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Old 5th May 2010, 08:56 AM   #1
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Default Misunderstand of sijosae schematic

Why need 2 LM317 to operate one filament? urgent!
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Old 5th May 2010, 09:55 AM   #2
SY is offline SY  United States
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Schematic?
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Old 5th May 2010, 10:16 AM   #3
Arnulf is offline Arnulf  Europe
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Quote:
Originally Posted by crashman View Post
Why need 2 LM317 to operate one filament? urgent!
Because the author drew his schematic this way ? Each regulator delivers cca. 145 mA, tube requires 300 mA to operate. Perhaps he wanted to spread the heat around ... who knows. With decent heatsink you can easily use just one LM317 (and change value of 20R and 15R resistors, of course, to get parallel resistance of cca. 4.16R).
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Old 5th May 2010, 12:49 PM   #4
Yvesm is offline Yvesm  France
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My first impression was "will never flight" !
But, at a second look it seems to me that each LM317 is used as pull down for the IRF610 source followers.
Don't be confused by the "+Bat-1" and "+Bat-2" labels which are indeed the anode connections to each active load (2SK30) wich each drive an IRF610.
If so, each source follower draw near 150 mA.

My two pence.

Yves.
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Old 5th May 2010, 12:55 PM   #5
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Thanks for the input guys, but the measurement between filament and the ground is more than 20 volts.
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Old 5th May 2010, 12:58 PM   #6
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thanks guys , but the measurement between the filament to the ground is more than 20 volt. do you guys get this value?
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Old 5th May 2010, 02:15 PM   #7
Arnulf is offline Arnulf  Europe
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Put tube into socket and the readings will go down to 6.3V.

Measuring open CCS will give, well, what any self-respecting CCS should give into infinite impedance - infinite voltage, supply permitting
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Old 5th May 2010, 04:44 PM   #8
kevinkr is offline kevinkr  United States
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It appears that those ccs both control the current through the output devices on each channel and each one also provides half the filament power. (current sources sum directly [Norton]) It is actually rather clever and obviates the need for a separate filament supply and also reduces the dissipation across each LM317 as the voltage across them is reduced by the amount of the filament voltage.

This works well because the swings required at the output are small as compared to the available supply voltage, the ability to swing in the negative direction is compromised by the voltage drop of the filament.
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Old 5th May 2010, 04:52 PM   #9
Yvesm is offline Yvesm  France
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So, you confirm my guesses
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Old 5th May 2010, 10:21 PM   #10
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I have a new problem. the LM317 is hotter than the other one. lol
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