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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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2nd Sep 2014, 5:45 pm | #1 |
Heptode
Join Date: Dec 2011
Location: Mayabeque, Cuba
Posts: 617
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Doubts about pentode screen voltage
Hi all
I intend to use several 6J5P or 6J38P pentodes in future RF experiments, but I have a couple of doubts. My intention is to run the pentodes on 50 to 60 V DC, and to increase stability I thought to connect the screen to a regulated (via Zeners) voltage. 6J5P and 6J38P are equivalents of 6AH6 and 6BH6 respectively. http://www.radiomuseum.org/tubes/tube_6j5p.html http://www.radiomuseum.org/tubes/tube_6j38p.html First: Would that connection increase stability? (less hum, less noise.............nothing at all?) Second: What happen if the anode voltage falls bellow that on the screen? Thank you very much in advance.
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When electrons move, things happen. There's nothing you can do that can't be done. |
2nd Sep 2014, 6:15 pm | #2 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,082
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Re: Doubts about pentode screen voltage
If the anode voltage fell below the screen-grid, it should not matter. Bear in mind that output pentodes and beam tetrodes generally have their screen-grids tied to HT+, so about 250V or so, but the anode swings downward to 30V. Only when the anode voltage is so low that it goes round the 'knee' of the characteristic and current falls significantly, is there a problem.
With simple tetrodes, it's another matter and you get the negative resistance effect. |
3rd Sep 2014, 12:16 pm | #3 |
Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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Re: Doubts about pentode screen voltage
No need for Zeners, unless you are building a low power RF PA. Zeners can be noisy too.
Just use the usual resistor to supply rail, and capacitor to ground (or cathode). |