I bought tubes today to retube all of my 6 amps. I bought a couple extra to tinker a little. Ended up getting about 25-27 tubes total. I liked what I was reading about the 5751. I saw somewhere on here where doc says it scoops the mids just a little and gives it more headroom giving it more of a brown deluxe vibe. I believe I got a JAN GE? Hopefully it is worth the money! I did skimp on the EF86. My z28 isn't that old and prob only has 3-4 gigs on it so it's not ready for a tube swap yet. I bought a Electro Harmonics ef86 and 6v6. Anybody ever used these? Just got them for spares for now. Couldn't make myself spend $100 on an Amperex or other brand NOS ef86. Not yet.
I felt that a 5751 gave the Z-28 a more Fender ( Brown face Deluxe ) type tone. More scooped and a bit hollow, but it is almost impossible to find good 5751's at decent prices and large quantities lately. I found the Tung-Sol to be a nice replacement smooth, not brittle with a touch more mid's . I found it very important to limit drive signal to a 6V6 for optimum tone.
Route 66 Z-28 Carmen Ghia MAZ 8 Z-Plus Jetta Z Verb 11 Guitars, 4 cabinets and lots of Pedals(including a Z-Drive)