Greetings & Welcome to AC

Likely you'll find the pre tubes are Sovtek 6N1Ps, which were Frank's standard OEM at the time. The recommended upgrade from those is the 6922 line of tubes. Recently replaced those my self in both my Ultra EC preamp and Ultra DAC. Frank's current stock 6922 is the E-H at $32 each. Lots of options both new & NOS available.
Yes, the flickering light switch is not that unusual over time. To my knowledge doesn't have any effect on the sound. Had the same issue with my T-8 pre, Frank replaced the switch when I upgraded that chassis to the CF line. As to the indicator light next to the switch, you might ask Frank about that. I don't think mine has ever lit up. It may have been a holdover from before he used lighted switches, and would have had a bulb behind it. Happy listening.
