OT Proximity to Preamp..?

[tdvt]

I am working on a small SE amp a friend built a few years ago & never quite finished. The layout was somewhat discombobulated, so I am stripping things back to try to reorganize things.

To that end, I was hoping to mount the transformers closer together, leaving a nice quiet area for the front-end (just 1-12AY7 w/vol & tone)

But moving the OT closer to the PT-end does not pass the headphone test, hum increases quite a bit.

The quietest spot for the OT is on the verge of being under the pre-amp, on the other side of the chassis sheet metal.

So the question is how much hum/noise does the OT create in regards to the preamp's sensitivity? 

[shooter]

SE amps by their nature have NO "hum cancellation" that you get from PP designs


how much is annoying, users choice. 
the OT is a MASIVE signal compared to 1st stage preamp, inductive coupling is a square distance math problem i believe.
I've mounted OT's on the back of chassis, hanging upside down under chassis, both worked fine.
you want to take it out of the same "plane" the preamp tube is in for better de-coupling.
if you're suck in the same dimension, distance, lead dress, shielding all come in handy

[tdvt]

you want to take it out of the same "plane"

Thanks for the reply.


I went back with the headphones to try one more thing after posting this & got what seems like it would be an Amp Building-101 lesson about power transformers, their fields & orientation. Maybe others are already aware of this, but I had no idea.


First round, the PT (Fender-style lay-down) was mounted how I got it, with the shorter sides (w/the copper foil) facing the front & back of the chassis.  So I pulled the PT & spinning the PT 90° eliminated the hum I was hearing in the headphones.

When I looked at all the Fenders that I have, they were all mounted with the long sides facing the front & back of the chassis.

I am guessing that having the copper foil short sides, which I assume is some sort of shielding, facing down the length of the chassis should have been a clue.

The way it came, the PT field was still radiating down the chassis no matter which way the OT was spun, a losing battle.


Anyway, much better & I now have room to keep things further apart.