Yaesu FL-2100B HF Amplifier
When I received this 600W HF amplifier it would pop the tubes as soon as transmit was attempted. After some research I discovered that this was due to an instability which made it susceptible to VHF parasitic issues. I now have Rich Measure's VHF parasitic suppression kit installed and replaced the electrolytic capacitors.
It is a solid performer and a good addition to the shack.
Although I am not very interested in QRO, this is a keeper and is ready to use with my FT-101E station. Now that the solar cycle is headed down this amp will be very useful at times.
The AmpKey interface is essential, giving isolation between the TS-590S and my old Yaesu FL-2100B 600W HF Amplifier.
Amp tubes. Not a matched set but they work well together and I can develop the full 600W although I seldom use the amp.