[Amps] 2x8877 question

[Stan C.]

Hello gang.
 I have a amp running two (2) 3CX1500A7 tubes. It was built to use on 75m AM. Here is the problem. With it keyed....no modulation....the grid current is about 40-50 mills. When speaking though the grid current peaks to 200+ on voice peaks. Using the "load" to bring it down really brings down the output. I have ran other amps (Alpha 89,Command 2500E,etc) and have had no problem keeping the grid peaks down by advancing the load. But only loosing 100-200 watts output. The transmitter is a Johnson Valiant. 
 I am wondering if I increase the bias voltage from the current 8.2 to say 12 or 16 volts if this will help out. I know I will have to drive it a bit harder to get a given output with the higher bias voltage,but that is no big deal.
 Any help from the knowledgeable would be greatly appreciated.
 
PS....plate voltage is 3900v under load.
 
Take care,Stan