diode question

[p.larner]

I have just brought some cv7130 diodes,this is the military number for an oa91,the vf tests at about 700mv,is this not too high for these, i thought the vf should be in the 2to 3 hundred millivolt range,have i got duds?.

[Ian.M]

Most germanium diodes that aren't N.O.S in original packaging from a reputable specialist supplier are fake.

https://www.eevblog.com/forum/beginners/is-it-really-germanium/
https://www.eevblog.com/forum/beginners/silicon-germanium-diode/

[p.larner]

these dioddes are in the original wax paper packets,ex mil but i expect these are old rejects,going to contact the seller and see what he says,i dont imagine a good genuine germainium point contact diode should have a vf higher than an average si diode!,

[wasedadoc]

I was using CV7130 diodes (glass body painted white with red ring and red lettering) back in the early 1970s.  A few hundred millivolts forward voltage at low current.

[Jwillis]

It's a misconception that all germanium diodes will have a very low forward voltage of 2 to 300mV.  OA91
Your CV130 diodes are fine.

[Ian.M]

Check reverse leakage vs temperature (but don't get them too hot - stay under 75 °C).   The genuine Germanium part will have a much higher reverse leakage than a comparable (similar current and reverse voltage rating) Silicon PN or Schottky part, and be more temperature sensitive.

[CaptDon]

I can still find the capsule style 1N23E and 1N23ER brand new in the aluminized packaging from WWII and Vietnam era X-Band radar surplus. Sadly, due to age their reverse leakage is so high that the recovered I.F. signal is nearly useless. I find most of the genuine 1N34's that can be traced back to the mid 60's are also nearly useless. Germanium just didn't seem to age very well including much of the PNP Germanium transistors in old military gear. 2N404? Many of the old V.O.M. meters would instantly harm microwave germanium diodes. The military had 'purpose built' testers for the 1N23 and 1N21 parts!!

[p.larner]

Well the seller replaced these iffy diodes,this was to build a swr sensor cct(see pdf),i tried 1n5711 diodes but found the return meter insensative,the new diodes now read about 0.3v diode drop,these are the oa91 diodes,the best i can get is two of them have a vf of 0.317v,will they work better than unmatched 1n5711 diodes,i have only matched the vf as i dont have a curve tracer,thanks in advance.also this is for hf 3.5-30 Mhz ok.

[p.larner]

well fitted the replacements but ref output is poor,would say two more turns on the lower torroid help?.

[Gyro]

Please don't double post. You've been told before, it annoys people...  https://www.eevblog.com/forum/rf-microwave/crazy-readings/msg5339780/#msg5339780