[AMRadio] Modulator testing

[Jim Candela]

 Bob,
   I would not do that. It was wise to hesitate. It is usually unknown how much voltage can be applied between the primary and secondary windings. I once wanted to do the same thing with a quad of 808's in push pull parallel. Fair Radio used to see the 808's for 75 cents apiece. What I did was to hook up the HV windings to a big plate transformer, and then load the AC line side with a resistance that took into account the turns ratio of the plate transformer (impedance varies as the square of the turns ratio).
This is not ideal, but no faults occurred.
Don't even think about floating the scope!! NO!!

JimWd5JKO

    On Monday, January 14, 2019, 8:02:14 PM CST, Robert Nickels <ranickel at comcast.net> wrote:  
 
 I'm testing a modulator running a pair of 811s, using a resistive load 
in place the final amplifier.    Normally both primary and secondary of 
the mod transformer have HV applied, so they are at the roughly the same 
DC potential above ground.  To make accurate measurements using a 
grounded oscilloscope,  I am wondering if it would be save to ground one 
side of the secondary where my resistive load is attached.    Both 
windings are obviously rated to withstand high voltages  with respect to 
the frame,  but I can't find any manufacturer's name or part number on 
it, and while I assume the isolation between windings would be 
sufficient,  I'd hate to cause a problem.

Thanks and 73,
Bob W9RAN

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