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In Reply to: RE: 20uF is Not Too High posted by Triode_Kingdom on April 18, 2017 at 05:46:30
Does the ability to, apparently safely, exceed the data sheet specs by 100% have anything to do with current draw or other operating conditions? Or is this just an especially tough rectifier tube or ??? Do you think rectifier data sheets are deliberately ultra conservative in this regard?
Another rectifier, the 5AR4, has a max first cap rating of 60uF. Are there designs that safely use 120uF with this? The highest I've seen was with a Pilot 500 console amp that I restored (kind of mini version of the 232) which came with 80uF stock. I used a smaller cap when I rebuilt it.
I've always figured that going, maybe, 25% higher than a data sheet recommends would be about as far as any given rectifier should be pushed. That's just based on a vague philosophical belief not on analysis of technical data, though.
6X4 data sheets show 10uF as the typical value for a cap-input filter. To determine the actual maximum for a given application, it's necessary to use additional published data. The 6X4 is rated for a maximum transient peak plate current of 1.1A per plate. Charts published by the manufacturer(s) use this peak rating to show the required plate supply resistance in ohms VS the AC RMS voltage per plate, relative to a 10uF cap. Additional capacitance can be used as long as the peak plate current rating isn't exceeded. Simulation software is ideal for determining this.
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Boy, the cost of these things... I would not design an amp with more than 40mfd in the first stage. 120mfd is crazy! At that point, I'd seriously considered solid-state rectification.
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