Nothing wrong with doing as you suggest. However, it must be noted that on those old preamps, they probably need some refurbishing, and at least re-capping, to sound anywhere near like they did when they were new. Some of the internal components degrade with age and use, and need to be replaced to approximate original performance.
I might say that an old Yamaha C2 is not giving you anywhere near what is possible today with phono preamps. But it will do the job well enough for you to have some listening enjoyment until you discover what else can do better for you.
I might say that an old Yamaha C2 is not giving you anywhere near what is possible today with phono preamps. But it will do the job well enough for you to have some listening enjoyment until you discover what else can do better for you.