Based on the G12T-75 12" guitar speaker, the beefier G12T-85 Rivera gives you classic British tone with a warm body and distinctive growl. It takes the sound of their original G12M Greenback ceramic speaker to the extreme. Characterized by its massive bottom end, laid-back mids, colorful highs, and extreme volume handling."  The G12T-85 is exactly as the G12T-75, but with a larger (50oz)ceramic magnet, and a more focused field to give tight control, punch and definition. The "T" series was used more in the JCM 800.