tube echoplex EP2 low hum help!

[revbrodiddley]

Hi everyone.
I have an EP2 that sounds amazing. I actually have two EP2's and one EP3 and this one is by far the best sounding of the three. However, there is a low hum that increases when the volume of the echo is increased that makes the echo pretty much unusable for recording purposes and almost unusable for live use. Are there any things I can do to track the problem down and fix it? All the echoplex repair guys I know of cost a freaking fortune. I am a very novice tech sort of person but am very willing to be patient and learn how to fix this!

the unit currently has the original two prong plug. I was thinking about putting in a 3 prong as it could just be a grounding issue? I can post videos on youtube if that'll help anyone diagnose. Thanks in advance for any help!!

-Bro