Princeton Scratch Build

[mainArtery]

I hope I put this in the correct location...

I am scratch building a Fender Princeton replica using Mercury Magnetics, and I have some questions...

I believe the original did not have a center tap on the pt, the Mercury pt does, should i ground that center tap or float it?

I also want to use a EL84 in place of the 6V6GT/A, what changes to the stock schematic will I need to make to accomplish this?

Any help would be greatly appreciated!

[black_labb]

if it has a tube rectifier then the ct would be grounded. no other way to do it with a valve rectifier

[MWJB]

"I also want to use a EL84 in place of the 6V6GT/A, what changes to the stock schematic will I need to make to accomplish this?" Most changes will relate to the PT specs rather than the schematic per se - EL84 draw more heater current than 6V6 so you'll want a PT with more 6.3VAC current capacity than the stock Prinction 2A rating, 4A would be nice.

Typically EL84 are run at less B+ voltage, in fixed bias many current EL84 amps run around 330vdc on the plates (<270-0-270VAC at the PT B+ secondary).

You'll want less negative voltage from the negative bias supply voltage divider, aim for approx -14 to -15vdc, prior to installing tubes and fine tuning plate current in mA (30mA per tube). May be simpler to source a PT with a dedicated bias tap and base the bias supply on a current amp like Fender Pro Jr?

[Bruce / Mission Amps]

I hope I put this in the correct location...

I am scratch building a Fender Princeton replica using Mercury Magnetics, and I have some questions...

I believe the original did not have a center tap on the pt, the Mercury pt does, should i ground that center tap or float it?

I also want to use a EL84 in place of the 6V6GT/A, what changes to the stock schematic will I need to make to accomplish this?

Any help would be greatly appreciated!

The stock preamp stages will have so much gain it will turn the EL84 inside out.
It only needs about 9vac to 12vac of signal at it's grid to turn on full blast.
You'll need some kind of resistor divider after the first (and maybe the second) preamp stage to lower the amplified signal output by about 35%-40%... or maybe more, but at the same time not change the tone of the preamp.
I'm thinking the CT you are referring to is the 6.3v filament supply.
Do not use it if you are wiring the sockets like an original where one filament wire is grounded to the chassis.
It would be better to use black face Champ socket layout for this though and ground the filament center tap... either at the chassis or the positive end of the power tube's cathode biasing resistor.