Old metal cap cans

[dude]

I have at least 20 old Mallory cans, they all check out good with readings, within 20%.  They all haven’t had voltage in many years most likely. Is it worth trying to bring up the voltage slowly or toss them...? With prices being $25 to $35 a can, l’m wondering..?

[HotBluePlates]

... Is it worth trying to bring up the voltage slowly or toss them...? ...

Hard to say.

I just got a Sencore LC75 and tested a few caps, including a handful of electrolytics I replaced in a 1964 AC30.  After giving the caps a minute or so to re-form, the originals had leakage (at 400v) and ESR as low as most modern electrolytics.  So I found those particular original 1964 caps (Bianchi & TCC brands) could really go back into the AC30.

But testing for value alone won't get you there.  You could use a Conductance scale if your DMM has one to test for leakage, though you won't be quite as-sure the cap will stand up to higher voltage, or is completely re-formed.

Ironically, the only cap I've had test "bad" so far was an expensive paper-in-oil type I got many years ago.  It tested bad for leakage with both the DMM and Sencore.

[Latole]

I use Heatkit IT-28 capacitor checker, it do a good job

[dude]

I don’t have the equipment to test satisfactory, or a variact either. Perhaps it might be worth taking them to someone who has the correct testing equipment.
Thanks

[Latole]

You can use lamp bulb current limiter.