Power Transformer As A Choke or Power Transformer as NFB?

I have a number of small power supply transformers laying around, and I've been using a PSU layout similar to the G7 for my tube preamps.

Can I use a power transformer (IE a cheap 120:9VAC) as a choke for my B+, or do these things fry at 120V DC?

Would it be worth it to take a DC blocking cap to the primary and try to reverse the phase of the remaining PSU ripple to feed it into the output stage?

I've seen some instances where the PSU ripple is fed into the signal after the first plate via high resistance & capacitor. Perhaps this is a better way of further reducing PSU noise?

My noise floor is about -70dB right now, I'd like to get rid of a few more DB of that PSU noise.

http://www.gyraf.dk/gy_pd/g7/gic_s.gif

That gets done all the time.
Use a high fidelity output transformer for a hi fi choke.
Or if its git amp, any ol pwr trans ought to work.

Just leave the secondary open, or burden it to fine tune the inductance.