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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: RE: The Cap is not Superflous posted by Alex Kitic on October 27, 2014 at 12:11:46:
"From my experience, there is no relevant noise to start with - which might have been contributed by the zener diode."
Yes, it may very well be that noise contributed by the Zener is insignificant in the larger picture.
"Whoever wants to try it for himself, should do it, and let us know :)"
This is a place for measurement first, listening later. The question is whether Zener noise contributes to system idle noise at the output of the amplifier. Whether a particular owner can hear it with a given system is irrelevant to optimizing the design of the amplifier. A FFT (hardware or software) is required to analyze this issue accurately.
Also, just to address one other point you raised to support the claim that the cap is superflous...
"Adding a 10uF cap from g2 to ground will most probably create an inadequate filtering cell."
The 6BQ5 G2 draws approximately 6mA. That current through the Zener, along with a 21V drop, equates to an effective impedance of 3,500 ohms. Under these conditions, a 10uF cap at the screen will decouple the grid sufficiently to create more than 45 dB attenuation at 1K. Whether this is effective at the output depends on many factors, including the AC impedance of the primary B+ supply. At the very least, I would consider this a good safeguard against degradation (likely in the form of distortion) by a screen that that might not otherwise be sufficiently regulated.
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Follow Ups
- RE: The Cap is not Superflous - Triode_Kingdom 13:25:22 10/27/14 (0)
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