Those are likely multi-section electrolytics in the cardboard cans. I see some are also mounted on phenolic wafers, too, and from a look at the backside pic it appears that they may be isolated from ground. In case you don't know (and not being a tube guy you may not), the outer can on the multi-section electrolytics is typically connected to the negative side of the cap. In cases where the negative side cannot connect to ground, they're mounted using insulating spacers, and often covered with cardboard tubes (as you have here), or shrink tubing and an insulating cap on the top (as they are on some old HP stuff I have worked on).
You'll note that there are symbols near the terminals (a square, circle, triangle, 'D' shape, etc.), and on the side of the cap (may or may not be on the cardboard; if not it should be embossed into the aluminum can under the cardboard) there will be a list of the symbols, along with the associated cap section value - for instance, D 40UF 250V, (square shape) 30UF 350V, (triangle shape) 10UF 400V would be a 3 section cap, common negative, with a 40uF, 250V cap; a 30uF, 350V cap and a 10uF, 400V cap inside, connected to the terminals as indicated. They can have multiple values, and differing voltage ratings all within the same body.
It takes some effort, but they can be restuffed with a bit of patience and a few tools. Modern electrolytics are often MUCH smaller physically for a similar value, and one or more of them as needed can be put in the can after the original guts have been removed. As it appears you've discovered from your online searching, there are several methods used to restuff them - some cut the can and epoxy it back together (which may be a good option for you as yours have the cardboard covers which should hide the cut); others undo the crimp at the bottom to remove the guts, then re form it with a tack hammer or the like, I prefer the latter method, though it's time consuming.
I've done a few single section ones for an old HP DVM; here are some of the pics of the process:
Initial opening of crimp with knife blade:
Continuing to open the crimp with a small screwdriver (a small electronics vise is a big help during this process; doing it holding the cap in your hand is just begging to stab yourself, repeatedly!):
Once the crimp is fully undone, things can be pulled out:
I used a heat gun to soften the tar holding what remained of the dried out cap in the can and then pulled it out; the softened tar can be dug out with a pick if necessary to make room for the new replacement caps:
The new cap's leads are formed and soldered to the terminal:
The negative lead is brought out and soldered to the mounting ring:
And finally the crimp is re formed by gently tapping it back down as you work around the perimeter, using a small hammer. The cap is shown in the vise for the photo because that's where the camera was set up and focused on, but when redoing the crimp the back end is rested on the table to prevent movement from absorbing all the force of the tapping without the metal moving. I actually rest it on the table and nest it against the heavy cast iron base of the vise, and tap at about a 45 degree angle at first to form the metal around the mounting ring and get it tight. The blows are shifted to be more parallel to the face of the cap as the metal folds down. Use very light hammer taps, rotating the cap slightly between each one to evenly re form the metal. Take your time with this step and it will fold back down nicely:
The hammered part of the crimp will look a bit buggered up, but it is not visible when the cap is mounted, and I prefer this to cutting the can in a visible place.
There are a few more photos of the process at:
https://pmanning.smugmug.com/Electronics/Restuffing-can-electrolytics/51169977_mDp2vM#!i=4261375442&k=QLmNcB2At some point when I do another I'll make a better step-by-step sequence, and do it on a multi-section cap rather than the single section one shown here.
-Pat
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