How to safely power up an ancient lab power supply? - Page 1
Forum section: electronics / general

author: jippie
author_rank: Unknown
timestamp: December 25, 2013, 10:17:55 pm
content: With ancient lab power supply I mean one from the tube era that hasn't got a single semiconductor in it. I found it in my parent's attic and I want to turn it on to check if it still works. Now I understood that you have to be careful powering up such old equipment after it has been turned off for tens of years. At least I am aware that the capacitors need to (don't know the proper English word) revitalize slowly. But how can I do that without taking the device apart?Is there a general good procedure to follow to power up very old equipment? Anything to watch out for? I don't have any manuals or diagrams, so I really don't want to break it. What is the best way to clean its in- and externals? For what it is worth, I know 100% sure that the power supply was in fully working order the last time it was switched off.Pictures are inthis message.

author: houdini
author_rank: Regular Contributor
timestamp: December 25, 2013, 10:29:51 pm
content: Use a variac and bring it up slowly.

author: jippie
author_rank: Unknown
timestamp: December 25, 2013, 10:38:53 pm
content: Quote from: houdini on December 25, 2013, 10:29:51 pmI have to find a variac, unfortunately I don't know anyone owning one. Define slowly, is that 0-230V in a few seconds, minutes, hours, days ...?

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: December 26, 2013, 12:54:04 am
content: Use a lamp-limiter - simply a mains light bulb in series with the load. You need an incandescent light bulb, of course, not a modern energy-saving type. Do a search - there are plenty of vintage websites out there that explain this...Mark

author: don.r
author_rank: Frequent Contributor
timestamp: December 26, 2013, 01:00:42 am
content: also called a dim bulb tester...http://antiqueradio.org/dimbulb.htm

author: TheBay
author_rank: Unknown
timestamp: December 26, 2013, 01:19:01 am
content: +1 For variac. Not often mentioned much these days, but every bench should have one.

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 26, 2013, 07:29:47 am
content: Quote from: jippie on December 25, 2013, 10:17:55 pmJust open it up and give it the quick once over, check the tubes to see if they still have the metallic deposits at the top to make sure they havent leaked, if its built on a board, check for bad joints, if it has electrolytics, just check them, with a continuity meter to make sure they haven't gone short.Then bring it up slowly on a variac.

author: Psi
author_rank: Super Contributor
timestamp: December 26, 2013, 09:15:43 am
content: There's a pretty good chance a cap will blow after a few seconds/minutes.I would turn it on after a quick look inside, but only for long enough to confirm it is in working condition. Then i'd take it apart and replace all electrolytic caps along with any other parts that look a bit suspect.It would be a good time to check and fix any safety issues you see, things of that age were usually designed without any concept of electrical safety

author: jippie
author_rank: Unknown
timestamp: December 26, 2013, 09:24:04 am
content: Quote from: Psi on December 26, 2013, 09:15:43 amI want to try keep it in its original state as much as possible. It isn't very useful for a bench power supply anyway with its longgg start up time and poor efficiency. But it would definitely be nice if I can show it is working.

author: Psi
author_rank: Super Contributor
timestamp: December 26, 2013, 10:02:04 am
content: I wasn't meaning lots of mods like adding MOVs/polyfuses etc..Just checking over the mains wiring and perhaps adding some insulation around anything that may easily short to the case.Also checking the earth connection is done properly with restraining clip so it cant pull out.That sort of thing.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: December 26, 2013, 10:42:16 am
content: The trouble with using just a variac is that it doesn't limit the current that flows, and there are any number of components that could be damaged before you realise that something is wrong. Heavily leaking smoothing capacitors can damage rectifiers and ultimately explode!I definitely agree that variacs should be more commonplace in our workshops - I have one - but for old gear, the simplicity of the lamp limiter/dim bulb tester (hadn't heard that term before - thanks) can't be beat. I use my variac in conjunction with a lamp for old gear - eventually I plan to mount them both in one case, along with some metering, as a combined AC voltage source suitable for safely powering up all sorts of gear.Another good reference:http://www.vintage-radio.com/projects/lamp-limiter.html

author: Kevin.D
author_rank: Frequent Contributor
timestamp: December 26, 2013, 10:52:36 am
content: If there's large electrolytic caps the insulation between electrodes can degrade when standing uncharged for long periods so when you turn on first time these caps can draw very large leakage current or be almost short ,the insulating oxide coating can be reformed if you put a smaller voltage on them and allow to stand for a period before your first full turn on .Just google "capacitor reforming".