Reforming caps?

[nuke]

Definitely a fresh, new electrolytic, within a year of its manufacture is the best.

I have to say though, outside of a manufacturing site, that is often hard to accomplish. Parts I order from the big electronics suppliers are often a year or older. Part of the downside of buying small numbers. Where I’ve worked, ordering tens of thousands of components or even more, means you usually get stuff right off the supplier’s production line.

Ordering 10 units means you get the end lots and the sweeps off factory lines.

Fortunately that generally works out most of the time.

[Roe]

normally a 100k resistor before the cap works well

[TUBEDUDE]

All solid reasoning for eliminating electrolytics in builds, and replacing them in old amps as room permits.
Unless I have to use a very small footprint for a feature rich grab 'n go combo, I use metalized films for the power supplies.
This months build, Voxy Lady, is based on an old Vox AC-10. It's so simple there's room for the MF caps in a 13"x7" chassis (small for PTP).

[Phil_S]

Go browse eBay for a used electrophoresis power supply. Cheap as dirt, adjustable, regulated 0-500VDC power supply, plenty of current. Most are not particularly clean for powering an audio amplifier, but they are plenty good for testing capacitors at voltage and applying a re-forming voltage with voltage and current control.

Something like this? https://www.ebay.com/itm/356569191158 I am not familiar with this thing. It it as simple as dialing in 5mA and attaching it to the rig shown in Figure 1 of the PDF posted by RG? If using this regulated power supply, I can omit the ammeter from the rig?
You've gotta love DOD for thinking of everything. LOL, the example given is for 50 caps. Thanks for posting, RG!
I didn't expect such a robust discussion to emerge. So much to know... what a treasure TAG is.

[HoodooVibes]

Interesting and valuable information presented here, thank you.

Tested a setup using my inexpensive Amazon Megger powered by 9v battery. At 250vdc it supplies 2.5ma into a random 33uf/459vdc electrolytic. No need for a lamp protection regulator. Just have to make it variable to reform out of circuit capacitors. The unit is capable of 250/500/1000 VDC.

[nuke]

Something like this? https://www.ebay.com/itm/356569191158 I am not familiar with this thing. It it as simple as dialing in 5mA and attaching it to the rig shown in Figure 1 of the PDF posted by RG? If using this regulated power supply, I can omit the ammeter from the rig?
You've gotta love DOD for thinking of everything. LOL, the example given is for 50 caps. Thanks for posting, RG!
I didn't expect such a robust discussion to emerge. So much to know... what a treasure TAG is.

I scored a slightly fancier one with two analog meters on the front panel, and knobs for voltage and current control, so it can run in constant voltage or constant current mode. The internal electronics are all simple analog op-amps and easy to figure out.

The way it works is pretty simple: The voltage/current settings control a UJT oscillator (uni-junction transistor, blast from the past!) and the duty cycle of that. That feeds a small pulse transformer, which controls two SCRs at their gates. The SCR's are wired back-to-back and "slice" the incoming 120vac mains sine wave. That then feeds are large step-up transformer. It works kinda like a light dimmer, the more of the cycle that's conducted, the more voltage comes out of the step up. That's rectified and filtered. Too dirty due to the SCR's chopping the AC waveform up, but more than good enough for cap testing and some other interesting things.

I'd probably avoid the later, fancier ones with microprocessors and switch mode power supplies, since they're probably harder to figure out or mess with.

It might take some reading, there are lots and lots of them on the used market. Some are only up to 250v, some are up to 4000v. The one I got is up to 500v. They do offer whopping amounts of current, and there are some safety things to figure out on them.

I think I paid $49 a number of years ago.

Handle it with gloves and clean it thoroughly when you get it. Some of the chemicals used in DNA labs are scary, and designed to mess with DNA molecules.

(I was involved in molecular cytogenetics analysis instrument R&D many years ago...)