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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 31st Jan 2016, 7:03 pm   #1
Tyso_Bl
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Default Burst Selenium rectifier substitute

Trying to work out what to replace this with, its a multi disc selenium jobbie, lookis like the encapsulation dissolved or otherwise failed from the spring tension.
Its a type FSY7093A , 120V rating. I can't find out anymore about its properties, such as its forward voltage drop, reverse leakage, forward resistance, etc.

Any thoughts? I'm going to do the obvious and try a silicon part, see what happens...
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Old 31st Jan 2016, 7:29 pm   #2
evingar
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Default Re: Burst Selenium rectifier substitute

If you are using silicon, stick a limiting resistor in series with it. Difficult to know what value to suggest without data for the selenium part - When I "Googled", the only reference I got was your post

Anyway, best to start with a high value and monitor the voltage rail it supplies- reduce the value of the resistor to suit.
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Old 31st Jan 2016, 7:38 pm   #3
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Default Re: Burst Selenium rectifier substitute

1N4007 and a 200 ohm resistor is the usual rule of thumb advice. If you use two diodes in series you reduce the voltage stress and will survive one failing short circuit. The resistor value isn't critical.
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Old 4th Feb 2016, 10:22 pm   #4
Tyso_Bl
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Default Re: Burst Selenium rectifier substitute

Thanks for the suggestions, I've studied the circuitry round this rectifier, and it purpose seems to be to prevent priming current leakage from the trigger of a cold cathode valve (fed via a 200 Meg resistor), in to a voltage divider network on the other side, while still allowing the voltage divider to influence the trigger voltage. The current is in the microamp region, any back leakage would totally negate the purpose of the rectifier / diode.

Slightly aside I've measured the capacitors in the unit as being leaky too, showing 15Meg for the worst ones. 0.1uF 350V.

On the verge of putting it away for another day.
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