[Johnson] Valiant Modulator Help !!!

[w0ng at adelphia.net]

It appears (?) that the original modulation transformer in my 1957 Johnson Valiant is toasted. At least when I see whisps of smoke coming out from under it, I assume it is. Gee... it only lasted 49 years!  

It's been doing fine until this afternoon when the xfmr started "singing-it's-head off" with modulation applied from my Heil Classic mic. The modulated waveform now looks TERRIBLE!  Doesn't even look like a modulated AM signal anymore. 

Very distorted waveform...hard to describe but flat-tops with just a little modulation. Using an audio oscillator with 1KHz sine wave output instead of a mic, the waveform has sharp multiple peaks instead of rounded ones (??). With the audio oscillator at its lowest output, couldn't get to 100% modulation, positive or negative. Started sounding like the mod xfmr was going to vibrate apart.

Before this, it was fine. AM waveform now LOOKS TERRIBLE on the scope. Carrier waveform is fine.

It was out of the cabinet and on the workbench at the time I saw smoke (when modulated) from under the xfmr. I also saw a brilliant "arcing" on the terminal strip under the chassis where the plate leads (new HV wire) from the modulator tubes are connected to the xfmr leads. It was arcing between the two plate lead terminals when modulation was applied.

Changed out the 6146's with a pair of known good tubes and the arcing stopped (?). 

Idle mod current is good. I used to have a smooth rise in mod current as the audio pot is advanced while talking, but now it's acting erratically. I haven't yet unhooked the wires to the xfmr to do an ohmmeter reading. I thought I'd ask the group for some advice before I heat up the soldering iron. 

Maybe I'm missing something else in the modulator circuit that's going haywire??? Any advice would be greatly appreciated.

If it is the mod xfmr, I'd appreciate some suggestions for a replacement. I know Peter Dahl ($$$) sells them and Gary Brown, WZ1M can re-wind mine but was curious if I'm overlooking other possible sources.

Thanks in advance,
Bill
w0ng