old thread

[rp]

Your coming full circle which is good, build it stock, then mod is a lesson learned. A 12AU7 is not a drop in substitute for a 12AX7 and a waste of time IMO and (neither is a 12AT7) the proper subs here are 5751 and 12AY7 and unfortunately old ones over the modern ones. Luckily, while I think most tweeds benefit from 12AY7s as originally spec'd the 5F1 should keep the 12AX7 as originally intended. The bypass cap on V1a while not on the schematic was on the production models and not an option IMO so no switch needed, choosing btwn .68 - 25mf is up to you. Putting a cap on V1b is a mistake but feel free to try. Fender tried to keep their amps clean but not here, he let this little fucker go balls out, Leo had it together.

An other tip 4U, IME don't stray far above 470 ohms on the cathode resistor. These amps were meant to run hot, if you're red plating then try different 6V6s, above 600 ohms it really kills the sound, and I think even 600 is too high. Just run it hot. Hopefully you'll get 360-380V on the plate, that's the sweet spot, and you'll be fine with 470.

You can really hear the tube rolling in a Champ, but nothing will make it much brighter. I found '80s JAN Phillips 12AX7 a tiny touch brighter than many others, but also harsher. I actually like the coin base GE 6V6s in my 5F1s. I'm not too familiar with current tubes.

There, now you know everything I know.

[utervo]

Your coming full circle which is good, build it stock, then mod is a lesson learned. A 12AU7 is not a drop in substitute for a 12AX7 and a waste of time IMO and (neither is a 12AT7) the proper subs here are 5751 and 12AY7 and unfortunately old ones over the modern ones. Luckily, while I think most tweeds benefit from 12AY7s as originally spec'd the 5F1 should keep the 12AX7 as originally intended. The bypass cap on V1a while not on the schematic was on the production models and not an option IMO so no switch needed, choosing btwn .68 - 25mf is up to you. Putting a cap on V1b is a mistake but feel free to try. Fender tried to keep their amps clean but not here, he let this little fucker go balls out, Leo had it together.

I actually mistaked my ECC82's as 12AY7's!

Planned on doing it like the schematic I posted, with 5E3 preamp.