Attached below is a greatly improved 3-diode negative peak limiter with results as to why it is improved. After much experimentation with my transmitter I discovered that the current flowing through diode D3 in the circuit hits a brick wall as the circuit AC conducts. This was observed as random transient voltage spikes on the modulation envelope during modulation. This was further verified by running additional tests with a spice simulator and it shows exactly what happens during 150% modulation peaks. Without the addition of R2 in the circuit there is no way to prevent the spikes from occurring. The values of both R1 and R2 must also be 2 times the RFPA plate load ohms because they are essentially in parallel with each other during the negative half of the cycle. This is also more than likely why other hams through the years have reported the diodes often being blown and it's probably because of the transient spikes. It's also likely to cause excess splatter on the bands when it happens as well. .