Post by RdM on Mar 31, 2020 21:58:35 GMT 12
I wanted to make an electrolytic capacitor reformer so I went looking... first one was
(I used a print edit extension to clip everything except the article itself, used large images, and made a pdf.) drive.google.com/open?id=1FRoIoKc0Vgh3TvFZZafSBDOgvU8EZ9p7I was going to build this, bought some 18K resistors (10K & 8.2k) and had a 9 position switch - thought I could skip the 600V step and make the discharge switch separate, and happened to have a 110V transformer and diodes, but metalwork for the chassis was taking a bit long, so I put that on hold and ended up making a combination of these two: www.electrojumble.org/reforming.htmwww.vintage-radio.com/projects/capacitor-reformer.htmlI used an HT transformer with a CT secondary, full wave rectification giving about 400VDC. That feeding a string of 5 75V zener diodes and 2x 12V (or was it 15V & 12V?) which were the only things I needed to buy. Everything else from my "junk" box - chassis (an old valve amp PSU, stripped, that had had an upright HT, & 6.3V heater transformer, a 12 Henry choke, tag strips, and two old electrolytic caps, the holes for which I cut out to put the drop-through transformer in) - and all the rest, switches, knobs, big old resistors, &etc. to hand, I made a switched current limiting resistor setup to select 50-40-30k but have only used it on the 50k setting so far. I was in a hurry so have just penciled in the function labels. It works very well. I start with 150V (450V cap) and monitor leakage current, then when it's slowed right down (to a figure less than the 'modern' table on the electrojumble page, even the NOS Elna 3 section silver can cap in one of the pics) and then ramp up the voltage and monitor again. Top voltage about 400V, but I'm comfortable that enough reformation has taken place that at any higher voltage in use it can finish off in place. (I reformed each section separately.) I built it to aid in the restoration of a Model 543 amplifier from a Wurlitzer 2600 jukebox, perhaps a separate post in itself, that I'd already installed one of the NOS Elna caps in, and had second thoughts about applying full HT to after several decades unused. So after testing, reforming a duplicate one as seen, I then undid my work to reform each section of the installed one (front right). The other ancient ones (100uF) have been removed and will be replaced by a pair of 270uF 450V modern ones, one getting reformed in another pic. It's a voltage doubler arrangement. Those cans also had a 25uF 50V section for (shared) cathode bypass, one per channel. I'll install separate ones right up by the output valves. I ran into a catch-22 situation initially with the reformer. I wanted to use an old 100uF cap as filter/reservoir, but not without reforming it itself!
So I used a 4.5uF 450V polypropylene cap I had to hand first, then added the reformed 100uF. I'm very pleased with it.
I feel a lot more comfortable using old NOS or even modern caps that have been sitting around a few years now, especially seeing how the leakage current starts out and rapidly diminishes. I give it a few hours per section, but the transformer barely gets warm, so I can leave it and do other things. I did have one mishap where the installed junkbox neon got hot, melted, shorted, and blew the fuse. Possibly an overheated internal resistor, wrong voltage. I see this initial discolouring in the underneath pic, in retrospect. Yet to replace with an LED running off the 5V tap.
Some pics:
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Post by colinf on Apr 1, 2020 20:21:59 GMT 12
Looks interesting...Lots to read. Will check it out in more detail a little later!
AMR-iFi R&D
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Post by Owen Y on Apr 1, 2020 20:41:11 GMT 12
I started reforming filter caps with my Leak Stereo 20, in-amp using the cct below, checking voltage drop (leakage) over a few hours. I have sometimes used a variac on amps, again with caps in-situ. I still have a Heathkit Capacitor Checker, which can be used to apply a range of voltages to caps - but this old device probably could do with some restoration itself! 
