Fender Pro Reverb UltraLinear (70w)

[M Fowler]

I would just order from TAD to get the most accurate OT available and TAD are good to work with I've ordered parts from them before.

20% UL per specs.

[gui_tarzan]

I have too, I wasn't disappointed with them at all. I'm still looking at some of the new transformers I got recently from Heyboer to see if any of them might work. The hardest part is the mounting holes, with the extra parts inside this chassis there is almost no room to put a different trans in it without drilling a whole new set of holes.

[pdf64]

I wonder why TAD have selected 20% (assume of voltage) taps?
The Fender OTs are generally thought to have their taps at 12.5%; the OT in my Fender 75 comes out at that, with a 4k4 primary.
These amps may have been designed around the Sylvania STR387 6L6 variant, and regular 6L6GC in the amp may not have a good operational life / facilitate the specified performance.

[gui_tarzan]

So how can a pair of 6L6s put out 45w with a standard OT and 70w with an ultra-linear? I'm missing something here. The standard config uses power to the grids from the power rail, the UL gets the grid power from the OT. Or is there something else going on in the UL transformer that I'm not understanding?

[martin manning]

It's the 500V on the plates and screens, with a relatively small distributed load fraction.