[AMRadio] Modulator testing

[Robert Nickels]

To close the loop on this issue, it turned out that the very thing I was 
hoping to avoid led me to discover the problem.   I decided to ground 
one side of the mod transformer secondary which was disconnected from 
the RF deck and only connected to my resistive load in order to get 
accurately characterize the modulator.   But the 10A plate HV fuse blew 
instantly!   An ohmmeter check confirmed the obvious conclusion  - the 
transformer has a 120 ohm short between primary and secondary.    I'd 
measured the individual windings many times but hadn't thought to check 
between windings.   I even thought about hi- potting the thing, but 
since there was no arcing or breakdown I didn't, although I probably 
would have caught it if I had.

The transmitter in question is an Eldico TR1-TV, which is pretty 
uncommon and the only other one I know of has had its mod transformer 
replaced too.  I put in a mod transformer from an ART-13 which is 
working  much better - with 100% negative peaks and 50-60% positive 
peaks.    When I got the transmitter the original plate tank coil was 
missing,  so I've been trying to figure out the correct inductance and 
tap points,  - a process that was complicated by (and contributing to) 
the low modulation problem.    So I still have some optimization work to 
do but it's always good to find a definite problem, even if it's in an 
unobtainium part like this mod transformer.

And then while testing the Millen HV connector zorched itself. No doubt 
the worst product the James Millen name appeared on.

73, Bob W9RAN