John Greenland
CVRS Member

Hi Ben,
I guess the question is how original did you want to keep the radio ?

For example if you replace the ballast with a 50L6 and add a 330 ohm resistor across the heater you would effectively turn the tube into a 300 ma tube instead of a 150 ma tube.
The resistor would be 7.5 watts and I am sure a 10 watt one would do very well.

If you had the space, two 25L6’s in series would also work without a resistor but you need another tube socket.

Just food for though from my slightly off brain !

Good luck
John G. VO1 CAT