Legal Limit The Easy Way

This simple to build, inexpensive amp is capable of running 1500 watts out without stopping to take a breath. And, although designed around a tube that may be purchased quite cheaply on the used market, it's flexible enough to accomidate a number of other power triodes and tetrodes as well. I have successfully built two versions of this amp, and presently use it on a regular basis. What makes it work is the simplicity of design. Placing the grids directly to ground and keeping the input circuit as simple as possible is key to its success. Additionally, the design does not employ an ALC circuit, which, in my opinion, is most often a source of needless grief. A superior resource that I use on a regular basis - my ham bible, or sorts - is listed at *Reference Materials. It provides, in simple, understandable terms, every detail any ham may need to both design and build a vast variety of equipment.

The circuit outlined here was originally designed around a pair of tetrodes that were utilized by Collins in their "big gun", thoughout the 50s'. Initial tests proved astounding, near 1500 watts out, key down, with less than 60 watts of drive. Tuning, however, was critical and any mismatch required a dramatic reduction in power. To alleviate this problem, heavier tubes were selected. When these were combined with small design modifications, not only did the amplifier perform as well as the original configuration, but became far easier to tune and readily tolerated a moderate mismatch.

The power supply for this amplifier must be capable of delivering 2800 volts DC, at 2 amps, key down. Due to the potential size and heft of the transformer and associated filter components, it is recommended that no attempt be made to incorporate it with the amplifier in a single chassis. Instead, the power supply should be built in a separate chassis, and placed on four quality casters. The amplifier chassis may then either be placed on top of the power supply, or in the operating console, with the supply stowed underneath.