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Here's something that might work. It uses a Zener, a Darlington pair, and some LED's, with a low ohm ballast resistor for the LED's and a couple pulldown resistors. The one on the left is negative ground; the one on the right is positive ground. The NG uses NPN, the PG uses PNP, but other than that, the parts are the same, with just the diode orientations swapped.

In this example I am using a 1.2V Zener but the Zener value and ballast resistor value will depend on the exact circuit characteristics, which I do not yet know.

Try it yourself:https://www.falstad.com/circuit/ and load the attachment (unzip first).

Edit: the attachment is not working. Paste the following into a text file and load it:

ZIP files can't be uploaded here but the text worked fine for the simulation. Interesting designs with easy to test 10 to 100 ohm sender adjustment! Out of curiosity, are the 5v instrument regulators accurate and consistent?

I honestly don't know. I would assume it would have to be fairly consistent for the gauges to be steady. If not, you can replace the guts with a solid state linear regulator for only a couple dollars in parts. Example here:https://squarebirds.org/Electrical/CVR/SolidStateRetrofit/

Pretty sure you can also get solid state ones already in the case too.

From what I gather the solid state type is readily available premade. I'm not sure how closely they physically match those used in Packards as I've really never paid any attention to them before. The solid state type that I saw had a single mounting tab on the side.

The original 5v regulators are thermal and put out a square wave that is somewhere in the vicinity of 5v so it would be interesting to see how the instruments behave with a closer, more stable voltage.

I just got done re-capping my radio. Seems to work well, though I plan on getting it aligned and the tubes tested. I don’t have any particular desire to buy a signal generator and tube tester for this one use.

It’s well known that capacitors have gotten better in the past 70 years, but the biggest difference was between these 0.47 microfarad 100V caps. Hard to believe they are the same electrically! But I double-checked. These are C16 and C17 on the 472046 (55 Clipper) radio by the way.

I decided to test the capacitance of the paper caps. The capacitor number is followed by the rated μF value (±10% tolerance) then the actual value. As you can see, all the capacitors are defective but interestingly they are above their rated value.
C17 0.47, 0.772
C16 0.47, 2.97
C5 0.05, 0.11
C15 0.007, 0.012
C12 0.1, 0.308
C10 0.002, 0.0032
C8 0.01, 0.017
C11 0.003, 0.0052
C2 0.05, 0.19

I also tested the triple electrolytic, which had values of 30, 32, and 33 μF (supposed to be 20 for all).

To be honest, since all the capacitors seemed to be gaining capacitance, probably the set would have worked fine, but there's not much of a way to be sure of that without testing them. In addition, excessive capacitance in capacitors like C10 and C11 could cause weak treble response, especially at low listening volumes. It's also possible the caps were failing in other ways, for example having an excessive ESR. I don't have a fancy capacitor tester so can't test for this.

The situation is somewhat analogous to firing up an old engine on something like 20W50 oil. It's reasonable to expect that you would have high oil pressure, but you have to trust/assume that the oil pump even works! Until you inspect the pump and hook up an oil gauge, there's no way to be certain that you will have what you may expect. Likewise, even though our capacitors held at least their rated capacitance, there's no guarantee that they would have without testing them, and the excess capacitance is not necessarily preferable. In many of the applications, the design capacitance is optimal. And to be clear, just the process to test the caps in situ is nearly the same difficulty to just replace them.

The cost of the replacement caps was around $30 including shipping but I ordered more than I needed so I had some spares for mistakes or future projects. Needed to replace the RF amp tube also, about $10.

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Interesting that the capacitance had increased with age and use. Can you please post a photo of what it looks like with the modern tiny ones installed? Incidentally, I had a look a few days ago and see that places sell some of the vintage style capacitors too.

By the way, in case anyone is curious, here is a thread on the antique radio forum discussing replacement of paper caps.

https://www.antiqueradios.com/forums/viewtopic.php?f=19&t=220704

How difficult is it to repair this tube on the intake? Fortunately this one seems fine, but I have another which is damaged from rust.

The long external tube should just be a snug fit 1/4" steel or copper tube with about 1/2" of the end simply pushed into the larger heat tube in the manifold. If the heat tube in the manifold is rusted out, that is pressed in and will need to be removed and a new tube pressed in to replace it. As I recall the end of that tube sticks out below the manifold a small amount and end of tube is sort of crimped in several places around the circumference to provide a small opening to act as an orifice to slow air being pulled thru the tube so it can be properly heated as it goes thru. I don't know if new ones can be found at our vendors but believe others have been able to replace them with appropriate sized stainless tubing bought from McMaster-Carr or the like.