[Amps] Problem with amp conversion-help requested

[John]

Gentlemen,

I've completed the GI7B conversion of a Dentron GLA1000.  I've added the 
tuned input board, rewound the output tank coil, built the cooling 
enclosure, redone the bias , etc. On 40 and 80, all is well, and the amp 
works as I'd expect. On 20m, it also works well, but when I advance the 
drive beyond about 25 watts, the amp takes off (plate current rises, output 
power rises) and if I don't get the exciter off quickly , there's an arc in 
the tune capacitor.  The conversion was modeled after that of N8GPQ.

I've rewound the  "parasitic choke" (47ohm 2watt resistor  w/5 turns), with 
no effect, and wonder where to go next. I've really learned a lot with this 
conversion, and it looks like I'll learn some more as I try and track this 
phenomenon down.

Where would you go first, if trying to chase down this issue?  Since I 
built the thing from a bare chassis, I'm not afraid of digging in.

Thanks for any pointers
John K5MO