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Old 13th May 2021, 7:49 am   #23
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: AZ31 as rectifier for a stereo Mullard 3-3?

If the purpose of an amplifier is to modify the sound, like when a guitarist wants the HT to drop when he really starts expressing himself, then the saturation characteristics of valve rectifiers serves a purpose.

If the purpose of an amplifier is to faithfully magnify whatever is fed into its input, then there's nothing wrong with solid state rectification, and the amplifier designer would have happily used DC mains directly if it had been available and on the right voltage.

The only drawback is that the HT appears instantly, before the valves using said HT have warmed. So the voltage dropping resistors drop no volts for a while. You need to be sure voltage ratings are OK with this.

A guitar amplifier is part of the performance, and if the player likes valve rectifiers, so be it. If he pulls his HT down, it affects only his instrument and becomes part of its sound.

A reproduction amplifier has to handle all the instruments and vocalists at once. If one loud instrument pulls the HT down, then it mutilates the sounds from all the other instruments and vocalists. Intermodulation and cross-modulation just sound bad.

In the right places, silicon rectification is absolutely fine.

Taking the rectifier's heater load off of the mains transformer gives it an easier life.

David
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