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Recently I was talking to a friend about solid state rectifiers in tube amps. He told me that solid state rectifiers induces noise in the power supply, because the breakdown current of the silicon diodes, something like switching spikes.

Is this noise a really concern? How could I reduce, or even eliminate that problem?

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    \$\begingroup\$ There is irony in worrying about rectifier noise in a tube amp. :) \$\endgroup\$ – user3624 Aug 13 '13 at 13:40
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Diodes can be noisy when used as rectifiers due to reverse recovery induced spikes. Certain types of diodes perform better (schottky and so-called 'soft-recovery' diodes) or are essentially immune (silicon carbide) to this effect.

A well-designed circuit can address reverse recovery via the use of appropriate diodes (i.e schottkys and/or silicon carbide where appropriate) and by snubber networks, which absorb and dissipate the spike energy.

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  • \$\begingroup\$ True but to quote from your wiki reference "However, when the slew rate of the current is not so severe (e.g. Line frequency) the effect can be safely ignored." \$\endgroup\$ – JIm Dearden Aug 13 '13 at 12:55
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The V-I curve of a tube power rectifier has a much more rounded "knee" as compared to a solid-state rectifier. This tends to reduce the production of line-frequency harmonics that would fall in the audio band, allowing the designers of audio amplifiers to basically not worry too much about power supply rejection in their designs.

I don't know of any straightforward way to emulate this behavior in a solid-state replacement for a tube rectifier. Additional audio-band filtering in the power supply should help.

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Noise from solid state rectifiers in high speed switching power supply circuits do need to be addressed. However I can't see any merit how this would apply to an AC input 60Hz of audio amp. It is a slow sine wave and switches at o volts with slow slew rate. Tube rectifiers dissipate power due to there large forward voltage drop. They are unreliable and costly to replace. The power transformers have to compensate making them more costly. That's why they disappeared by the 60' even when silicon diodes were not that good. I don't recommend replacing tube rectifiers with solid state because the supply voltage will be higher and that may violate the maximum parameters of your amplifiers components. I stay away from any amp that uses tube rectifiers because it is just stupid.

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Diodes in audio amplifiers will generate noise than can be picked up in nearby AM radios. Not a problem that comes up much these days. Bypass each diode with a .01 uF X7R ceramic capacitor of the appropriate voltage.

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