Inpepinnovations,,,That was what we called the extra gain stage that went in front of the preamp when using a MC pickup. Nowadays it is no great feat to provide sufficient gain for MC pickups without additional stages. And I don't think they had any gain control (that was in the preamp).
Dean_fuller...If your pickup yields sufficient volume when the power amp is fed directly from the phono stage there is no need for extra gain, which you will just "throw away" using the volume control pot.