1. Line cord with ballast resistor
The so called hot tail radios had a ballast resistor ( 3rd wire) in the line cord that was used to reduce the voltage for the filament chain. In this case there were 4 tubes with 6.3 volts/ 0.3 amps all in one row. (See schematic - external link)
The problem is that these line cables are running hot and the insulation becomes brittle in most cases. As replacement nice and save new cloth insulated cables are still available but -  I do not know any source for these special 3 wire cable ( incl. resistor wire).
The 4 tubes need = 4 x 6.3 volts = 25.2 volts. The difference of 90  volts ( 115 minus 25) to be consumed in the ballast resistor. That would result in an additional heater source in the cabinet of  90V x 0.3 amps = 27 watts - which is too much in most small sets.
Therefore I tried to find another solution that
1. works with a low internal heater consuption
2. looks original

The tiny silicon diode inside the mains plug reduces the mains voltage to half (50-55 V) without reducing the plate voltage when working in the same direction as the rectifier tube. Thus we have only approx. 30 "useless" volts that are consumed by an additional 10 ohms/ 10 watts resistor under the chassis
Let me know what you mean about this solution. Do you have other/ better ideas??
 

2. Smoothing Capacitor Block
There is a  smoothing electrolytic capacitor ( 2 sections) inside a cardboard box installed at the speaker board. I opened this  cardboard box, took out the old capacitor rolls and refilled with a new electrolytic capacitors. For the connection I used the old cloth isolated wires. Thus nothing is visible above or under the chassis.

3. Discrete capacitors in cardboard tubelets
There were 2 capacitors out of tolerance. I refilled these caps as described on my Volksempfänger page.