We have used 100K in the Repro, because that has worked well with the extended response tape head from Flux Magnetics. However, unlike phono preamps, there is no real standard for tape heads. The circuit will work fine with any value below 500K, so you can substitute whatever works best with your tape machine. In the early days, we used 250K or even 500K adjustable trimmers, but a single resistor is going to be more reliable and quieter.
I do show 47K in the schematics for all Eros variants. But I've always expected that builders would substitute if they wanted a different value, or a better quality resistor.