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Post by colinf on Apr 2, 2020 19:48:21 GMT 12
Hi RdM, nice unit. How did you go about cutting the hole in the steel chassis for the Tx? The organ amp looks like an elaborate unit. The tables defining leakage values for typical caps would be good to keep handy. To repair the oxide layer in a cap I usually set the voltage the cap needs with the amp’s own power supply and add a large resistor in series with it, say 100k for a 50uf 400v cap. That serves 2 functions, to limit the current and to provide power limiting within the cap. So if the cap is leaky the voltage across it will be low so it avoids self-heating and increasing the leakage current. When the oxide re-forms the voltage across the cap automatically increases while keeping the cap cool. Usually it’s about an hour but some caps take up to a day. If they take over a day it’s time to use a new cap. Otherwise, without a cap restorer box or delving into the innards of the amp with your soldering iron, an old valve amp can be switched on ‘slowly’ with a variac, without the valves in it, valve rectifier replaced with a solid state plug-in one, with a resistor in series to monitor current, and checking for excessive current draw. Old transistor amps that haven’t been switched on in a long time really should have the caps done with a cap reformer box gizmo. Class B and AB transistor amps work with lowest distortion with newer, low impedance caps. Even though the old ones work fine, the ESR increases over time and more class B switching distortion gets onto the power supply rails, which then gets into the input stage, degrading its performance. I’m thinking of changing the caps is the Sansui at some stage.
AMR-iFi R&D
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Post by RdM on Apr 5, 2020 21:25:57 GMT 12
I started reforming filter caps with my Leak Stereo 20, in-amp using the cct below, checking voltage drop (leakage) over a few hours. I have sometimes used a variac on amps, again with caps in-situ. I still have a Heathkit Capacitor Checker, which can be used to apply a range of voltages to caps - but this old device probably could do with some restoration itself!
Hi Owen!
Apologies for the late reply, same to ColinF shortly;-
I have a Heathkit R-C Bridge Model C-3U which has a capacitor leakage test function as well as bridge measurement functions, could this be the same one as yours? Yes mine needs work to function properly too. All those drifted 10% tolerance carbon composite resistors, let alone capacitors! I've found before that the really high R value ones drift upward the most, some around the magic eye tube to look at.
(I also have a Philips GM 4144 but it has no varying voltage leakage test function, just another magic eye R-C bridge, superseded by modern devices, also needs work.)
Well, I was going to ask around, what favourite schematic sketching programs people might use, simple and useful for valves, while I was posting, thinking to draw out the schematic for what I eventually built, I looked through a few available for Linux (MX Linux on this box, Ubuntu Mate 18 on a laptop, Win 7 & XP on other PCs) or Windows, the Linux offerings all seeming hideously complex, I don't really need a whole PCB suite yet, I know there are simpler Windows ones, a friend still uses Win 98 as well as XP, I forget the programs, I'll ask him.
Dear old Patrick Turner who I read for many years in Usenet rec.audio.tubes simply used MS Windows Paint as I recall. (Hmm. Who or whom?)
Perhaps he built up a library of symbols for that, I don't know.
Now having this afternoon discovered the fountain pen thread, and observing your schematic sketches, I may as well just write it out and capture, for immediacy, I think. Well, I would have wanted to sketch it out before entering or transferring into a program anyway. I pretty well built it in my head from absorbing the above links, checking as I went. (I still made a couple of mistakes;- I first connected the zener diode string without a current limiting resistor - that blew most of them, all but two, replaced and OK after that.)
(Second mistake was getting a shock, before I'd remembered to connect a bleeder resistor, just a few hundred volts DC, I've had it before but still a not nice stupid tingle!!)
I wouldn't use a variac on a valve amp without removing all tubes, and then if a valve rectifier substitute SS diodes, because what results with heaters (or filament rectifier) at low voltage? Even then, surely you want to measure each filter section caps leakage separately, so I don't see the point, it seems a bit lazy, to sort of maybe save time, into the unknown, hope still?
That said, a friend has just loaned me the first variac I've ever had my hands on, not used yet...
Well, in this case, I undid my connection work on the replacement 3 section NOS Elna so that I could reform each section separately, and was glad I did.
Took photos, but a little too much effort to upload now, I might later.
Likely a separate thread on the amplifier restoration. I think I still might need advice yet.
Regards and thanks, ~ Ross M
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Post by Owen Y on Apr 5, 2020 21:46:59 GMT 12
Hi Ross RdM - this is my Heathkit Capacitor Checker - Model IT-28... 
