Hello Everyone,
I have a Knight radio that I cannot identify. It has a wooden cabinet and is Am/Shortwave (7.0-2.2 MC). The tube lineup is: 25L6, 25Z6, 6K7, 6A8, 6Q7 and one more metal tube with no identity. Any ideas?

The tube with no identity is the ballast tube. If it's open, there will be no voltage to the tube heaters. If your set has a dial lamp, there is a tap inside the ballast tube for that as well.

:The tube with no identity is the ballast tube. If it's open, there will be no voltage to the tube heaters. If your set has a dial lamp, there is a tap inside the ballast tube for that as well.
:It does have a dial lamp. It lights up for a second and goes out. You're right, the tube heaters do not operate. Without a schematic, what would be a good guess for the ballast tube?

Don't know what a direct replacement ballast tube would be. The way the pins are wired. What is better to do in this case, is to make a capacitor ballast. You can lift the can of the tube from the base. Check how the AC line is wired from the line cord to the first pin in the heater string. Use an 8.2 Mfd @ 160 VAC capacitor in series with the the heater sting. the capacitor will fit in the old ballast tube can. Here is a link showing this. scroll down the page a little.

http://www.oldradiosrus.com/build.html

Now for the dial lamp. Lift the last tubes heater in the string going to ground. Wire in a #44 dial lamp in series from the last tube heater to ground. Add a 47 ohm 1 watt resistor across the lamp (shunt) This works good.

The tube with no identity is the ballast tube. If it's open, there will be no voltage to the tube heaters. If your set has a dial lamp, there is a tap inside the ballast tube for that as well.