA79 is violet white.

It's likely the diode in the attachment was not made by Mullard.
The broad yellow band and will indicate the cathode. According to the colour code: 4 2 5. Is there such a thing as a 1N425? Or perhaps 1S425.

DFWB.

[jpgandr]

Thank you for your reply.

So numbers here are color coded like resistors ,red green = 25.
Wide ring indicates cathode.

[jpgandr]

I didn't find 1N425 or 1S425 , I guess it can be any xx425 !

[MotorBikeLes]

Without going and digging out old circuits, I can't give specific examples, but I recall quite a few diodes in older Grundig (hybrid) colour TVs used diodes with numbers, and those numbers can be read off the diodes using usual resistor colour codes. If I get chance, I will go and give some examples.
Just remembered, TD190 was one, so colours would be brown/white/black. There were others.
Les.

[jim_jobe]

Presumably some "computer diodes" had house codes as well? I have some reclaimed from old printed circuit boards that seem to be like this.

[turretslug]

Quite a few NOS here of that yellow-brown-yellow-grey stalwart, the 1N4148 here, though the brown band, in particular, seems to have flaked badly on most.

Shame this form of ident wasn't followed more often, there'd be some quite pretty diodes out there!

[jpgandr]

Finally found it !. It is a CV425 modern version ! according to this site

http://www.tubecollector.org/cv425.htm

The problem is that you have to figure out the letters (xx) in xx425 as
xx can be 1N (American),1S (Japanese) ,CV UK-Military CV-series,OA,AA,.... (European).

Thank you all for your help.

[Herald1360]

Good spot!

I found a white brown yellow in my bits but no yellow brown yellow greys only the alphanumeric variety.

Have you checked Vf to confirm its germaniousness?

[jpgandr]

It is not with me right now,i bought NOS point contact diodes recently most of them with no marks at all ,few made in USSR with code on their flat terminals and those with color rings.
Yes Herald1360 you are right , i should have measured its forward voltage to see if it is germanium (around 0.3 volt) or not but i was in a hurry so i only took a pic. of one of those with color rings.

[FERNSEH]

A Mullard OA79 with the coloured bands violet and white.

DFWB.

[jpgandr]

I can not remember any point contact diode that was not germanium ,most were AA,OA,...
but no BA ,all i can recall is while comparing some point contact diodes long time ago searching for the lowest forward voltage 1N34A had the lowest (0.28 V) while all others were 0.29 to 0.35 V except one unmarked but point contact measured 0.6 V !!!

I can not remember any point contact diode that was not germanium

Some (if not all) of the mixer diodes used in WW2 radar where silicon point contact as where ones used in the old Trinitron TV tuners.

[FERNSEH]

The OA47 gold bonded diode. For switching applications.

http://www.radiomuseum.org/tubes/tube_oa47.html

DFWB.

[jpgandr]

According to datasheet OA47 has Vf=0.34 V @ If= 1mA
,Vf=0.45V @ If = 10 mA hence this Vf=0.54 V mentioned in radiomuseum site is @ If =30 mA.

[Herald1360]

Originally Posted by FERNSEH

The OA47 gold bonded diode. For switching applications.

Also good for crystal sets. Very low Vf in the uA forward current region.

[G6Tanuki]

OA47 was always my favourite for use in noise-limiters/noise-gates - very predictable (and thermally-stable - important when designing mobile/portable stuff) turn-on threshold, and nice low reverse-leakage too.

I guess today I'd use a Schottky diode.