Hi Jek, The Bendix 6106 electrical specs. are close to the 5y3gt and could be used as a substitute. However,the Bendix is a indirect heated full wave rectifier and the 5y3gt is a directly heated full wave rectifier.Meaning,if you used a directly heated rectifier in your power supply.The other tubes in your pre would recieve a blast of full voltage before they had a chance to warm up and stabilize in the circuit.This blast of voltage would strip the cathode out of your other tubes very quickly on start up......If you are going to try other rectifiers ,make sure test values on both sides are very close or even mirror matched.If not you could get a chugging weird noise out of it.Its also important that the regulators are matched very closely,the regulators work directly with the rectifier.If you buy these tubes from a vender,request matched sides in the rectifier and matched pairs for the regulators,within 1 to 2 MA.would be best.Your ears will appreciate the great 6f6g and 6106 combo.I have afew select n.o.s. mirror matched 6f6gs Im contemplating selling,including a n.o.s.factory 5 pack of Sylvanias that are all perfect matched, all five matched with in 1 MA.of each other......I was on Micks site last night and see his Malbec amps will be available very soon,anyone here going to be the first to order a pair?