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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: original supply question for you.??????? posted by John PA on November 29, 2000 at 08:41:18:
Hmm, something is not right here. It sounds as if the original supply in the Cary is a cap-input supply, with the first element after the rectifier being a large capacitor. Cary is right that inserting a choke after the cap, assuming its DC resistance is not huge, will result in a relatively small voltage drop, or no drop at all if it replaces what was already there, ie, a resistor of some value equal to or greater than the DC resistance of the choke that you want to use. The choke is then followed by another capacitor, and you have a pi filter.If a choke is the first element after the rectifier, however, you have something totally different, and the voltage change is very large, much larger than what you would calculate just using the DC resistance of the choke and the current draw of the amp.
As an example, consider a typical 750vct transformer in a tube power amp. Ignoring the resistances of the rectifier and the choke, the voltage of the supply in a cap-input supply (pi filter) would be roughly .7 times the 750 volts, or about 525 volts. Change the supply so that a choke is the first element, however, and your choke-input supply voltage is only about .45 times those 750 volts, or about 338 volts. One famously enthusiastic mailing list denizen once remarked about the huge difference in sound that resulted from deleting "just one capacitor" in his amp ... the first cap in a pi filter.
If you can, just measure the resistor that follows that first cap, get a list of the Hammond chokes, and pick one that is rated for your current demand and is of the same or similar resistance. Then, if you want a nice upgrade, since you're now going to get better hum filtering, you can reduce the size of that first cap, substituting something that's sonically more benign, and reducing the stress on that rectifier tube. Just a thought ... - Pat
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Follow Ups
- Re: original supply question for you.??????? - tubesguy 12:16:14 11/29/00 (0)
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