I recently designed a tube moving coil preamp PCB, and I used solid ground pours (not "hatched"), top and bottom. To budget effect I used 2-layer, but 4-layer would have included heater traces, now twisted wires. Throwing caution to the wind I also used a cheap SMPS, which had some not-so-nice high frequency artifacts needed to be sorted out with uH and nF filters.
As the tubes are VHF pentodes and triodes, capacitive loading would be a bonus, and a max 47K input would not be much upset by a couple of pF board traces. Even a MM would need some pF. MC transformer stepped up use ~ 22K load.
The board is attached to an aluminum plate, with many threaded AL standoffs to grounded PCB vias, and the plate is attached with a single screw to the outer case. That plate provides a heatsink for conduction cooling fullpak-TO220 HV MOSFETs. Ground loops has not been an issue. RIAA filter shaves off gain 40dB from 20Hz to 20KHz anyway, and continues way beyond that, so HF roll-off here is a bonus. I'm not looking for MHz performance.
Vintage electronics typically use "star ground", or a "bus wire", as ground planes were not an option in the point-to-point wiring era.
I'm planning to use a 1-sided aluminum PCB for an all SMT design, as it provides a heat sink for my constant current plate loads.
Via sizes, and ground-pour distance to traces can be well specified, controlling capacitive loading a little. Using 1.6mm thick PCB reduces capacitive load, compared to 4-layer where I typically would use a 0.2mm or 0.1mm thick dielectric in RF circuits.
Yes, all solid ground planes worked OK for a tube preamp.
They need Geritol.
