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Old 30th September 2005, 05:05 PM   #1
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Default hybrid rectifier question

I found this picture of this power supply. What would be the the advantage of placing a rectifying tube after a ss bridge rectifier like shown in the picture?
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Old 30th September 2005, 05:27 PM   #2
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You have a nice soft start circuit. Here the tube is just used for its turn on capabilities. Once the amp starts instead of B+ being at full potential it comes up as per normal tube rectifer being used. From what i see ss allows very high first capacitance value where else the tube will only see max of 47uf. Also in this case the tube is parallel for most normal rectifer tubes and allows double the amount of current flow.
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Old 30th September 2005, 06:03 PM   #3
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Would it also reduce the switching noise of the ss bridge?
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Old 30th September 2005, 06:42 PM   #4
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The first capacitor is connected BEFORE the vacuum diode, so it will have to be rated for peak of unloaded AC. Depending on warmup time, the output voltage won't rise nearly as high.

In this case, it would not reduce the switching noise. However, using its two diodes as half of the bridge WOULD reduce switching noise, as the SS and vacuum diodes are in series. But you'd be subject to the tube's peak current rating...

If I were building this circuit, I'd use the 6AU4 or 6DW4, not a WE tube made of unobtanium...
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Old 30th September 2005, 07:05 PM   #5
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Default Just wierd to me........

As stated, use two damper rectifier tubes such as the 6DE4 in one-half of the bridge to enjoy a quiet rectifier & delayed warm up of 20 to 25 seconds.

Who would want to find a somewhat rare 1.5KV rated relay anyways plus the delay circuit electronics.

60uF is plenty of capacitance & the damper diodes can handle that. That large capacitance of over 150uF is overkill for such a light current load. Plus, a the large in-rush current without a soft-start circuit at start-up & very high peak to average current causes strain on the high-voltage transformer.
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Old 3rd October 2005, 12:45 AM   #6
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Thanks for the replies.

As I understand from your replies, this design is not doing what I hoped it would do. I will look further into the options mentioned.
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Old 3rd October 2005, 01:11 AM   #7
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If you want to reduce or eliminate SS diode switching noise, bridge the pins with a 0.01uF ceramic disk of appropriate voltage value - 1KV for most purposes, 2KV for 500VAC+ secondary trannies.
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Old 3rd October 2005, 01:44 AM   #8
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For more advanced technique on how to remove ringing from SS rectifiers, see here http://www.hagtech.com/pdf/snubber.pdf. Check especially page 10 and 11 for differences using single caps and more advanced snubber networks.

I use series resistor cap combinations for all rectifiers in my OTL's with good results but I needed to do a lot of measurements to get the values right, I also use soft fast recovery diodes.

Regards Hans
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Old 3rd October 2005, 05:01 AM   #9
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What a resource! Thanks Tubetvr
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Old 3rd October 2005, 06:18 AM   #10
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Just in case, here is what a hybrid (graetz) bridge looks like...

dave
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