hybrid rectifier question

dr.strangelove3 · 30th September 2005, 05:05 PM

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?

NickC · 30th September 2005, 05:27 PM

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.
Hope this helps

dr.strangelove3 · 30th September 2005, 06:03 PM

Would it also reduce the switching noise of the ss bridge?

Tom Bavis · 30th September 2005, 06:42 PM

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...

amperex · 30th September 2005, 07:05 PM

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.

dr.strangelove3 · 3rd October 2005, 12:45 AM

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.

Geek · 3rd October 2005, 01:11 AM

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.

tubetvr · 3rd October 2005, 01:44 AM

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

Geek · 3rd October 2005, 05:01 AM

What a resource! Thanks Tubetvr

planet10 · 3rd October 2005, 06:18 AM

Just in case, here is what a hybrid (graetz) bridge looks like...

dave

30th September 2005, 07:05 PM	#5
amperex diyAudio Member Join Date: Feb 2005 Location: MI	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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30th September 2005, 05:27 PM	#2
NickC diyAudio Member Join Date: Dec 2001 Location: Earth	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. Hope this helps

30th September 2005, 06:03 PM	#3
dr.strangelove3 diyAudio Member Join Date: May 2004 Location: Leeuwarden	Would it also reduce the switching noise of the ss bridge?

30th September 2005, 06:42 PM	#4
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	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...

3rd October 2005, 12:45 AM	#6
dr.strangelove3 diyAudio Member Join Date: May 2004 Location: Leeuwarden	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.

3rd October 2005, 01:11 AM	#7
Geek diyAudio Member Join Date: Sep 2004	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.

3rd October 2005, 01:44 AM	#8
tubetvr diyAudio Member Join Date: Jan 2003 Location: Now back in Sweden	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

3rd October 2005, 05:01 AM	#9
Geek diyAudio Member Join Date: Sep 2004	What a resource! Thanks Tubetvr

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