Tube Gear Troubleshooting - Powering Up Using a Variac - Part 2
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- Опубліковано 10 гру 2024
- BG246 - Learning how to use a variac to bring up a piece of vintage tube gear in a controlled fashion. Also, a little on isolation transformers, dim bulb setup, and killawatt units.
Really nice of you to do this. Fascinating. It's great to have the things that you think you know confirmed and to learn a few things along the way. Looking forward to the next one. Thanks.
Mark - now that you're back, I hope you continue with the Tube Gear Troubleshooting series. I find it really useful.
Glad to see you up and at'em again!
Another idea that goes along with powering up with a variac is to pull the rectifier. This way you have isolated the power transformer, suicide cap, and whatever else is nearest the wall outlet from the rest of the power supply and all of the electronics except the tube filaments. Having voltage and current meters on the variac, like you do, is a great help as is the dim bulb limiter. I like your idea of having a dedicated troubleshooting series. Looking forward to all of it.
Loving the new series! Nice to be able to binge Blueglow!! Three videos in an afternoon. I have used a Kill-a-Watt ever since I started this journey, works great, but I like the idea of the multiple display model. Thanks Mark.
Great series!! Please don't forget the Zeus SRPP Tube Preamp project. I built the KT88 Amp, and it's super. Really need a Preamp to match it!
I am looking forward to the next video in the series. Thank you.
Thank you - so very helpful! Looking forward to the next installment.
I know it's kind of randomly asking but does anybody know of a good place to watch newly released tv shows online?
@Jackson Khalil I watch on FlixZone. Just search on google for it =)
@Harlem Julian Yup, have been watching on flixzone for since march myself :)
@Harlem Julian Thank you, I signed up and it seems to work :D Appreciate it!!
@Jackson Khalil You are welcome :D
Before I would even dream of plugging in a set under test, even with a variac and/or current-limiting device, I would make two continuity tests with my VOM/VTVM/DMM across the power plug 🔌 one with the power switch off, and one with it on.
With the switch off, you’d better see infinite resistance (“0L” - overload on a DMM), or STOP -something is wrong!! Either the power switch is damaged, or you have a leaky across-the-mains (“death”) cap, or someone was in the unit before and futzed something up.
With the switch on, you should see about 10-20 ohms (or more). For a set with a “hot” chassis (such as an AA5 tube radio), this is the series resistance of the filaments, plus - usually - a dropping resistor. For sets such as the one in this video that have a power transformer, you’re seeing the (DC) resistance of the primary winding. If you see less than 10 ohms or so, STOP! Again, something is wrong! Obviously, if you get infinite resistance, then either the power switch is bad (or dirty contacts), the fuse/circuit-breaker has tripped, the primary winding is open, there’s a leaky “death” cap, or - again - someone may have been in the set and mis-wired it when they put it back together.
Only after this (and fixing any blatant problems), should you plug an any “unknown” device into mains power! The life (and test equipment) you save may be your own! 😁 HTH!
I'm looking forward to part 3. Great stuff so far.
Thanks Mark this is great. You may be already planning this, but as part of the series, any chance you could do a video on what test gear to have (e.g. dummy load, signal generator, oscilloscope, etc.) and how to operate them?
Thanks! I like this series. :)
Great seeing this series you are starting Mark. Looking forward to the future parts of this. Been doing a lot of solid state lately and itching to get back to the tubes. Can't wait for some new builds from you!
Looking forward to the next video . I am at the same stage here with my own amp. A pioneer sm-83. I hope you can show how to test for problems with the output transformers...
Hi Mark, I would change the electrolytic filter caps and those wax/paper coupling caps. All will be leaking DC current by now, messing up the bias and putting massive amounts of ripple on the B+. Possibly going short and burning up the power transformer, caps are much cheaper than rewinding transformers.
Based on where the fuse "blew", did you consider a mechanical break in the fuse? It could be that old fuse didn't like the handling in transport.
The same crossed my mind as well
I connect my variac up to a flux capacitor, through a Jig-A-Watt meter !
great info and demo! I still opt to have a load connected to the output (speaker) terminal.
Me too. I do it for strictly practical reasons, I am afraid that I will forget to load the outputs once I get started troubleshooting. Gotta know your limitations!
I can't seem to find the specific video I watched of yours so am going to ask here. When using a current limiter (with a light bulb) do you plug the current limiter into the kilowat meter, or should you put the kilowat meter between the amp and the current limiter?
Hello, thank you for this video. Quick question if I may. I have a variac at my disposal. I will be installing two new 400v 3300uf can capacitors in my tube amplifier. After the install I believe it would be wise to slowly bring the voltages up on these new capacitors. The amplifier is not tube rectified. Would you agree?
A permanent soft start circuit might be helpful using that much capacitance, especially if high voltage across cap.I like to slowly apply high voltage to electrolytic cap. With 10k to100k resistor in series and then slowly discharge it before installing the new cap.measure voltage across the resistor with voltage applied to cap.a good formed cap will show very little voltage across the series resistor.(low leakage).
Hello, Mark, where may I purchase a pre-made dim bulb tester?
Thank you
ordering a Kill A Watt right now!
When using all three devices; the Variac, the isolation transformer, and the dim bulb tester, IN WHAT ORDER should they be chained together?
