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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Why do you need DC heating ? posted by fatbottle on October 27, 2006 at 09:34:33:
I fully agree with fatbottle's points. DC heating is usually unnecessary and can actually be self-defeating if you don't guard against the introduction of noise in the heater supply. Don't forget that 60Hz is everywhere, not just in the heater circuit. It can be picked up by a sensitive input circuit from just about anywhere, including a poorly designed grounding scheme. If you do not already have star grounding I suggest you try it. Make sure there is only one connection to the chassis, preferably near the input jack.AC-bearing wiring in close proximity to signal-bearing conductors is another common cause of hum, which is why the power supply is usually located as far away from the input as possible and shielded wiring is frequently used for signal-bearing conductors of any great length. Using twisted pairs of AC conductors, including but not limited to heater wiring, is a good precaution to take.
Hum can sometimes be reduced by connecting a potentiometer (say 500 ohm) across the heater supply and connecting the slider of the pot to the "grounding" connection, which should probably be above ground potential DC-wise with a 10uF cap to actual ground. Adjust the slider to the position giving minimum hum.
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Follow Ups
- Re: Why do you need DC heating ? - Ray Moth 16:53:50 10/27/06 (2)
- Re: Why do you need DC heating ? - Jayme 15:20:59 10/28/06 (0)
- Re: Why do you need DC heating ? - fatbottle 03:08:37 10/28/06 (0)
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