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The excessive heat and inability to sustain the carrier are key signs of thermal runaway. You are right at the brink of a transistor failure and a long transmission could do it. The idea of replacing the CB finals with Mosfets is good if the bipolars are obsolete but not the best idea if you want 80 watts. Nothing in your CB was designed to cope with the currents involved here from the power cord to the modulator stage.

Do you have any idea what happens to the impedance the modulator sees when the final stage current increases to make 80 watts? It drops several times lower then the stock impedance and causes premature flat topping with bleedover. It's much easier to add a stage of linear amplification then it is to properly get more watts from a stage that has to be high level modulated.

[QUOTE="Shockwave, post: 232240, member: 10882"] The excessive heat and inability to sustain the carrier are key signs of thermal runaway. You are right at the brink of a transistor failure and a long transmission could do it. The idea of replacing the CB finals with Mosfets is good if the bipolars are obsolete but not the best idea if you want 80 watts. Nothing in your CB was designed to cope with the currents involved here from the power cord to the modulator stage. Do you have any idea what happens to the impedance the modulator sees when the final stage current increases to make 80 watts? It drops several times lower then the stock impedance and causes premature flat topping with bleedover. It's much easier to add a stage of linear amplification then it is to properly get more watts from a stage that has to be high level modulated. [/QUOTE]

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