It really does not matter. My setup first goes through the isolation transformer then into the Variac and from there into the dim bulb setup. You do want to be able to watch your dim bulb while bringing up the power so it should go after the Variac but you could put the isolation transformer either between the Variac and dim blub or before everything like my setup is. Good question :D
Thank you Teacher
Could someone please explain how the amp was brought up without any load? I'm not too bright but I thought this meant disaster for the transformer? I'm going to bring my amp up on variac, but it has a center channel, I'm not sure if this needs to be loaded or bridged or left naked?
It's OK to power up a tube amp with no load with no input signal. The damage occurs if the amp attempts to amplify a signal.
I have a fundamental misunderstanding of the dim bulb current limiter.
The incandescent bulb is in series with the test device, right?
So 100% of the current flowing through the bulb is also flowing through the test device, right?
So how does that protect the test device from excessive current?
One property of an incandescent bulb is that the hotter it gets, the more resistance it produces so with a low current draw, the bulbs stay dim and do little to obstruct the flow of current. As the current draw becomes larger then the bulbs get brighter and as part of getting brighter they get hotter and present a larger resistance to the flow of current while at the same time giving a visable warning of the current flow.
Hey, that's very helpful. Thank you.
I've been trying to figure out how to make the tester even more effective by using two bulbs. So the obvious question is, series or parallel.
I suppose two bulbs in series would be best. Then their hot state resistances would add together and limit more current. In parallel I think they would draw more current and send that on to the test device.
Does that sound about right?
Question: So theoretically, if I had all this equipment, I would want to run from the wall into the isolation transformer, then the variac, then the dim bulb testor into the usage monitor. I would then plug any equipment I was working on into the usage monitor. Do I have this in the right order? A UA-cam guy, that has a name that starts with Mr. and has a lab, stresses the isolation transformer over everything else. Another, that has some seriously good guitar playing cats, seems to favor the dim buld testor over everything for working on guitar amps. You seem the feel the variac is the most important. Is it silly or redundant to run with all three?
I’d suggest that Mr Carlson’s emphasis of the isolation transformer is 100% pure gold advice. I would recommend that the isolation transformer be the last device in the chain since some variac / auto transformers could very well internally reference their output circuits to earth thus negating the earlier isolation provided if you placed the isolating transformer at the start of the chain. If you are absolutely certain that all subsequent devices downstream of the isolation transformer do not connect / reference any parts of the circuit to earth / ground then it’s fine to place them after it. The safest belt & braces approach is just to place the isolation transformer last and plug your equipment under test direct into it. Hope that helps.
Tenspeed TheBikeHanger Just to add that each of the three devices is serving a different function:
1) Safety isolation ( protecting the human )
2) Current limitation ( mainly protecting the equipment but human benefits too )
3) Voltage / current / power monitoring ( information)
So each has its distinct value and use.
@@brencostigan Thanks!
Mr. Carlson actually uses all three all the time. I like this idea. His power for the Device Under Test is an all in one unit. As mentioned, the components all used together provides three modes of protection, to you, to test gear, and to the DUT. Some of the other You Tube electronics repair guys have bypass switches or have their trio of AC power up gadgets so that they can plug or unplug them into different orders.
I would tend to start from the wall outlet to first go to the variac, then the isolation transformer, then to the dim bulb limiter, or else copy Mr. Carlson's setup.
@@brencostigan Well, to my understanding yes and no. If you place the isolation transformer first and its output is truly isolated from earth and nutral as the output should be, then there is no way for anything down stream to reach earth regardless of how they are wired internally because the power circuit they are wired to after the transformer has no connection or reference to nuteral or earth. It will NOT HURT to put it last though, not at all however if it is a real isolation transformer then there is no difference. YMMV! ===|} {|=== No physical connection to the power source at the wall.
Where there's smoke, there's fire. Always a bad sign!
Mark, you okay Boss? Buddy check....
1. Check and see what blew the fuse. (continuity check). 2. DON'T power it up until *ALL* caps. have been changed! Caps. are cheap!
I've never seen a very act like the one on your bench where do you find things like that
variac I have never seen one like that
Greetings:
You fail to mention whether there is a power switch or gain control. An ohmmeter test between Line and Neutral power switch ON, will show any obvious reason for the blown fuse.
You do not address connections to the input and output connections. Nor do you check for output (speaker) impedance. I would start with the input shorted and some nominal resistance (typically 8 ohms) on tthe outputs.
The first and most vital piece of equipment for work bench is a 'safety switch' a.k.a. GFCI, RCCB, ELCB. These devices monitor the current flowing in the live and neutral lines of the mains supply. If these differ, current is going somewhere it shouldn't, and the switch kills the current immediately. If that 'somewhere' was through your body you could die without the safety switch. As for isolation transformers, they can introduce more hazards than they prevent, particularly if you use an oscilloscope. Unless you are working on a hot chassis or a switched mode power supply, you are safer without an isolation transformer. I'm an amateur tube jockey, so why should you believe me? Read the article written by a man who has been designing, building and repairing electronic equipment for over 40 years at: sound-au.com/articles/iso-xfmr.htm
Nice!! Fun!!
Way late to the game here, but I think your comments about the dim bulb tester are dangerously misleading.
The dim bulb tester will do nothing to protect _you_. If the bulb lights up at 0.5 amps and you yourself are the short, you're already dead. It takes maybe 100 mA to kill you.
The dim bulb tester is really only to enable you to see if there's a fault in the equipment. If you have, say, a short in the device, it will pull enough current to light the bulb and you can flip it off before you actually burn something out.
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