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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 12th May 2021, 12:42 pm   #21
qualityten
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Default Re: AZ31 as rectifier for a stereo Mullard 3-3?

Thanks for this Trevor. Thinking this through for myself, I have gone ahead and used the 6.3V-0 winding for the EZ81 heater and the 3.15-3.15 winding for the heaters of other valves. I've not yet finished wiring it up, so I thought I'd wait till this was done before reporting on my results.

If I have one point where all the transformer grounds and the power socket earth are grounded to the chassis, should I still have a ground point near the inputs? Or should I ground everything, except the IEC socket earth, near one input. Reading your comment, I think the latter!
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Old 13th May 2021, 5:04 am   #22
Diabolical Artificer
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Default Re: AZ31 as rectifier for a stereo Mullard 3-3?

Chassis ground like 0v & screen from tfmr all to one point near C1 or 1st big filter cap,then a bus bar goes to that too. Next in this order onto the busbar, OP stage, phase splitter if any, then IP stage & IP from RCA in. the idea being to keep high current grounds away from sensitive IP stages.

Andy
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Old 13th May 2021, 7:49 am   #23
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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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Old 13th May 2021, 8:00 am   #24
GrimJosef
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Default Re: AZ31 as rectifier for a stereo Mullard 3-3?

Quote:
Originally Posted by Radio Wrangler View Post
... 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 ...
Did you mean "If the only purpose ..." ?

Cheers,

GJ
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