Matching germanium diodes ? - UK Vintage Radio Repair and Restoration Discussion Forum

Dave UXB · 6th Aug 2011, 9:32 pm

Anyone know how to match a pair of germanium diodes for a RF bridge circuit please? In view of the scarcity of OA90/91, I plan on using 1N34A.

Richard · 6th Aug 2011, 9:46 pm

Hi

There are OA90 and OA91 diodes on Ebay

http://www.ebay.co.uk/itm/OA90-0A90-24mA-30V-GP-Signal-Diodes-Diode-50-Pack-NEW-/260504657489?pt=UK_BOI_Electrical_Components_Suppl ies_ET&hash=item3ca7499e51

50 for £6.50

As for matching, I would have thought just measure for the same forward voltage?

Richard.

(I think I am allowed to put an Ebay link in under this context, if not I am sure I will soon be told and I apologise in advance.)

audiomm · 6th Aug 2011, 10:15 pm

Quote:

Originally Posted by Dave UXB

Anyone know how to match a pair of germanium diodes for a RF bridge circuit please? In view of the scarcity of OA90/91, I plan on using 1N34A.

I use a Peak Component Analyser ( DCA55) - job done in seconds. I can heartily recommend you get one as they can also be used for measuring AND identifying all manner of semiconductors.

kalee20 · 6th Aug 2011, 11:09 pm

Bearing in mind that forward voltage, reverse leakage, and capacitance can all be an issue, I'd suggest match at near the operating frequency.

I matched a pair of germanium point-contact diodes for an FM discriminator recently, using a signal generator at 10.7MHz feeding the diode as a rectifier, and a 10kΩ and 0.1µF as load. Connecting a DC voltmeter across the load, I measured the voltage developed for each diode with unaltered sig gen output (set to give around 3V).

Out of 6 identical-looking diodes - thus presumeably from the same batch - I found there was a variation of about 50mV total between them. So for my discriminator, I used the pair that gave the closest voltage.

6th Aug 2011, 9:32 pm	#1
Dave UXB Retired Dormant Member Join Date: Dec 2008 Location: Staffordshire, UK. Posts: 116	Matching germanium diodes ? Anyone know how to match a pair of germanium diodes for a RF bridge circuit please? In view of the scarcity of OA90/91, I plan on using 1N34A.

6th Aug 2011, 9:46 pm	#2
Richard Heptode Join Date: Feb 2003 Location: Garnant, near Ammanford, South Wales, UK. Posts: 657	Re: Matching germanium diodes ? Hi There are OA90 and OA91 diodes on Ebay http://www.ebay.co.uk/itm/OA90-0A90-24mA-30V-GP-Signal-Diodes-Diode-50-Pack-NEW-/260504657489?pt=UK_BOI_Electrical_Components_Suppl ies_ET&hash=item3ca7499e51 50 for £6.50 As for matching, I would have thought just measure for the same forward voltage? Richard. (I think I am allowed to put an Ebay link in under this context, if not I am sure I will soon be told and I apologise in advance.) __________________ BVWS member.

6th Aug 2011, 11:09 pm	#4
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: Matching germanium diodes ? Bearing in mind that forward voltage, reverse leakage, and capacitance can all be an issue, I'd suggest match at near the operating frequency. I matched a pair of germanium point-contact diodes for an FM discriminator recently, using a signal generator at 10.7MHz feeding the diode as a rectifier, and a 10kΩ and 0.1µF as load. Connecting a DC voltmeter across the load, I measured the voltage developed for each diode with unaltered sig gen output (set to give around 3V). Out of 6 identical-looking diodes - thus presumeably from the same batch - I found there was a variation of about 50mV total between them. So for my discriminator, I used the pair that gave the closest voltage.