The 4CX350A/8321 has a maximum plate dissipation of 350 watts and is intended for Class AB audio or RF amplifier service. The tube is externally identical to the 4CX250B but contains rugged internal construction features. Amplification factor and cathode area have been increased over the basic 4CX250B to give higher transconductance and figure of merit.

The 4CX350AC/8321A is a compact air cooled tetrode. This product is intended for use in equipment which normally uses the 4CX350A, and where extended tube life is a concern. Externally, the 4CX350AC/8321A is identical to the 4CX350A. Electrical characteristics are the same in both tube types with the exception that the heater warmup time is increased to 40 seconds in the 4CX350AC/8321A.

The 4CX350F/8322 has a maximum plate dissipation of 350 watts and is intended for Class AB audio or RF amplifier service. The tube is externally identical to the 4CX250B but contains rugged internal construction features. Amplification factor and cathode area have been increased over the basic 4CX250B to give higher transconductance and figure of merit.

The 4CX350FJ/8904 is intended for Class AB linear RF amplifier service. The tube has rugged internal construction features. The 4CX350FJ/8904 may be used as an exact replacement for the 4CX350F/8322 in most linear applications, requiring only minor circuit adjustment and retuning. The tube has improved intermodulation distortion characteristics. It contains a 26.5 volt heater, and is recommended for new equipment designs.