This op uses a 51S-1 for SSB communication, paired up with a 32S-1 and a 30S-1. Wouldn't think of changing it. It's the "28 volt" (25.2V is where I run it) model and I've placed a small muffin fan under the lid to exhaust air. Anyone interested in an operational HQ-215 in trade for their operational 51S-1? Rolynn