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LM317 as CCS
LM317 as CCS
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Old 13th July 2019, 12:16 AM   #31
trobbins is offline trobbins  Australia
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decide67, you have measured the dc voltage of the cathode at idle, but I don't see any cathode voltage measurements with large signal - ie. to indicate if there is a dc bias movement as signal increase, and what is the AC voltage signal (ie. does the voltage across the 317 bottom out to less than about 3V, or increase to a level in excess of max rating).
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Old 13th July 2019, 07:00 AM   #32
6A3sUMMER is offline 6A3sUMMER  United States
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decide67, Be sure the bypass cap goes all the way from the 807 cathode to ground. It must go across both the LM317 and the sense resistor (LM317 and sense resistor are in series). If there are any other resistors in the 807 Cathode, you need to post the schematic. And if you are using any feedback to the 807 Cathode, you need to post the schematic. Again, the minimum working voltage across the LM317 plus its current sense resistor is 4V. What is the 807 screen connected to, a series resistor to B+ (how much resistance?), a regulated supply, UL tap, or what? Lets get this problem solved.
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Old 13th July 2019, 03:23 PM   #33
deicide67 is offline deicide67  United States
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I will try to doodle a schematic today at some point. I can say that adding a 270ohm “helper” resistor does get me a lot more clean power of approximately 5.3W at 1khz before clipping g and it has flattened out the response down low to similar to using a cathode resistor.
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Old 13th July 2019, 03:34 PM   #34
jackinnj is offline jackinnj  United States
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LM317 as CCS
If I recall, in later correspondence after Walt's "Current Sources 101" article, he determined that the LM317 is "noisy". It certainly is much noisier than a DMOS.
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Old 13th July 2019, 03:45 PM   #35
deicide67 is offline deicide67  United States
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It very well could be noisy, but if it is, it’s not anything of concern here. This amp is extremely quiet on the outputs.
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Old 14th July 2019, 03:49 AM   #36
deicide67 is offline deicide67  United States
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Thanks everyone for your input!

I now have the LM317 performing nearly equal to the simple cathode resistor. I have 273V on the plates with 288V B+, LM317 set to 52mA for just under 20W plate dissipation, 210V regulated G2 voltage. I get nearly 7W. I was getting a bit more but backed down the idle current to 52mA vs 56mA. The schematic has a bit of schade feedback and some global as well. I pulled the global, but adding it back leveled out the bass performance a bit.

Thanks again!
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