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Valve questions from a total numpty |
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Fatmangolf
Moderator Group Joined: 23 Dec 2009 Location: Middlesbrough Status: Online Points: 8960 |
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Posted: 26 Jan 2016 at 6:35pm |
Sorry chaps.
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Jon
Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC. |
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Blame Jon |
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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morris_minor
Moderator Group Joined: 27 Mar 2012 Location: Surrey Status: Offline Points: 6015 |
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This thread has turned out to be more educational than I'd hoped . . .
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Bob
Majestic DAC/pre-amp Accession MC/Enigma, Accession MM, Reflex M, Elevator EXP, Era Gold V Solo ULDE, Novo, Lautus USB and digital, Libran balanced, CuSat50 2 x Proprius + Spatia/Spatia Links |
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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The "story" of the valve (tube) is related quite well here:
http://www.allaboutcircuits.com/textbook/semiconductors/chpt-13/the-triode/ http://www.allaboutcircuits.com/textbook/semiconductors/chpt-13/the-tetrode/ http://www.allaboutcircuits.com/textbook/semiconductors/chpt-13/beam-power-tubes/ http://www.allaboutcircuits.com/textbook/semiconductors/chpt-13/the-pentode/ keep clicking next page for more in-depth stuff. The very first page shows that valves have the same problems as transistors... capacitance. However, the Tetrode and Pentodes came into being to "solve" the problem whereas different techniques are used with transistors. Those techniques do not work for high powered high frequency circuits (like some radio transmitter power amps) where valves hold the monopoly. A good page for determining bias and gain of valves is: http://sound.westhost.com/valves/bias-gain.html |
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Yes, it has gotten out of hand a little and I must admit my sense of humour got the better of me, but the question was asked Now, cathode bypass caps are an interesting subject too: They're there to couple the cathode to ground for ac signals. At DC the resistor is required to lift the cathode voltage which makes the grid voltage negative with respect to the cathode. This biases the anode to somewhere between HT and ground. Just the right amount of voltage cathode to grid will bias the anode at half HT voltage allowing it to swing the full ac signal between HT and ground. If the bypass capacitor weren't there the gain would be reduced and would be the ratio of anode and cathode resistors (given a proper HT rail which many "new" designs don't), so for maximum gain from the valve, the cathode bypass capacitor is required. It needs to be large enough to do the lowest bass frequency expected and the formula F=1/2pi.RC is used for that. Rearrange to give C = 1/2pi.FR This particular bypass capacitor is where a lot of tweakers spend a lot of effort on. They seem to try lots of different types of capacitors and often bypass the bypass cap with all sorts of wonderful schemes. Instead, why not just put a high voltage GP 85 degree electrolytic there? 63V to 100V should work really well. Just ensure it's given sufficient ventilation to keep it cool. Beats Blackgates IMO! Edited by Graham Slee - 25 Jan 2016 at 7:07am |
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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Fatmangolf
Moderator Group Joined: 23 Dec 2009 Location: Middlesbrough Status: Online Points: 8960 |
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When I last logged in we were talking about anodes and cathodes. I come back and it's bovine gynaecology and proctology . Yes it's good to share experiences but I thought we'd be onto cathode bypass caps or something similar!
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Jon
Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC. |
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Martin1
Regular Joined: 19 Feb 2013 Location: Berks Status: Offline Points: 87 |
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Yes I do ,which shows both our ages . They still got my size wrong so was not exactly fool proof
still wondering why the nurse is smiling ,must be my natural innocence . Martin |
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Novo Solo SRGII PSU1 Cusat 50 Senn:250 Senn: 540II & Big Wish List
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