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-   -   Diodes in a Graetz Hybrid (http://www.diyaudio.com/forums/tubes-valves/208717-diodes-graetz-hybrid.html)

Jeffrey Davison 13th March 2012 05:31 PM

Diodes in a Graetz Hybrid
 
IXYS HiPerFreds, Fairchild Stealths, Cree SIC Shottkies.

I know the technical differences, but.....

What are the "sonic" differences when used in a Greatz Hybrid bridge?

Since the tube is the "slowest" recovery element of the equation, and the one that gives the bridge it's basic sonic signiture, does the type of diodes mentioned above really make a substantial audible difference?

Say the tube will be a 5U4G and the B+ around 490 VDC after the filter.


JD

Osvaldo de Banfield 13th March 2012 05:56 PM

I believe that is very stupid to mix tubes and semiconductors in the same circuit. Use Si diodes OR tube in full wave.

kevinkr 13th March 2012 06:06 PM

Quote:

Originally Posted by Osvaldo de Banfield (Post 2944454)
I believe that is very stupid to mix tubes and semiconductors in the same circuit. Use Si diodes OR tube in full wave.

It's not IMHO, works fine and in the case of the 5AR4/6V4/6CA4 provides useful warm up delay that you don't get with a solid state bridge without significant additional complexity.

The 5AR4 is also noted for hot start arcing issues, particularly current production and placing a UF4007 in series with each plate completely prevents this issue and does not otherwise alter rectifier performance wrt voltage regulation, warm up delay or EMI.

I would not spend the money on exotic solid state rectifiers for use in the Graetz bridge, nor probably anywhere else for that matter because I can't hear any difference in a properly designed circuit. UF series rectifiers are cheap and help wrt to EMI, anything beyond that in low current high voltage supplies may be overkill. (JMO)

Jeffrey Davison 13th March 2012 06:32 PM

good opinionated debate on the merits or not of a hybrid rectifier, methinks that's off topic from the start gents. What are the sonic differences between the diodes I mentioned?
Any ears here ?

JD

kevinkr 13th March 2012 06:49 PM

As I stated in my last post I have not been able to demonstrate any audible difference in tube gear between any solid state rectifiers in a properly implemented design. IMHO it's an audiophile fashion statement. I've wasted money on hexfreds because of the hype and won't do that again. Last time I checked I had a fairly good pair of ears. :D

Seriously though you should just go out and try them - nothing like direct experience, perhaps you will not be as disappointed as I was..

In the Graetz bridge the type of SS diodes used make no audible difference that I can discern.

Osvaldo de Banfield 13th March 2012 06:54 PM

Quote:

Originally Posted by Jeffrey Davison (Post 2944499)
What are the sonic differences between the diodes I mentioned?

JD

I donīt know. One time power is rectified, and filtered, I canīt understand which may be the difference between SS rectifiers and VT ones. I found in a regenerative receiver I made 2 years ago, first with SS rectifiers, and latter with a 6X4 is the time takes to get +B at the bus. I rewind the Xformer to get same voltage with both rectifiers, and no audible difference, except for the level of ripple (Diodes were doubling in half wave, tube is full wave). And, the change was in order to get this regen all tubes. But, again, I couldīt find audible differences.


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