I've always used cheap Calrads on mine. They only work in stereo mode. If you switch to mono they won't work! Go figure?

Free repair and replacement of the whole unit or defective parts is only good for the first year. The second paragraph of my waranty card reads:

"During the second to fifth year, FRL will replace defective parts at no charge except for repair and return postage". From the second year on, you're gonna get charged labor. Considering the cost of labor these days, I think that I'll convert my CZ-7A to a door stop or boat anchor should my unit fail again after 2-5-2000.

As a side note, the housing is glued together with KTV cement or sealant. When I got mine back when I made the direct trip to Los Banos, the unit was returned held together by rubber bands. They said to wait 12 hours before using it. I've used lots of different cements and sealants but never KTV. Unless one knew what solvents to use, I'd be real carefull dissassembling the housing.