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Post by RdM on Apr 5, 2020 21:47:17 GMT 12
Hi RdM, nice unit. How did you go about cutting the hole in the steel chassis for the Tx? The organ amp looks like an elaborate unit. The tables defining leakage values for typical caps would be good to keep handy. To repair the oxide layer in a cap I usually set the voltage the cap needs with the amp’s own power supply and add a large resistor in series with it, say 100k for a 50uf 400v cap. That serves 2 functions, to limit the current and to provide power limiting within the cap. So if the cap is leaky the voltage across it will be low so it avoids self-heating and increasing the leakage current. When the oxide re-forms the voltage across the cap automatically increases while keeping the cap cool. Usually it’s about an hour but some caps take up to a day. If they take over a day it’s time to use a new cap.Otherwise, without a cap restorer box or delving into the innards of the amp with your soldering iron, an old valve amp can be switched on ‘slowly’ with a variac, without the valves in it, valve rectifier replaced with a solid state plug-in one, with a resistor in series to monitor current, and checking for excessive current draw. Old transistor amps that haven’t been switched on in a long time really should have the caps done with a cap reformer box gizmo. Class B and AB transistor amps work with lowest distortion with newer, low impedance caps. Even though the old ones work fine, the ESR increases over time and more class B switching distortion gets onto the power supply rails, which then gets into the input stage, degrading its performance. I’m thinking of changing the caps is the Sansui at some stage.
Hi Colin, thanks for the nice reply.
It was an aluminium chassis, and I just used a nice new metal hacksaw blade in my jigsaw, drilled starting holes in corners first. Can't remember if by hand to a drawn line or with a guide rail, I think the former, filed afterward.
Yes, I've just got 50k max at the moment, and I only built it with valve amps in mind at the time. I think on advice (one of the articles) it useful to ramp up in 3 voltage stages to max, checking each progress in leakage current;- anyway, that's what I did.
Yes my thoughts too on a variac with valve amps (as above;- with all valves out, an SS rectifier substitute), but it's still a punt if there is excessive current:- which capacitor? So I elected to test each section separately.
Good point, reminder, thank you, about lower voltage higher uF caps in transistor amps! I think maybe I have to make a lower voltage (selection) version for those! I've been troubled with fleeting maybe thoughts of perceiving distortion in even my current system(s), dating back to early '90s, so something to look in to.
(For instance, bringing a Sony TA-AV670 bought new in 91 or so out of retirement (for strange intermittent faults) recently after decades as a substitute for a s/h TradeMe Denon AVR-3000G with smashed and repaired but yet still scratchy volume control, yet with more inputs, temporarily. Apart from intermittent oddities, I wonder if slight distortion... )
(And yet again, my Sony plain TA-F540E stereo amp, perhaps Sony's 100W answer to the Pioneer A400, has been collecting dust and possibly atmospheric kitchen grime for years, goes into protection mode I suspect because of above, no untoward event like shorted speaker leads;- perhaps it needs disassembly and a dishwasher or thorough clean treatment? But it hasn't been turned on in 5-10 years either, yet also bought new in early 90's. Shame! )
Much to do!
I suppose I'd better get around to posting pics of the current <ahem> system(s) and doing an introduction appropriately at some stage too!
Thanks again, & kind regards;- Ross
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Post by RdM on Apr 5, 2020 21:54:10 GMT 12
Hi Ross RdM - this is my Heathkit Capacitor Checker - Model IT-28...
Ah!
Totally different!
Rather than go through the work of taking a photo, transferring, uploading, getting codes...
May I refer to a quick couple of links? (I have yet to cook a late dinner! ;- )
and this youtube video
(I haven't watched more than a few seconds yet, but it's my model;-)
[Edit:]
Oops!
No, it's not my model, which is in fact labeled exactly "Heathkit R-C Bridge Model C-3U" not a "Heathkit Condenser Checker", - yet - it looks practically identical.
It's been a while since I've been inside it, so I'll have to look and post photos to compare &or confirm either way. But very similar regardless.
That kind of thing.
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Post by RdM on Apr 6, 2020 0:59:34 GMT 12
Addendum:
This is a useful and interesting read, and Owen, your IT-28 is mentioned, discussed, toward the end of the page.
~ RdM
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Post by Owen Y on Apr 6, 2020 20:06:12 GMT 12
Thanks RdM. The calibration instructions will be handy too, if/when I get around to refurbishing it. I am reminded that my Leak Stereo 20 amp is still on its 1967 (53 years old!) filter caps. And I think, unsurprisingly, they are starting to play up a bit.
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