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john dozier 20th January 2012 05:25 PM

Hexfred or SIC rectifiers in choke supplies
Are these really necessary in a choke type supply. We put some hexfreds into a choke type supply and really could hear no difference. It was a great deal of work and I would do the same on my amplifiers if there was a SQ improvement. What say you? Thanks and kindest regards John Dozier

DF96 20th January 2012 07:36 PM

It might depend on how far above the critical current you are. If only a little above, then the current at the low point of the voltage waveform will be quite small so not much charge storage in any diode. If well above, then current will be high at the point conduction switches from one diode to the other. If below the critical current then the circuit behaves more like a cap input supply so you get short sharp current pulses.

BTW by 'choke type supply' I assume you mean choke input PSU

john dozier 20th January 2012 07:44 PM

Yes, it is a choke input supply. 440ufd then the choke(unknown value) then another 440ufd. Quite a hefty choke though for a hefty amp-8 el34s in each monoblock. ASL Monsoons. thanks I do not mind paying for improvements in SQ but perhaps high speed an soft diodes have become a flavor of the month item and may not be so useful in tube equipment as they are in digital and SS.

john dozier 20th January 2012 07:46 PM

My knowledge in this area is forty years old and I do not know to separte the wheat from the chaff. Thanks

DF96 20th January 2012 07:49 PM


440ufd then the choke(unknown value) then another 440ufd.
That sounds like a description of a cap input supply. Do the rectifiers feed a cap or a choke?

john dozier 20th January 2012 08:38 PM

They feed the first bank of caps. Regards-it is a cap input supply-I just use the generic choke supply for any PS that has a choke.

DF96 20th January 2012 08:51 PM

In that case ignore what I said, as it only applies to choke input supplies.

The effect of different diodes in a cap input supply will depend to some extent on wiring and grounding details; if done correctly the diodes could have less effect.

Sch3mat1c 21st January 2012 06:54 PM

They are not necessary in any supply. Save your money and get some 1N4007's. If you hear buzzing in your amp, put in a few caps across the diodes. The same is true of any other type of diode, if you are getting noise, you still need caps.

I can assure you, there is nothing special or magical about any semiconductor diode available on the market. There is no double-blind perceptible difference in any aspect of the amplifier (from gain or distortion, to subjective terms like "presence" and so on) in using them, as long as switching noise is minimized, which is a precaution required with any diode type, or filter type (cap or choke input).

Now... if you aren't interested in double-blind-perceptible differences, that is, you literally want to spend more money on the amplifier to make it look or feel pretty, please DO spend the money to purchase a beautiful copper chassis, or a lacquered wood box, or spend extra time on the layout. Beautiful tubes deserve beautiful settings. You will get much more enjoyment out of these aspects than out of knowing some marginally different diode is pumping away inside.


jcx 21st January 2012 07:11 PM

some indirect interference may be hard to AB/X - but good engineering does design, test for EMI immunity

EVA has some convincing meaurements of rectifier revese recovery currents

untreated they are an EMI source inside your amp enclosure

properly sized RC "snubber" can be more effective than just caps - but either can cut the noise radiation considerably for even 1N00x class diodes

kevinkr 21st January 2012 10:52 PM

UF4007 diodes are cheap, and their fast recovery characteristics help reduce EMI.. Anything beyond this is probably at the point of diminishing returns. FWIW I can't hear any difference between diodes in a correctly designed amplifier. (Sometimes I can measure a little more noise, quickly resolved as others have commented by adding caps or snubbers across the rectifier.)

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