There are two steps to finding the Thevenin equivalent circuit: finding the Thevenin voltage and the Thevenin resistance.
Thevenin voltage is the voltage across the two points you interested in (Vin). In this case it is easy to calculate as there is no current flowing in the 43 and 60 \$\Omega\$ resistors thus no voltage drop. Thus the voltage at Vin is the same as the voltage form the source, 72 V.
Thevenin resistance is calculated by 'turning off' all independent current and independent voltage sources and calculating the resistance between the two points. Turning off a voltage source sets the voltage across it to 0, which results in a short (0 \$\Omega\$) in parallel with the 275 \$\Omega\$ resistor. Any resistor combined in parallel with a short results in a short, leaving you with the 43 and 60 \$\Omega\$ resistors now in series, giving a Thevenin resistance of 103 ohms.
Putting the two together gives you a voltage source of 72 V in series with a 103 \$\Omega\$ resistor for you Thevenin equivalent circuit.
My opinion.
Through hole parts are often cylindrical. Hence applying stripes is simple in production. Resistors may have five stripes, tolerance, 3 significant digits, and order of magnitude. That is a lot of information to write, "22811" 22.8ohm 1%? In san-serif font what is 88818? It would be possible to read 1, 2 or 5, 6 or 9, and 8 rotated, i.e. upside down, and be confused.
As pointed out by JRE, a letter in the text is used to help ensure the text is the correct way round, e.g. 22K8.
However, while colour blindness is a problem for stripes, dyslexia is for text. I know of people who would write 'k' backwards without noticing.
Edit: There are many written languages which do not use the Arabic digits (in fact, Arabic digits is a misnomer, because the Arabic digits are different shape or value to commonly recognised digits in 'the west'). So printing digits isn't automatically better than a level of indirection via colour which is language independent.
One pretty thing about 7 of the resistor colour codes is it is in the same sequence as the colours of the rainbow (in some cultures), so many people learn that part of the sequence as children.
The through hole cylindrical part could have its wires bent in any direction, and coloured stripes are still legible from any direction.
If written text is applied in only one location, the part value may be obscured or invisible when it is in circuit. That would be a disaster for repair and inspection.
Hence, written text will have to be applied on all sides in order to be legible, which may well be more difficult and hence expensive to produce, and still awkward to read. Stripes don't suffer from this orientation problem. Stripes are simple to use.
Manufacturers have already invested in machinery to product components with colour stripes.
Where is the competitive advantage? There needs to be 'new' money to fund the change over to printed numbers, or it won't happen. I don't see anyone financial benefit.
I haven't seen any new robots doing pick & place with through hole parts. It is hard to imagine such a robot would have enough financial advantage over SMT to make it worthwhile.
The assembly staff who use the components will have to be retrained, and what benefit does the assembly company get?
Through-hole with printed numbers would have to show big benefits to replace coloured rings. AFAIK, SMT has displaced through-hole in the majority of products; robots are cheaper than labour costs humans for mass production.
"Show me the money" - It seems a very tenuous benefit to printing numbers vs lots of cost, especially when the investment has been made already, in a shrinking sector of industry.
Best Answer
Carbon resistors like what's in your vintage radio are not stable over long time periods. In my experience, the resistance moves upwards. I have noticed this even on early Delco Studebaker solid state car radios that persisted with carbon resistors. Your radio probably has pre-WW2 resistors because WW2 made designers adhere to the preferred range which 250K is not. Due to the age of your radio, I think you should replace all the old resistors. Remember that many small modern resistors do not have the voltage rating. It is good to get the chassis to spec so the valves will all be at their correct bias points.