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PostPosted: 12 Dec 2013, 07:58 
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I like to use the meter probes that are long and skinny with insulation covering all but the last 1/8 inch of the probe...good for reaching into P2P amps.

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PostPosted: 02 Feb 2015, 19:27 
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Basically, test, test, test, and test some more. I do self designed builds. The A Number One thing not to do is slap it together, hit the power switch while praying. Bad idea, and I knew someone once who tried constructing a colour TV kit in just that manner, and he could have bought several with all the money he spent trouble shooting that thing, and it never worked.

Here's how I do my projects:

1) After mounting the hardware, I first wire up the heaters. Check and check again to make sure the right pins are connected. If there are other secondaries, tape these off and get them out of the way. Plug in the tubes, and power up. Make certain all cathodes are glowing.

2) Next, complete the power supply. Again, make certain everything's connected correctly, and pay special attention to the polarities of all electrolytics. So far, I haven't lot a one, but found several with reversed polarities occasionally. If using solid state, also make certain the diodes are connected for the correct polarity. If this is a solid state supply, then a 100W light bulb in series with the PTX primary is a really good idea. It should light up brightly for a second or so as the filter capacitors charge up, then settle to a dim glow. At that time, measure the DC voltage(s). They'll be low, but should be there in proportion to the actual primary voltage. If that looks good, try it at full power. Hollow state PSs with integral diode heater secondaries can't be tested this way, since that'll make the heater voltage too low, and cold cathodes compromise both PRV and Isurge ratings. You could get a nasty flash-over with an abnormally cool cathode. In that case, a clip on AC ammeter is advisable to make sure the primary current is in line with the expected value. If it's excessive, then something isn't right, and you need to find out what that is before powering up.

3) Begin wiring the circuit itself. If using any solid state CCS's as active loads, it's best to complete these first and test to make sure they're working as expected. I use 9V batteries connected in series for this, and variable resistors to make sure the current really is constant, and within design nominal values. I've found this is especially important when using those multipacks of diodes from Rat Shack, as I've seen bad ones in there. Same goes for those "transistors anonymous" packs they sell.

Complete the first pre, always checking the wiring for correctness, and power it up. O'scope to check for undistorted output, voltage gain, and check for parasitics. Make sure its right before proceeding. Test every stage as it's completed to the finals.

4) If it's a design that includes feedback loops, be certain to connect a large load resistor to the output because Mr. Murphy is certain to have connected it for positive feedback more often than not, and you don't want to pump max watts into speeks when it behaves like a 50W Royer oscillator. O'scope and make certain that there are no signals at both the secondary and primary of the OPT that shouldn't be there. Depending on the finals, you sometimes catch snivets at the primary (looks like "bubbles" along a sine wave when testing with a signal generator).

When doing solid state projects, always bring up the voltage with a variac. Transistors just love to oscillate at radio frequencies, and when they do they poof faster than any fuse can blow. You need to catch that before it can build to a level that'll poof the finals.

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PostPosted: 08 Oct 2016, 13:34 
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Joined: 14 Sep 2016, 15:12
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I may have overlooked this advice in the earlier responses but I always use an emergency stop with a (red coloured)mushroom head.
This stop I have mounted on a piece of wood and placed it under my lab table as near as possible to my feet.
This switch interrupts the mains voltage to my test chassis. And in case of disaster, I only have to push the mushroom head with one
foot to switch off the mains voltage.
It is really a life saving set up!


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PostPosted: 10 Oct 2016, 13:31 
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Mpfffff..... Lots-O-Good stuff here. But, not (in my opinion) distilled into a single process. I will *try* to do so, and I also invite any-and-all suggestions or improvements.

First, I will describe my set-up for first test - together with a little background:

I came into the audio hobby by way of vintage radios. I always enjoyed audio, but as a purchaser-of-stuff vs. a builder-repairer-of-stuff. That came as a natural outgrowth of the vintage radio hobby. Most vintage radios in my collection are tube-based, some go back as early as 1919, but as to mains-powered radios, to 1928. Filter caps of that vintage, electrolytic caps of any vintage other than yesterday, and such are always questionable, and often shorted. "Just Plug It In" lets out the magic smoke in short order.

