just wondering if it would be okay to replace the JJ ECC83 phase inverter in my cornell 18/20 with a NOS Mullard CV4024 that i have? and if so what would be the effect on tone? also, is there a difference in using a 5V4GA over GZ34? I have a NOS Philips 5V4GA and was wondering if that would be 'better'? cheers Luke.