Germanium Diodes

Learn about the advantages of Germanium Diodes

Diodes are a very important component of most alternative energy generating systems - for example in PV solar panels (1) they are used to stop energy being radiated back out into the night sky from the battery bank (2), and in wind turbine (3) generators they are used to rectify (4) AC into DC electricity.

Most diodes are made of silicon because of its ease of processing and stability, however they have one disadvantage: a silicon diode has a forward voltage drop of around 0.7 volts. This means that if you had a 7.0 Volt rated solar panel charging a battery via a silicon diode, only 7 - 0.7 = 6.3 Volts would be seen by the battery - the remainder is lost as heat in the diode.

In a Bridge Rectifier (5) the current passes through two diodes. Therefore the total forward voltage drop is a whopping 1.4 volts - a significant amount in low voltage systems.

Germanium Diodes

A Germanium Diode (such as the 1N34 pictured above) will typically have a forward voltage drop of just 0.3 volts which means they are much more efficient. Older germanium diodes had a larger leakage of current at a reverse voltage, but now American Microsemiconductor and others supply a range of improved low current leakage germanium diodes. Diodes such as the most common 1N34A can cost as little as 5 pence each.

Buy Germanium Diodes

It is not always easy to find germanium diodes as they are not a very popular item. One of the best ways to obtain them is to purchase vintage stock made available for sale on eBay (6).

At the time of updating this article (August 2008) there were OA47, OA81, OA90, OA91, OAZ210, IS689, 1N34A, 1N42, 1N60, AAZ17, and AA119 germanium diodes all listed for sale - some new and some vintage / used.

Click here to search eBay UK for germanium diode (7), or here to search eBay USA for germanium diode (8).

In the UK Rapid Electronics (9) often have one or two germanium diodes (10) - click to view their latest listings.

More Information about Germanium Diodes

While silicon diodes are resistant to the heat from soldering, germanium diodes can very easilty be damaged. Therefore a crocodile clip or other suitable heat sink should be clipped onto the lead between the diode body and the joint to be soldered.

An interesting article about the practical use of Germanium Diodes in a crystal radio set (11) is here, and discusses the forward voltage drop of a selection of germanium diodes in real world testing. The OA47 came out tops with a forward voltage drop of under 250mV.

Web Link References

(1) http://www.reuk.co.uk/Diodes-and-Solar-Panels.htm
(2) http://www.reuk.co.uk/Interconnecting-Batteries-for-Battery-Bank.htm
(3) http://www.reuk.co.uk/wind.htm
(4) http://www.reuk.co.uk/Bridge-Rectifier.htm
(5) http://www.reuk.co.uk/Building-Your-REUK-3-Phase-Bridge-Rectifier.htm
(6) http://rover.ebay.com/rover/1/710-53481-19255-0/1?type=1&campid=5335956244&toolid=10001&customid=germanium+diode
(7) http://rover.ebay.com/rover/1/710-53481-19255-0/1?type=3&campid=5335956244&toolid=10001&customid=germanium+diode&ext=germanium+diode&satitle=germanium+diode
(8) http://rover.ebay.com/rover/1/711-53200-19255-0/1?type=3&campid=5335956244&toolid=10001&customid=germanium+diode&ext=germanium+diode&satitle=germanium+diode
(9) http://www.awin1.com/cread.php?awinmid=1799&awinaffid=80045&clickref=&p=http%3A%2F%2Fwww.rapidonline.com%2F
(10) http://www.awin1.com/cread.php?awinmid=1799&awinaffid=80045&clickref=&p=http%3A%2F%2Fwww.rapidonline.com%2Fsearchresults.aspx%3Fstyle%3D0%26kw%3Dgermanium
(11) http://members.tripod.com/~baec/articles/crystal.htm