From the wall, I have a 1900 box that includes a regular duplex receptacle and a 15A GFIC device. This provides ground-fault protection if necessary. That, in turn, feeds a Heathkit IP5220 metered ISO(!!)-variac with two ranges 0-1A and 0-3A. For the record, I have only one audio device that exceeds 3A in regular operation - that would be my Citation 16 amp.

So, when a new-to-me device comes to the bench, I will plug it into the Heath and start at 0-volts. As I bring it up, I keep an eagle-eye on the ammeter, if it starts to spike, I can turn everything off well before any damage is done, or any smoke escapes. Further to that, each range is separately fused, adding a small additional level of protection. After a number of years using this device and observing the behavior of various components on power-up, the process becomes predicable such that when it deviates from the proper path, it becomes obvious.

Example: Most well-behaved items with tube rectifiers will show a small current draw increasing in a linear fashion to the voltage *until* the rectifier starts to pass DC. Then, there will be a fast, but orderly ramp-up until full operating voltage is reached and the filter caps are charged. This IS predictable with a narrow range based on the type of device, number of tubes, type of tubes and some other basics. If the current passes that predictable range, or "hunts" - there is trouble. And with SS rectifiers, with each voltage rise, the current draw will jump, then fall back, jump, then fall back to the proper range, all things being good.

So, at the very least, this will allow any new device to be tested at a very low risk, and even save fuses as the device should never reach the point where a fuse will be blown. I cannot imagine doing it any other way with any degree of safety. I cannot imagine testing anything without the ability to measure current within a very few watts. And, for the record, a 1936 6-tube Zenith radio that crossed my bench a few weeks ago came up on the Heath drawing 160 watts at 105V, and actually played with only a little bit of hum.... and within 30 seconds of noise, that needle started to creep up yet more (all predictable after 30 years in the hobby - so going to 105V was only to find that 'creep' point). After recapping, cleaning and some other minor repairs, it pulls about 35 watts quiescent. I wonder where that extra 125 watts was going (not really)?? Point being that the moment a 6-tuber exceeded 50 watts, I knew I had a problem.

Cutting to the chase: Critical to initial power-up, one needs:

a) A means to protect the user against ground faults - GFIC, at least.
b) A means to isolate the user from Line-Hot or Line-Neutral - Isolation transformer.
c) A means to control voltage accurately.
d) A means to measure current accurately and in tiny increments.

However one does it, these are the basic means that MUST BE included for both basic safety and then protection of the test piece. Anything less puts one or both at risk. There are any number of ways to get there, but get there one must if one chooses to indulge in this hobby.


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PostPosted: 13 Feb 2017, 06:20 
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I haven't read the proceeding posts but here is my method for turning on tube amps for the first time; Absolute number one, check and re-check your wiring and compare it against the schematic, use at least two meters - an analogue for the HT and digital for the filament voltage. AND clip lead to the test points, no fingers in the machinery.

When the power comes up and be ready to pull the plug if voltages etc. are not within expected range. Also look away on power up. If a cap goes off you could lose an eye.

But careful wiring and double checking that against schematic can go a long way to a safe maiden voyage.

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PostPosted: 22 Oct 2017, 23:54 
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Joined: 23 Feb 2017, 02:02
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No one had recomended this, but I recomend wearing plastic gloves whenver the amp is turned on.
Some sort of thinn latex glove are good, dosen't stop you from manurvability but gives you protection from high volts.


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PostPosted: 15 Sep 2018, 23:15 
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Joined: 13 Jan 2018, 21:33
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Location: australia
I have practically reached the end of assembling my cheap 5u4g/6sn7/300b pcb amp mentioned on this site , well not so cheap when transformers and 300b tubes are factored in. I've never really wired up anything before involving mains power so I played it safe and handed over to a guitar amp builder to check if I done anything wrong that would make it unsafe to use or bad to listen to. It feels a bit unsatisfying that I'm not completing all of the stages myself but I don't have the equipment mentioned in this thread that would make this possible and once copped 240v from a toaster when young though I careless at the time. I will try and educate myself more for the next build but i reckon some practical hands on experience with someone who knows what they are doing safely would help a lot . I am not aware of any ways to go about this but there must be I guess. Are there any alternative ideas or ways to go about this available for the newbie DIYer?

