Here’s a summary of the work I performed on the Citation V, also a few photos.
1. All the internal wiring including the input coax was sticky and “greening.” This was the result of the amplifier being made in an era in which a lot of PVC insulated wire was manufactured with a defective plasticiser. I stripped it all out and replaced it with new high quality wire from AES.
2. I replaced all the tube sockets with exact-fit NOS. This made the wiring job somewhat easier, because I didn’t have to remove the wires from the sockets. I just removed the sockets with the wires attached and tossed it all in the trash.
3. I installed a 3-wire line cord for safety. The green earth ground wire is soldered to the chassis at the rear.
4. The 3.3Ω output tube cathode resistors had all drifted off value. I replaced them with 1% parts.
5. I installed Jim McShane’s power supply kit, including the optional screen choke.
6. I added a short ground bus on the power supply bracket to act as a star ground. I insulated this from the chassis to eliminate the possibility of creating a ground loop with other equipment. No grounds are connected to the chassis except the green AC earth wire.
7. The plastic cover on the rear of the Balance meter was missing. I made measurements and cut a new one from .020” FR4 using a CNC mill.
8. I replaced the aging NFB phase advance caps with 68pF silver mica, and I replaced the 220pF caps in the step networks with 240pF polystyrene.
9. I installed a 270Ω stopper at each output tube screen.
10. I replaced all the coupling caps with new parts that I had on hand (Jim McShane also sells these in a kit). I increased the value of the screen bypass caps at V1 and V5 from 0.47uf to 1uF (suggested by Jim McShane).
11. A previous owner had removed the 1Ω filament resistors and terminal strips at V1 and V5. I installed original type terminal strips and new resistors.
12. The Citation V has a DC balance adjustment, but no adjustment for overall bias current. I selected a value for R50 in the power supply to set the output tubes at approximately 44mA to 45mA each. B+ in this amplifier is approximately +480V, so the tubes idle at roughly 22W dissipation, including screens. Each screen draws about 1.2mA at idle based on the voltage measured across the stoppers.
13. I installed NOS driver tubes and a matched quad of 6P3S-E outputs. After DC balance was set at both channels, I adjusted AC balance using a spectrum analyzer. The Citation V also has a procedure in the owner’s manual for accomplishing this without the need for special equipment.
I think that’s about it. It’s a truly excellent amplifier, and I consider it one of the best ever made. Hope this information is helpful in your work.
Jack
