Author Topic: Shottky diodes instead of germanium in old analog meter  (Read 1628 times)

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Offline 001Topic starter

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Shottky diodes instead of germanium in old analog meter
« on: October 24, 2019, 01:55:34 pm »
Hi

I`m working with vintage AC voltmeter
The rectifier is two germanium diodes blown with galvanometer
I can buy new galvanometer but not new germanium diodes
Can I replace germanium with new shottky?  :-//
 

Offline 001Topic starter

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Re: Shottky diodes instead of germanium in old analog meter
« Reply #1 on: October 24, 2019, 02:10:46 pm »
 

Online iMo

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Re: Shottky diodes instead of germanium in old analog meter
« Reply #2 on: October 24, 2019, 03:34:11 pm »
The closest alternatives would be the BAT42/43/45/46. Unless you'll find the germanium ones, when pretty lucky
:)
PS: those BATxx diodes are small signal, max 30V or so, not to be used as rectifiers for higher voltages. Good around the galvanometer movement, imho.
« Last Edit: October 24, 2019, 03:38:14 pm by imo »
Readers discretion is advised..
 
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Offline duak

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Re: Shottky diodes instead of germanium in old analog meter
« Reply #3 on: October 24, 2019, 05:57:58 pm »
Pease had an article on various diodes' forward voltage characteristics.  I can't find the link to it now but I've attached a chart.

One thing to note is that large area devices, such as rectiiers, have a forward leakage current that can be significant at low voltages.  This current could affect the accuracy of the meter.
« Last Edit: October 26, 2019, 05:48:15 pm by duak »
 
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Offline 001Topic starter

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Re: Shottky diodes instead of germanium in old analog meter
« Reply #4 on: October 26, 2019, 02:54:30 pm »
awesome!
Thanx1
 

Offline bd139

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Re: Shottky diodes instead of germanium in old analog meter
« Reply #5 on: October 26, 2019, 04:54:42 pm »
I just jam a 1N270 in everywhere a Ge diode is used. Easy to get and seems to work fine with similar characteristic curves plus breakdown voltage is much higher than the average schottky diode.
 
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Offline 001Topic starter

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Re: Shottky diodes instead of germanium in old analog meter
« Reply #6 on: October 26, 2019, 05:51:01 pm »
I just jam a 1N270 in everywhere a Ge diode is used.

Thanx! Can You say about few examples?
 

Offline bd139

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Re: Shottky diodes instead of germanium in old analog meter
« Reply #7 on: October 26, 2019, 05:55:10 pm »
I've used them in RF detectors, good to VHF and to replace one inside a Micronta multimeter's AC circuit so similar use case to yours. I usually buy them from China. They are genuine Ge as they are much more temperature sensitive than an equivalent 1N5711 schottky. Main thing is if you have an analogue meter, you need a Ge diode rather than a schottky one as the scale is usually calibrated for the Ge diode curve.
 


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