Regards

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PostPosted: 30 Sep 2018, 10:46 
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Joined: 13 Sep 2018, 17:11
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gofar99 wrote:
Hi, If you are looking at this forum then you are likely to be both using tubes in projects and doing some diy builds.The subject of how to do a first power up (or power on if you rather) comes up from time to time. There are many ways this can be done. I will tell about how I do it as I have numerous occasions during the developmental process for the projects I post. My way is not the only way, but it works quite well for me. This method was developed over several years to do two things. First to make sure that safety is paramount. Getting fried by a project is not a good thing. :blush: Second to minimize false indications that a project has problems on start up when it really doesn't. A typical thought process is to test each portion of a project separately. Fine, but tests of power supplies in tube gear can damage some components if there is no load and at the minimum give false readings. As a third, but not primary focus, the procedure has so far prevented any serious damage to the projects. For sure I have cooked a few small resistors, but major and / or costly components never.

1. First, most importantly check the wiring. Verify that the correct parts and wires go to the right tube pins. Check the drawing or schematic against the build.

2. Turn the thing upside down and shake it to remove any loose wires, parts or solder.

3. If it uses tubes, put them in place. This is not intuitive and seems like the wrong thing to do. The reason for doing this is that some voltages, particularly the B+ ones on the various tubes will not be correct if there is no load. Worse, you may exceed the ratings on the filter caps if there is no load as they will charge up to the peak voltage (and not the normal operating voltage). If you think about this a bit.... tubes are quite rugged and usually can handle severe operating conditions for a while. They are not usually in danger from faults during an initial start up and voltage check.

4. Attach at least one meter and really as many as you can to key points in the circuit. I use the B+ going to the first filter and the B+ to the last filter as a minimum.

5. Be sure to fuse the equipment. I use slow blow fuses in the AC mains side of the transformer. Usually 3-4 times the expected current level. I use 4-5 amp ones in the KT88 mono blocks (they draw just over 1 amp in operation). This is because there is a very large initial surge on power on. The filters in the B+ chain are a virtual short circuit when you use solid state rectifiers, plus the cold heaters have a far lower resistance than when they are fully warmed up. I find this size fuse to be about right. If you have a serious short or failure it will blow in fairly short time. Remember tubes are really rugged. Too small or the wrong type of fuse will lead you to believe there is a fault when there is none.

6. Now this is important. Do not plug in the project. First turn on the power switch if it has one. Then if you use IEC power cords like I do (those are the ones that you see on desk top PCs). Attach the end that is going to the chassis first. Now, do not touch any part of the project (in case there is a serious fault and the chassis gets energized). Now plug the other end of the power cord into the AC mains. The reason for this procedure is to insure that you do not become part of a potentially energized circuit with potentially serious consequences. Some folks will use a Variac to power up the first time, I do not (even though I have one) as it really didn't protect the project all that much (still had to see if the fuse blows....) and didn't add to the personal safety issue.

7. If the fuse blows, you have a fault and need to find it. Do not touch the chassis, pull the power cord out at the mains end. If the fuse does not blow proceed to the next step.

8. Check the meter readings. If OK proceed. If not shut down by pulling the plug - still not touching the chassis.

9. At this point I like to get a meter and check for AC voltage between the chassis and a known AC ground. Just in case. :)

10. Now you can start to verify other circuit values, like heater voltages and such. If something is way off, shut down and hunt for the problem.

11. The next step is to make any adjustments that are required like setting voltage regulators for the exact values wanted. Virtually any circuit - even those with large power tubes will not be harmed during the short interval needed to do the previous checks.

12. Now you can hook up inputs and outputs to see if the project works.

13. Something not usually critical, but that can be important if the project is a power amplifier is to put a load on the output connections. A fixed resistor is fine. I use 40 watt 8 ohm ones for this. The reason is that some amplifiers will be unstable and oscillate without a load. Not generally harmful, but it can throw off the voltage readings. (BTW, Oddwatts are stable with out loads). Another similar hint that sometimes matters is to short the inputs to an amplifier so it will not see any input signal (noise or hum) on start up and cause the voltage readings to be off.

I hope this procedure will be of some value to you. If someone has others let's hear about them. Like I said at the start, there are several methods to do this.

Good listening
Bruce


Howdy, A great tip on the exchanged outlets. I do have devoted exchanged outlets, yet figured the average diyer would not. I likewise utilize an APC H10 AC mains control conditioner before the switches


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