Hi,

I have used and repaired several of these converters. When they were new, performance was often poor due to the combination of low transmitter power at the UHF TV station, and the high noise figure of the diode mixer in the converter. Today, most UHF stations use much higher power levels, so performance of the converter is usually pretty good. If you do encounter very weak, noisy reception even on strong signals, the diode mixer is a likely culprit. Look for a small brown cartidge in a clip in holder, usually located on top of the chassis. The diode can be snapped out of the holder. You can use a 1N82A diode for a replacement, often with a phenomenal improvement in performance. Of course, make sure the tubes are good. Good luck!