I received two transformers yesterday from UPS.  XPWR051-120 and GXSE15-8-5K.

I've been waiting to get the transformers placed before drilling the chassis.  Last night, with all secondaries taped off for both transformers, and headphones connected to the 8 ohm OT secondary, I applied 120V to the PT.

The PT buzzes in my hand, and it is amplified when set on the top of the chassis.  I moved the PT and OT around to find placement for no hum, and I find some amount of hum in the headphones anywhere on the chassis, and much louder as the two get closer together.  I decided on placement furthest apart on opposite corners, laminations perpendicular.

I have yet to connect any further wiring besides mounting the transformers, but the PT buzzes noticably and the OT still has hum.

The Hammond chassis is 12 x 10 x 2 and the transformers must be mounted horizontally because the chassis runs vertically.  If the transformers were isolated with grommets, I'm afraid they won't hold securely.

Suggestions?

Thanks,
CHAD

I would suggest seeing if the screws on the end bells are tight. I would also try tapping the steel of the transformers a little to change the residence of the unit. Also check the grounding of the circuit. If it is not grounded right, it can cause hum in the output transformer.

Brian Weston wrote:

OK.  I will report back.

Thanks,
CHAD

With the iron mounted and the amp wired up, the buzz is gone.  Sounds like I jumped the gun and panicked before it was necessary.  Thanks Edcor.

CHAD

Glad to hear it, or not hear it. :-)

Brian Weston wrote:

I use a XPWR137-120 transformer to power a stereo P-P EL34 amplifier. Is is bolted directly to a steel chassis. When the amp was fired up I heard a faint hum coming from the transformer bells... (not sure if it was 60Hz or 120Hz). The noise was stopped by placing a couple of small (1/2" diameter) super-magnets on each bell. By sliding the magnets around the bell I could find locations where the mechanical resonance was killed and silence returned.