you probably have to resize your image(s) due to the size limitation. The maximum allowed size for attachments is 180kB. You can use Paint or IrfanView for example to resize your image(s).
If you have to German Version of the Grundig K2 or Musikgerät 1070, then you can find a fitting schematic here: https://nvhrbiblio.nl/schema/Grundig_1070.pdf
In the schematic you can see that the resistor R38 is connected in series to a 50µF capacitor, which is probably the big cylindrical capacitor mounted on the chassis. In most cases, this part contains two capacitors in one housing, but you can replace this part with two individual capacitors with the same ratings.
Maybe the capacitor is faulty and you need to replace it. Before you turn on the unit, you should check if R38 is still 1,3kOhms.
If that doesn't solve the problem, you should check R37, R31 and R14 and the circuit which comes after them. R38 ist also connected to the EL84, but I'm not sure if the EL84 can cause such a problem. Maybe a more experienced person can answer that question.