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2026-10-18 19:26:42RF Boneyard AdminFeatured

Marconi 2955 OM345 RF Amplifier Failure

# Marconi 2955 OM345 RF Amplifier Failure — Rebuilding the Obsolete Hybrid Module I'm starting a new restoration and reverse-engineering project here at RF Boneyard involving the **OM345 RF hybrid amplifier module**, a component known to cause trouble in vintage Marconi communications test equipment, including the 2955 series. Anyone who maintains or restores these instruments knows that keeping them operational is becoming increasingly challenging as certain original components become difficult to obtain. The OM345 is one of those components. There have been various approaches to repairing failed OM345 modules, including modifications to the original hybrid and attempts to construct modern replacement circuits. **Our goal at RF Boneyard is to investigate reproducing a functional replacement for the original OM345 module.** I have already acquired a board for this project, and we're planning to examine the circuit, investigate its design, and work toward building and testing a replacement. Ideally, we'd like to create a replacement that can help keep these excellent instruments operational for many more years. ### Has anyone successfully built an OM345 replacement? I'd particularly like to hear from anyone who has: - Built or tested an OM345 replacement PCB. - Reverse-engineered the original OM345 hybrid circuit. - Experimented with substitute RF amplifier components. - Measured the gain, frequency response, or impedance of an original or replacement module. - Repaired a Marconi 2955 or related instrument suffering from an OM345 failure. If you've already built a replacement, I'd be especially interested in learning what worked, what didn't, and whether the replacement performed reliably in actual equipment. ### An ongoing RF Boneyard restoration project This is an early-stage research project, and I'll be sharing our findings, photographs, measurements, and progress here as the work develops. The objective isn't simply to replace a failed component. It's also to preserve the technical knowledge needed to maintain these classic communications test sets. If enough information can be gathered, perhaps we can eventually develop a practical and reproducible replacement. **Have you encountered a failed OM345? Have you repaired one or built your own replacement?** I'd welcome hearing about your experience. — Joe
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