mjlewis22 Posted August 24, 2010 Share Posted August 24, 2010 Can someone explain how to identify the plate resistor (or Pin 1/6) and properly drain the caps to avoid killing oneself? I've already made up an alligator clip w/ resistor in it for this purpose, I just need to know how to find the plate resistor, drain the caps, and then check them to make sure they have been drained to a safe level. I am working with the PCB in place, so I cannot access the underside of the caps. I can access the tube pin solder joints though, as they are on "top" of the board. Thanks, --ML Link to comment Share on other sites More sharing options...
fuse Posted August 24, 2010 Share Posted August 24, 2010 I do not think you are in much risk of being killed..... What amp is this for....a Valve Jr.....? You can ground the positive side of the large filter caps, and you can ground Pin 1 and Pin 6 of the preamp tube, and you can ground Pin 7 and Pin 9 of the EL84....assuming this is a VJr. All the common sense stuff applies....power cord un-plugged, don't grab stuff with both hands, etc. etc. To check, you just place the red lead of your meter on the filter caps and the black lead to ground. 2 or 3 residual volts is nothing to worry about. Does that make sense? Link to comment Share on other sites More sharing options...
mjlewis22 Posted August 24, 2010 Author Share Posted August 24, 2010 I was able to determine that the plate resistor for the first preamp tube was R4, as per the schematic of the BC30. So, I did this: The alligator clip and the red clip are connected by a 5.6k resistor. Good to go now? Link to comment Share on other sites More sharing options...
fuse Posted August 25, 2010 Share Posted August 25, 2010 Can you post a copy of the schematic....? You need to check the B+ on all the tubes, not just V1. If it is PCB and hard to deal with, just ground Pin 1 and Pin 6 on the pre tubes and the screens and plates of the power tubes. I am not familiar with the BC30, so I do not know what power tubes it uses; but you get the gist of what I am saying. Then just check a few of those point with your meter. Your caps are probably drained by now anyway. But that is not the point of your post..... Link to comment Share on other sites More sharing options...
Cheeks Posted August 25, 2010 Share Posted August 25, 2010 The bigger the capacitance, the longer the TIME it will take to drain the residual charge. So, for some filter caps, you may have to wait a half minute... before disconnecting the temporary grounding strap you made-up... CHEEKS Link to comment Share on other sites More sharing options...
jefrs Posted November 23, 2010 Share Posted November 23, 2010 The common or garden voltmeter is almost the ideal too for draining the HT off: it hath resistance and displays when it's done. BTW regarding "I do not think you are in much risk of being killed....." whilst connecting yourself across the mains or the HT of an amp /can/ kill you, it usually just hurts a lot. Link to comment Share on other sites More sharing options...
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