Capacitor Leakage Tester built from a Popular Electronics article with modifications. Originally intended for testing capacitors in TV sets of the 1950's and 60's.
Just subbd Tom, awesome series for the classic frugal radio stuff! I am an older electronics guy myself with a background in electronics but not to much with classic radio repair until now in my retirement. So enjoying your series and thank you so much for sharing such cool knowledge. (-Tony)
fantastic vid very useful device and well presented thank you (subscribed) one small point you said ''variable isolation transformer most people call variacs'' most variacs are not isolated they are auto transformers as you rightly said in the vid i know you know this just didn't want anyone to misunderstand.
one quick warning. If you need isolation, despite what you said..a Variac does NOT provide isolation..it is an autoformer...and since there is only one winding, there is no way to have an isolated output. there are units that combine a isolation transformer with a Variac. those units DO provide isolation.
You are correct and you can't remind people enough about this. I use a Sencore PR57 as you see in my videos which provides BOTH isolation and variable voltage. But it can't hurt to say it again and again since I think some people don't actually pay attention to the videos and might think that any variable transformer provides isolation which is not necessarily true. Also, we shouldn't really be calling it a Variac since that is a trade name registered with the US Trademark Office. We really should say Sencore PR57 or use the generic term," Variable Isolation Transformer." Thank you for reminding everyone.
Thank you for providing this video...you do such a great job presenting/explaining things!! And I love that you stress so often and emphatically the need to be careful with such electronics. Far to often, I find that other channels are too flippant about safety...perhaps because they get tired of mentioning it, or don't want to get the negative criticism in the comments. Is there any reason you would not have used a three-prong wire and grounded the chassis of your box?
Mr. Tom appreciate your articulate, enjoyable videos. Would you please suggest what wattage resistors in this project should be? Even the '59 article doesn't say. I want to assume-considering current draw-that even 1/2 watt might be ok. The 3.3k though, has me stumped. God bless...
Great video can I ask a question. I am in the UK could you recommend an alternative to NE2 or NE51 as they don’t seem to be available here. I would like to build both of your cap testers, many thanks for the videos and presentations. Go safe.
I built one following your schematic exactly. It did not work as I got a small reading of volts & minivolts. I changed the direction of the diodes, thinking that would solve it, but to no avail. It's a letdown as I really wanted to have one handy.
Our line voltage down here is already 220volts. An isolation trans 220-220 would be nice but is not ordinarily available. So maybe a 25 watt bulb in series with the line would suffice. Am i right?
Tom! On “your” schematic, you say that when the switch is switched of, that it discharges the capacitor.On the original schematic, I can see that the push SW does discharge the cap.But on your version where does it discharge to.Or am I completely missing something? I would like to build your version. So perhaps you could let me know how it discharges on your version. Thanks for all your vids.Boy am I learning about electronics! Wish I was 24 instead of 74! 👍
In the final version I used a DPDT switch that shorted the test leads when in the non-test position. I don't have time now to check but I thought I said that at some point in the video. But if I didn't, I should have. Thanks for pointing it out.
I will try to answer both your questions here. Putting a lamp in series with the line helps protect the circuit from over-current in case of a fault but really does not replace the safety of an isolation transformer. Please take a look at my video "The Death Difference" for more. A lamp in series will reduce the output voltage of the tester so you can test units with lower voltage ratings. You should check the actual voltage of your tester with the lamp in series to see what it is since testing at too high a voltage can ruin a good capacitor. For example, the DIY Tester should not be used on low voltage capacitors (less than about 150 volt rating). As to replacing the neon bulb, the neon bulb has the advantage, not only of lower cost, but also faster response. Smaller capacitors will charge quickly, so a meter is a little slow. For example, if a small capacitor has a little leakage, the neon bulb will blink every so often, but a meter would probably not budge. An ammeter will show steady leakage or a short, however. A voltmeter will not work too well since you are trying to test for leakage current. Hope this helps.
Thanks for the reply. I will always keep those facts in mind. I am in the process of restoring a Pioneer SM Q300B bought in the early 60's. My sister's family stowed it away in a rat infested house. No choice but to completely disassemble and repaint the chassis. Not too keen on restoring the dual am,fm and sw receivers at the moment. But the amp sounded great at the time. I actually cloned it in high school but the factory matched components and output transformers made the difference. I had to wind my own power transformer since it was not available commercially. This capacitor tester would be used to test and reform salvaged power capacitors for future use.
I like to see this vintage equipment restored to its former glory and I wish you well with this one. I am glad the tester will have a place in the restoration. I assume you know the importance of care in cleaning equipment that has been exposed to animals - respirator when scrubbing, gloves and disinfectant until no traces of the animal leavings remain. Let me know how it goes.
This tester was originally designed to test high voltage >250 volt coupling capacitors used in TV sets. It also works well for high voltage bypass capacitors. It was never intended to check electrolytic capacitors although it can be used by a skilled person for electrolytic capacitors as long as that person understands the difference between film capacitors and electyrolytic capacitors both in terms of their leakage and charge characteristics.
also finds leaky if transformers with silver migration desease, hook up one lead to primary and one to secondary with transformer out of circuit,light will come on or flash if transformer is bad, I made one like the orig.design years ago,its really a q&d tester for finding lots of problems.
Thanks for the comment. I agree. The same tester will also reveal primary to secondary leakage which will upset the bias in an old TV so badly the sync pulse will be compressed due to overloading. Strange to find what looked like a problem in the sync circuits was often really an if transformer leakage problem allowing B+ from the primary to leak onto the secondary..
I would use the Sencore LC102 which can put up to 999V on the capacitor for leakage. Sencore also made an LC103 that would work but I do not have one, so I would use the 102 set to 999V.
Good question and the answer is no, because the tester uses full AC line voltage, it will only work on capacitors of approximately 200 volt or higher ratings. The tester was originally intended to test capacitors used in TV and radio sets made in the 1950-1960 era, which usually had paper caps rated at 250 volts or more. It is definitely not appropriate for transistor or other low voltage capacitors. There is a danger that it could actually make a good low voltage capacitor bad by over stressing it. I would not use it on any capacitor rated at less than 200 volts, which is the approximate open circuit voltage at the test leads when the test button is pushed. This assumes that the tester is built for and used on a 120 volt AC input line.
Excuse my late question: with a variable transformer (plus isolation, of course) you mentioned in the video much lower voltages could be applied to the cap, eg 50. Is 10v off the “Variac” any different?
You are using high voltage on the testleads, with a metal housing, and with the positive lead almost touching the metal housing while you are handling the tester. Seems very safe working........NOT
Thank you for your comment. I am glad to see that you understand the lack of safety in these vintage designs. Even if you use an isolation transformer as I suggest, there is still a need for inexperienced people to avoid projects like this old one and buy modern, safer equipment.
15:40 "as good as hobbyist can afford" that's the same stuff even highest quality electronics producers can do, offcourse these days it's mostly cheapest lytics in cheapest devices... ie there are no better quality lytics than japanese
