So, your Tek 7A26 stopped working.

As with the Tek 7904 itself, this is a decent piece of equipment, but it's decades old and suffering from that. They include a large number of tantalum caps and these, as with the 7904, have two rather spectacular failure modes. In my case, the 10uF 25V tantalum (C1018) on the -15V supply rail dead shorted, and given that it's fed by a custom RFC (LR1014) that's not particularly heavy duty, the capacitor/shunt shrugged and the RFC let the smoke out instead. That's not exactly the outcome I would have wanted, given that the RFC (part number 108-0184-00 and NLA for decades) is impossible to find either specs or stock of. The parts breakdown in the 7A26 service manual only lists "COIL,RF:3.2uH(WOUND ON A 10 OHM RES" which is enough to get started but not really enough to produce this part yourself. I googled for a while and found many other people with this problem, but no info on the number of turns, resistor wattage, diameter, magnet wire gauge... the list goes on. So I ended up carefully picking my charred RFC apart (luckily I caught it before it actually melted the wire through...) and measured what was left. The resistor is a 1/2 watt 10 ohm carbon composition unit and an Ohmite OF100JE appears to be a good fit dimensionally. The choke portion is 45 turns of what appears to be #34 magnet wire (I have not measured the wire exactly, just eyeballed it next to what I had on the shelf) close-wound in a single layer and a run through the coil inductance calculator for sanity-checking indicates that this should give us approximately 4.22uH, "close enough" (and better than!) the original for me to be comfortable.

since there are something like ten of those 10uF 25V tantalums on the board and they're all around the same age, I decided to do a tantalum-ectomy and replace all of them with AVX TAP106K035CRW at 66 cents each. I'd rather pay for all of them than have to buy ten more resistors (they're actually more expensive... will wonders never cease) and fiddle around with winding RFCs on them.

Addendum early 2021: The replacement RFC winding and installation went smoothly and the 7A26 lives again!