1 00:00:15,650 --> 00:00:21,610 >> The purpose of this video is to dispel some myths about discharging a tube amplifier. 2 00:00:21,610 --> 00:00:25,305 I am using a vendor blues junior here as an example, 3 00:00:25,305 --> 00:00:28,575 but it applies to any other tube amplifier. 4 00:00:28,575 --> 00:00:31,125 As you can see, I've got a volt meter, 5 00:00:31,125 --> 00:00:35,145 hooked up to the main power supply filter capacitor, 6 00:00:35,145 --> 00:00:38,190 and it's measuring four volts right now, 7 00:00:38,190 --> 00:00:42,080 which is just a chemical residue in the electrolytic capacitor, 8 00:00:42,080 --> 00:00:43,550 it doesn't really mean anything, 9 00:00:43,550 --> 00:00:46,640 it's just a byproduct, 10 00:00:46,640 --> 00:00:48,455 not at all important. 11 00:00:48,455 --> 00:00:52,800 I'm going to turn the amplifier on and then turn it off quickly. 12 00:00:53,660 --> 00:00:57,800 Now, you see that it's going down and went up to 13 00:00:57,800 --> 00:01:01,850 about 330 volts and it slowly going down 266, 14 00:01:01,850 --> 00:01:07,580 265 and it's discharging slowly just leaking 15 00:01:07,580 --> 00:01:10,160 through various components inside the amp and 16 00:01:10,160 --> 00:01:13,880 natural leaked down that you get with electrolytic capacitors, 17 00:01:13,880 --> 00:01:17,390 but that's more than enough voltage to knock you on your tail, 18 00:01:17,390 --> 00:01:19,820 so you don't want to mess around with that. 19 00:01:19,820 --> 00:01:26,480 Now, one way to discharge a cold amplifier like this is with 20 00:01:26,480 --> 00:01:35,625 a simple jumper wire with a 10,000 ohm resistor 10K resistor held in one clip. 21 00:01:35,625 --> 00:01:40,570 If I touch that, actually anywhere around here, 22 00:01:40,790 --> 00:01:49,680 it'll take the voltage down rather quickly, 8460, 2216, 1812, 23 00:01:49,680 --> 00:01:53,870 anywhere in the power supply will take it down. 24 00:01:53,870 --> 00:01:56,610 Now we're down to two, one volt. 25 00:01:57,640 --> 00:02:04,985 So, that's a very safe and easy way to discharge any amplifier. 26 00:02:04,985 --> 00:02:07,700 The 10K resistor only prevents sparking, 27 00:02:07,700 --> 00:02:10,560 I could touch it directly but I would get an arc, 28 00:02:10,560 --> 00:02:14,915 the 10K resistor slows down the discharge and makes it easy. 29 00:02:14,915 --> 00:02:16,895 Now, let's do the same thing again, 30 00:02:16,895 --> 00:02:20,800 we'll bring the amp up to full operating voltage, 31 00:02:20,800 --> 00:02:22,995 which is in this case, 32 00:02:22,995 --> 00:02:27,400 we see 347 volts, 348, 33 00:02:27,560 --> 00:02:31,720 and as the two tubes warm up, 34 00:02:32,450 --> 00:02:35,840 you'll see that the amp will actually drop in 35 00:02:35,840 --> 00:02:39,480 voltage because the tubes will start conducting. 36 00:02:39,550 --> 00:02:46,220 Now it's down to 333, 334, 330. 37 00:02:46,220 --> 00:02:49,700 So this is a normal voltage that you would see in a blues 38 00:02:49,700 --> 00:02:53,975 junior with normal operating conditions. 39 00:02:53,975 --> 00:02:58,620 Now, you can play through the amp, it's live. 40 00:03:00,080 --> 00:03:02,685 Now, if we just turn it off, 41 00:03:02,685 --> 00:03:06,950 remember we turned it off before when the amp was cold and nothing happened. 42 00:03:06,950 --> 00:03:12,590 Now, I'm going to turn it off and watch how quickly the voltage goes down, 50, 42, 43 00:03:12,590 --> 00:03:16,875 26, 16, faster than it did through the 10K resistor, 44 00:03:16,875 --> 00:03:19,335 three volts, two volts. 45 00:03:19,335 --> 00:03:24,530 Why? Because it's conducting through the ELAD force primarily and the other tubes, 46 00:03:24,530 --> 00:03:29,345 but these guys are always using a lot of current all the time. 47 00:03:29,345 --> 00:03:35,635 So, simply turning off a warm amplifier is all you have to do to discharge it. 48 00:03:35,635 --> 00:03:38,010 So, now we can strum it, 49 00:03:38,010 --> 00:03:39,795 nothing is coming through the amp, 50 00:03:39,795 --> 00:03:41,850 and this is ice cold, 51 00:03:41,850 --> 00:03:44,005 I can touch it with confidence, 52 00:03:44,005 --> 00:03:47,875 know that I'm not going to get knocked on my tail or anything like that. 53 00:03:47,875 --> 00:03:55,775 So, what about the old myth of having to strum the guitar while you're discharging? 54 00:03:55,775 --> 00:04:00,420 Let's take a look at that, we'll bring it back up to operating voltage again. 55 00:04:05,450 --> 00:04:09,970 So, we're stable at around 334 volts, 56 00:04:11,750 --> 00:04:14,115 and we have a normal sound, 57 00:04:14,115 --> 00:04:17,139 and now we'll strum while we're discharging, 58 00:04:19,550 --> 00:04:22,870 the powerful E chord there, 59 00:04:24,410 --> 00:04:31,395 and you notice that it discharged in exactly the same way as it did when we didn't strum. 60 00:04:31,395 --> 00:04:34,450 There is no reason to actually strum the guitar, 61 00:04:34,450 --> 00:04:38,045 that's just one of those internet myths that gets perpetuated. 62 00:04:38,045 --> 00:04:41,840 The only thing that the strumming does is 63 00:04:41,840 --> 00:04:46,910 confirm that all of the current is gone from the tubes, 64 00:04:46,910 --> 00:04:48,005 but it can be deceptive, 65 00:04:48,005 --> 00:04:53,645 if you had turned the amplifier on and off quickly and these were cold tubes, 66 00:04:53,645 --> 00:04:58,120 it would hold a charge and it wouldn't play when you strummed it. 67 00:04:58,120 --> 00:05:04,025 So, the safest thing to do is always to bring the amp up to full operating temperature, 68 00:05:04,025 --> 00:05:07,190 so you can play through it and simply turn it off, 69 00:05:07,190 --> 00:05:09,635 that will always discharge it all the way down. 70 00:05:09,635 --> 00:05:10,970 Don't put it in standby, 71 00:05:10,970 --> 00:05:12,785 don't do anything else with it, 72 00:05:12,785 --> 00:05:15,274 and you can play if you want to confirm, 73 00:05:15,274 --> 00:05:16,850 as the sound fades out, 74 00:05:16,850 --> 00:05:22,050 you know that it's being discharged and that's all there is to it.