For our OP I sketched over the schematic using conventional current the direction DC flows from B+ through the circuit and returns to ground. The 5AQ5 being self (cathode) biased sets the tubes quiescent current. Under normal operation there should be no DC flowing in the volume control or grid circuit. C50 is the grid coupling cap that's purpose it to isolate the 5AQ5 grid from the preceding plate circuit's DC. C51 basically damps out very high frequencies in the output trans primary. It's this flow of quiescent DC current that produces the appropriate voltage drops across the resistance or impedance of the various components. Healthy capacitors should not pass DC therefore would not change this quiescent or idling current in the circuit. You could remove C50 and 51 and the circuit should still work completely isolated from the rest the TV. Normally if you touch a screwdriver or finger to the grid or volume control it will produce a buzz in the speaker. Anyhow I though it might help remove some of the mystery surrounding how this little section of the TV works. Once you understand what's suppose to happen it sometimes helps to find the source of trouble.
