I have 2 matched Quads of Western Electric 300B's Ive had for years in storage. I bought a Metro GMP45 3-4 months ago. Slightly used < than 20 hours use and less than 1 year old. It already had matched NOS GEC's in it from Metro. I swapped out the Modern Mullard Rectifier with an NOS Mullard 1961 Fat Base and the Modern Mullard 12AX7's for 3 NOS Mullard 10M's with Gold Pins. The New Mullard 12AX7's were so noisy and microphoinc they were unusable and only had 20 hours on them. Now its all but dead quiet. Im wondering if I can use the NOS 300B's ???? In Place of my NOS GEC KT66's in a Metro amp with Heyboer Drake type transformers Metro uses. If its possible I wonder if they will be To HIFI ?????? I know bias would have to be reset.