military phone question

[Bill Mc]

Hello, was sent over by someone at antique radio forum.  Did not know there was this much interest in phones.  I have a 302 in service in a spare bedroom and several magneto phones hooked between house and some farm buildings.  Most of my lines are underground.  My question is about a TA-838TT military phone.  Works OK but has a small hum that sounds like unbalanced line.  Can anyone help with this?  It's not dial, so I hope it's OK to ask here.  Thanks, Bill

[BDM]

Is this connected to your private line, or is it connected to the main house line? Does it have a schematic?

Would this be it?
http://www.prc68.com/I/TA838.shtml

[Bill Mc]

BDM, Thats the one.  I have been unable to find the schematic.  They are made by Star Dynamic and North Electric.  It has an "electronic magneto" and will not work with the other old magneto types.  I have it on POTS, and it's OK except for the hum.  I have another just like it and it is OK.  I was hoping hum would be a common enough problem that someone could help.  So far what I see on the net is very incomplete parts of manual.  Thanks, Bill