[morzh]

OK. This is a simple matter and I always prefer teaching fishing vs giving a fish.

And I am not sure why you are saying why they are for total of 1.5 Amp when these are usually in series.
Do you want to quickly learn how to do it?

If yes, please give the radio model.

Meantime, the first attempt.

Sum up all the voltages of your tubes.

25 +25+6.3*3 = 68.9V

Now you have 120V.

You thus need to drop 120 - 68.9 = 51.1V

Your current is 0.3A.

Therefore your resistor is the voltage you need to drop divided by the current which is:

51.1/0.3 = 170.3 Ohm
Which is pretty much what Rod got for you.





Now. I suggest you calculate the power.  Which is either 51.1V-squared divided by 170.3 Ohm which is 15.3W, or, which is the same,  51.1V times 0.3A. Also 15.3W. Pick the one you like.

In order to be able to dissipate this much and not to smoke anything you will need at least 30W resistor, which, especially under the chassis, will generate a lot of heat.
I suggest you use a capacitor instead.
Again, if interested. Just yesterday someone gave links to those calculators (I do it by hand).