[Amps] 60 Hz B+ Ripple

[Wayne, W0ZW]

I recently had reason to look at the purity of the B+ supply voltage for my Ten-Tec Titan amplifier.  Not having HV measurement equipment, I hooked a scope probe to the end of the voltage divider circuit which feeds the metering circuit.  The voltage measured by the scope was 4.8 V (representing the normal 2,200 V B+).  

The disturbing thing I noticed however was a ripple voltage at 60 Hz (not 120 Hz as I would expect).  This is from the output of a full-wave bridge rectifier circuit with 8 X 400 uF of filtering.  If I do the math the actual ripple voltage works out to about 32 Vrms or 1.5%.  I believe this is an acceptable level of filtering .  

Why is the ripple voltage a 60 Hz signal?  I disassembled the PS unit and each diode in the bridge circuit tested good, so I believe I am indeed getting full-wave rectification.

Is the 60 Hz ripple I am seeing a result of transformer external inductance?  In other words, induced voltage from the 45 lb. Hypersil transformer on the wiring in the power supply box?  As a point of reference, I do not see a 60 Hz ripple on the +28 V voltage for the logic and control circuits.  It is provided by a separate secondary winding on the same transformer.  

Perhaps this ripple has been present since I owned the amp and I just didn't know it.  Short of magnetic shielding can anything be done about it?  What am I missing?

Comments/feedback welcomed.