The QB5/1750 has the same socket as 4-1000 / 3-1000Z = super giant the pins are a little bit bigger in diameter, so the Eimac-Sockets have to be modified a little Original Valvo sockets are still available in Germany at "Schuricht" for about 90€ 73 de Peter, DF3KV ( homebrew 3x QB5/1750 )