I’ve run a handful of checks on a 75‑Ω RG‑59 run versus a 50‑Ω RG‑6 to the same 50‑Ω‑impedance preamp. The 75‑Ω line shows a cleaner phase slope above 40 kHz, especially on a long run; the 50‑Ω line starts to roll off around 45 kHz, with a ~2°‑3° phase lag at 60 kHz. The preamp’s 10‑kΩ input is so high that the 50‑Ω cable’s characteristic impedance hardly matters for voltage transfer, but for preserving the micro‑delays that a clean reverb tail relies on, the 75‑Ω line is a step up. If you’re measuring with a 1 m scope probe, keep the probe tip grounded to avoid adding extra capacitance. Bottom line: stick with 75‑Ω if you’re chasing razor‑sharp high‑frequency phase.

Yeah, that’s the main stretch that matters for the tail. The next hop that trips the phase is the preamp’s own input stage – the little 10‑kΩ resistor and the coupling capacitor; if you push the 60 kHz into that pair you’ll get a tiny lag. The EQ sections, especially those 50‑Hz‑band high‑pass filters, also throw a wedge at the high‑frequency phase if you’re not careful. And don’t forget the speaker cable – a 25‑ft 2‑way with a 70‑Ω characteristic will start to smear the echo if you run it at 60 kHz. Keep every link clean and match the impedances as close as you can, and the reverb tail will stay crisp.

Maybe double‑check the shield grounding on the RG‑59. A poor shield‑to‑ground connection can cause micro‑hum that shows up as a phase wobble at the tail. And keep an eye on the preamp’s bias point; if you drift a few millivolts off the sweet spot, the high‑frequency linearity can degrade. Finally, when you add a 1 kΩ series resistor to a 50‑Ω line, remember it will raise the effective input impedance for the preamp, so you might want a slightly higher bias resistor to keep the voltage division correct. Those little tweaks keep the phase tight.