In some C+'s it's possible for one of the 1K power supply resistors to go bad, or drift. These are the 2W Metal Oxide ones on the filter caps board. Another known issue is the 1K resistor on the preamp board. This is on the bottom right where the brown wire from the filter cap supply feeds the V1 voltage buss. If either of these have drifted or have gone out your V1 will have higher voltages. With the filter supply drained, see if you can get both resistors in the filter supply to read 1K or so. Also, see if you can get the V1 buss resistor to read 1K and check the value of the two plate load resistors off the V1 buss. They are usually brown Dale metal film, blue metal film or if it's an early one black resistors. The one closest to the 30uf/500V cap on the preamp board should read 150K and the one to the left should read 100K. In some instances the most that would be replaced is the 1K buss resistor with a higher wattage, but some have needed the 2W 1K power supply resistor and the 1K preamp board resistors and possibly in a really bad case both plate load resistors. If you know what your doing or end up taking it to a tech, the V1A plate voltage should be between 240-249V after the 150K resistor. This would be my first measurement to see if I have too much voltage going to the V1 causing it to eat tubes.