Adding rectifier tube - Traynor YBA-1

As the title says, for a 68' YBA-1 what are the limits of the type of rectifier tube that can be added? It's got an extra 5v tap on the original transformer.

I've tried the wire-round resistor in series but it has a weird, non-linear ripple effect with heavy volume and not a lot of sag even at 800ohm.

Meanwhile I have this great 60s Raytheon 5U4, an extra tube socket and some time to install.

I have replaced the cap cans for dual F&T 50/50 a few years ago, I imagine this is at the limits of most rectifier tubes.

I'm currently running KT77s a little under-biased. Very happy with this setup as it gives a little Fender flavor and has fantastic, chimey cleans.

Yeah, the 5u4 should work fine. just unhook the AC HV from the diodes connect them to plates of the 5u4 (pins 4, and 6) hook the 5v to pins 2, and 8. Then pin 8 is your new B+ connect that to where the diodes use to junction at.

you'll drop 40ish volts, so a slight rebias, and done.