One B+ for the both driver and output tube if they are identical? - diyAudio
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Old 23rd August 2006, 10:24 PM   #1
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Default One B+ for the both driver and output tube if they are identical?

Is there any disadvantage to feed a driver and an output tube from the same B+ PSU if the driver and the output tubes are the same DHT connected through an interstage transformer and the PSU has enough current in reserve?

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Old 24th August 2006, 05:20 AM   #2
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Probably no disadvantage, even if you don't decouple the HT between the stages. However, with more then two stages there is a risk of positive feedback between the 1st and 3rd stages, which can lead to LF instability (motorboating). It's normal practice to decouple the HT for every stage.
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Old 24th August 2006, 06:50 AM   #3
zobsky is offline zobsky  India
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kinda unrelated, but I'm assuming you an RC decoupling scheme is typically used. What kind of R and C values should one aim for (assuming there is no need to burn off voltage)?
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Old 24th August 2006, 10:41 AM   #4
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I seem to remember reading that capacitance in uF x resistance in ohms/1,000,000 should be 0.1 or greater, for good decoupling.

So, from this rule of thumb, if you want a small voltage drop and use e.g. a 470 ohms resistor, the minimum capacitance you need = 1,000,000x 0.1/470 = approx. 220uF.
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Old 26th August 2006, 12:01 AM   #5
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Default Thank you for the responses!

Thank you for the responses!
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Old 26th August 2006, 02:54 AM   #6
zobsky is offline zobsky  India
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thanks from me too
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