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In Reply to: RE: RH84 : LM317 CCS for EL84 ... posted by deathtube 667 on January 20, 2015 at 05:25:49
Did you try it again after everything cooled down? The LM317 is supposed to be thermally protected. I have to say, I'm not a fan of connecting a device like the 317 directly to the cathode.
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I added a small bolt & screw to the output tap on the LM317 for heatsinking and the amp seems to be playing normally again.
Normally, I put such circuits on small perfboards with heatsinks and not directly on the tube socket.
I have installed the LM317 on numerous amplifiers including 3 RH types. All were installed directly on the cathode pin of the tube socket with seemingly no problems. The bias was stable in all the amps and so far no problems. I don't have instrumentation to measure its effect but to my ears, the sound is improved especially in terms of dynamics and bass. regards, Dak
I needed to put the LM317 on a tag strip away from the tube socket, then put the cap on the socket to get it to regulate the current properly in my test amp when I raised the B+ up to 300VDC.
Never tried LM317 as a CCS before, so I was on the low end of the learning curve in this case.
The only CCS I have used before were for plate loading of driver stage and finals with BJT or mosfet devices. Never bypassed any of those.
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