Selenium rectifier replacement Blaupunkt Car radio - UK Vintage Radio Repair and Restoration Discussion Forum

sctbrd01 · 27th Jan 2018, 4:24 pm

Looking at the thread for Blaupunkt Frankfurt X:-

https://www.vintage-radio.net/forum/...d.php?t=116715

There is a statement:

All AEG selenium rectifiers are suspect. I replace with 2 x 1N4003 diodes in series and reset the bias according to the service sheet. There is usually enough range of adjustment to accommodate the differing forward voltage drop - otherwise fit one Ge diode and one Si.

Is there a more direct replacement for X650- E30 C60-1 (SEL 0868/15x marking)?
Why would one use 2 diodes in series? Wouldnt they allow the same amount of current as a single?

https://www.vintage-radio.net/forum/...9&d=1432937581

I am looking for something that will replace the Selenium rectifier (diode), and don't have the expertise to choose correctly using data sheets or specs.

Thanks!

Station X · 27th Jan 2018, 6:03 pm

The selenium rectifier is being used to derive a bias voltage, which depends on its forward volt drop.

Semi-conductor diodes have a lower forward volt, so you'll need to use two in series.

Boater Sam · 28th Jan 2018, 7:41 am

Further.
Forward volts drop - For silicon diodes, the built-in potential is approximately 0.7 V, 0.3 V for germanium, and 0.2 V for Schottky.
The selenium rectifier has a volts drop of 1v per plate/junction so overall volts drop depends on the working voltage of the stack. Max reverse voltage is around 25v per plate so a mains stack would have at least 10 plates, normally 12 to 15 and drop 10 to 15 volts when new. This is why it is important to use a series resistor when replacing them as HT rectifiers with semiconductor diodes.
The forward voltage drop tends to increase with age.

Craig Sawyers · 28th Jan 2018, 9:06 am

All the above from Boater Sam.

However, GD rectifiers http://www.gdrectifiers.co.uk/ still make them, and do one off custom work http://www.gdrectifiers.co.uk/produc...um_rectifiers/

They use aluminium plates, which have long life and don't suffer problems with rusting and associated degradation that old rectifiers do.

They made replica rectifiers for the Lorenz SZ42 cipher machine I restored at Bletchley Park; they even painted them the same red colour as the originals.

27th Jan 2018, 4:24 pm	#1
sctbrd01 Retired Dormant Member Join Date: May 2016 Location: Manitowoc, Wisconsin, USA. Posts: 3	Selenium rectifier replacement Blaupunkt Car radio Looking at the thread for Blaupunkt Frankfurt X:- https://www.vintage-radio.net/forum/...d.php?t=116715 There is a statement: All AEG selenium rectifiers are suspect. I replace with 2 x 1N4003 diodes in series and reset the bias according to the service sheet. There is usually enough range of adjustment to accommodate the differing forward voltage drop - otherwise fit one Ge diode and one Si. Is there a more direct replacement for X650- E30 C60-1 (SEL 0868/15x marking)? Why would one use 2 diodes in series? Wouldnt they allow the same amount of current as a single? https://www.vintage-radio.net/forum/...9&d=1432937581 I am looking for something that will replace the Selenium rectifier (diode), and don't have the expertise to choose correctly using data sheets or specs. Thanks!

27th Jan 2018, 6:03 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Selenium rectifier replacement Blaupunkt Car radio The selenium rectifier is being used to derive a bias voltage, which depends on its forward volt drop. Semi-conductor diodes have a lower forward volt, so you'll need to use two in series. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

28th Jan 2018, 7:41 am	#3
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Selenium rectifier replacement Blaupunkt Car radio Further. Forward volts drop - For silicon diodes, the built-in potential is approximately 0.7 V, 0.3 V for germanium, and 0.2 V for Schottky. The selenium rectifier has a volts drop of 1v per plate/junction so overall volts drop depends on the working voltage of the stack. Max reverse voltage is around 25v per plate so a mains stack would have at least 10 plates, normally 12 to 15 and drop 10 to 15 volts when new. This is why it is important to use a series resistor when replacing them as HT rectifiers with semiconductor diodes. The forward voltage drop tends to increase with age.

28th Jan 2018, 9:06 am	#4
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,984	Re: Selenium rectifier replacement Blaupunkt Car radio All the above from Boater Sam. However, GD rectifiers http://www.gdrectifiers.co.uk/ still make them, and do one off custom work http://www.gdrectifiers.co.uk/produc...um_rectifiers/ They use aluminium plates, which have long life and don't suffer problems with rusting and associated degradation that old rectifiers do. They made replica rectifiers for the Lorenz SZ42 cipher machine I restored at Bletchley Park; they even painted them the same red colour as the originals.