Wilkinson SR-8 SS Rect

[kd1nw]

Hi All,

I have some Wilkinson SR-8 ss rectifiers that I was thinking of using in a globe champ 300. They have neon lamps, one for each diode. What are these lamps for? Are they indicators to show that the diode is still good?  The stack is 8 1N4007, equalized with .01uf 1kV and 430kOhm, one end of the lamps is floating the other end connects to the stack through a meg ohm resistor.

Thanks 73
Kevin - KD1NW

[w4bfs]

interesting  ... are you sure that one end of each neon bulb is not connectecd at all ?

[Pete, WA2CWA]

You can see one bare wire from each neon going to a terminal (one side of diode). Other bare wire looks to be connected in mid air to a 1 Meg resistor and other end of the 1 Meg resistor going to another terminal (other side of diode). Maybe in its original application, the neons were used to indicate an open diode.

[kd1nw]

Hi, yep they are all disconnected. I just took a close look and they used to be connected. someone cut them. I checked the ones on the SR-12 and they are connected. Thanks guys, I guess I can reconnect them, seems like having a failure indicator would be a good thing to have.

[w8khk]

It appears to me that the neon lights should all be illuminated when the rectifier is working properly.

Assume, for example, a 1000 volt DC supply, with a center-tapped full wave  rectifier.  When all the diodes are conducting, there is less than a volt across each device.  But, on the opposite half-cycle, when the diodes are reverse-biased, there will typically be a peak of 2000 volts across the eight diodes in the string, 1000 from the capacitor, and 1000 from the peak voltage from the transformer.  When using the diode string with higher voltage supplies, the neon bulb will regulate its voltage and the excess voltage will appear across the 100 kohm resistor.

If all the diodes are sharing, approximately equally, the 2000 volts, then each diode will have around 250 volts across its terminals.  The neon bulb, with the 100 kohm series resistor, should ignite and glow rather brightly.  If any of the diodes short, or if the capacitor across the diode shorts, then that neon bulb will not illuminate, indicating the need for service.

It is usually not necessary to use equalizing resistors and capacitors across diodes of current manufacture, but years ago it was recommended due to manufacturing tolerances, such that each diode would receive its rightful share of reverse voltage.  With the neon indicators on your diode strings, you will know when one of the diodes fails, and can replace it before the others fail due to excessive reverse voltage.

[kd1nw]

Thanks for the great explanation Rick