WEBVTT 00:00:15.650 --> 00:00:21.610 >> The purpose of this video is to dispel some myths about discharging a tube amplifier. 00:00:21.610 --> 00:00:25.305 I am using a vendor blues junior here as an example, 00:00:25.305 --> 00:00:28.575 but it applies to any other tube amplifier. 00:00:28.575 --> 00:00:31.125 As you can see, I've got a volt meter, 00:00:31.125 --> 00:00:35.145 hooked up to the main power supply filter capacitor, 00:00:35.145 --> 00:00:38.190 and it's measuring four volts right now, 00:00:38.190 --> 00:00:42.080 which is just a chemical residue in the electrolytic capacitor, 00:00:42.080 --> 00:00:43.550 it doesn't really mean anything, 00:00:43.550 --> 00:00:46.640 it's just a byproduct, 00:00:46.640 --> 00:00:48.455 not at all important. 00:00:48.455 --> 00:00:52.800 I'm going to turn the amplifier on and then turn it off quickly. 00:00:53.660 --> 00:00:57.800 Now, you see that it's going down and went up to 00:00:57.800 --> 00:01:01.850 about 330 volts and it slowly going down 266, 00:01:01.850 --> 00:01:07.580 265 and it's discharging slowly just leaking 00:01:07.580 --> 00:01:10.160 through various components inside the amp and 00:01:10.160 --> 00:01:13.880 natural leaked down that you get with electrolytic capacitors, 00:01:13.880 --> 00:01:17.390 but that's more than enough voltage to knock you on your tail, 00:01:17.390 --> 00:01:19.820 so you don't want to mess around with that. 00:01:19.820 --> 00:01:26.480 Now, one way to discharge a cold amplifier like this is with 00:01:26.480 --> 00:01:35.625 a simple jumper wire with a 10,000 ohm resistor 10K resistor held in one clip. 00:01:35.625 --> 00:01:40.570 If I touch that, actually anywhere around here, 00:01:40.790 --> 00:01:49.680 it'll take the voltage down rather quickly, 8460, 2216, 1812, 00:01:49.680 --> 00:01:53.870 anywhere in the power supply will take it down. 00:01:53.870 --> 00:01:56.610 Now we're down to two, one volt. 00:01:57.640 --> 00:02:04.985 So, that's a very safe and easy way to discharge any amplifier. 00:02:04.985 --> 00:02:07.700 The 10K resistor only prevents sparking, 00:02:07.700 --> 00:02:10.560 I could touch it directly but I would get an arc, 00:02:10.560 --> 00:02:14.915 the 10K resistor slows down the discharge and makes it easy. 00:02:14.915 --> 00:02:16.895 Now, let's do the same thing again, 00:02:16.895 --> 00:02:20.800 we'll bring the amp up to full operating voltage, 00:02:20.800 --> 00:02:22.995 which is in this case, 00:02:22.995 --> 00:02:27.400 we see 347 volts, 348, 00:02:27.560 --> 00:02:31.720 and as the two tubes warm up, 00:02:32.450 --> 00:02:35.840 you'll see that the amp will actually drop in 00:02:35.840 --> 00:02:39.480 voltage because the tubes will start conducting. 00:02:39.550 --> 00:02:46.220 Now it's down to 333, 334, 330. 00:02:46.220 --> 00:02:49.700 So this is a normal voltage that you would see in a blues 00:02:49.700 --> 00:02:53.975 junior with normal operating conditions. 00:02:53.975 --> 00:02:58.620 Now, you can play through the amp, it's live. 00:03:00.080 --> 00:03:02.685 Now, if we just turn it off, 00:03:02.685 --> 00:03:06.950 remember we turned it off before when the amp was cold and nothing happened. 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, 00:03:12.590 --> 00:03:16.875 26, 16, faster than it did through the 10K resistor, 00:03:16.875 --> 00:03:19.335 three volts, two volts. 00:03:19.335 --> 00:03:24.530 Why? Because it's conducting through the ELAD force primarily and the other tubes, 00:03:24.530 --> 00:03:29.345 but these guys are always using a lot of current all the time. 00:03:29.345 --> 00:03:35.635 So, simply turning off a warm amplifier is all you have to do to discharge it. 00:03:35.635 --> 00:03:38.010 So, now we can strum it, 00:03:38.010 --> 00:03:39.795 nothing is coming through the amp, 00:03:39.795 --> 00:03:41.850 and this is ice cold, 00:03:41.850 --> 00:03:44.005 I can touch it with confidence, 00:03:44.005 --> 00:03:47.875 know that I'm not going to get knocked on my tail or anything like that. 00:03:47.875 --> 00:03:55.775 So, what about the old myth of having to strum the guitar while you're discharging? 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. 00:04:05.450 --> 00:04:09.970 So, we're stable at around 334 volts, 00:04:11.750 --> 00:04:14.115 and we have a normal sound, 00:04:14.115 --> 00:04:17.139 and now we'll strum while we're discharging, 00:04:19.550 --> 00:04:22.870 the powerful E chord there, 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. 00:04:31.395 --> 00:04:34.450 There is no reason to actually strum the guitar, 00:04:34.450 --> 00:04:38.045 that's just one of those internet myths that gets perpetuated. 00:04:38.045 --> 00:04:41.840 The only thing that the strumming does is 00:04:41.840 --> 00:04:46.910 confirm that all of the current is gone from the tubes, 00:04:46.910 --> 00:04:48.005 but it can be deceptive, 00:04:48.005 --> 00:04:53.645 if you had turned the amplifier on and off quickly and these were cold tubes, 00:04:53.645 --> 00:04:58.120 it would hold a charge and it wouldn't play when you strummed it. 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, 00:05:04.025 --> 00:05:07.190 so you can play through it and simply turn it off, 00:05:07.190 --> 00:05:09.635 that will always discharge it all the way down. 00:05:09.635 --> 00:05:10.970 Don't put it in standby, 00:05:10.970 --> 00:05:12.785 don't do anything else with it, 00:05:12.785 --> 00:05:15.274 and you can play if you want to confirm, 00:05:15.274 --> 00:05:16.850 as the sound fades out, 00:05:16.850 --> 00:05:22.050 you know that it's being discharged and that's all there is to it.