Cushman was a popular test equipment manufacturer based, I believe in San Jose, California. They made all manner of RF test equipment from service monitors and, spectrum analyzers to microwave test equipment like selective level meters and signal generators. Nothing they made was especially terrific in any way, but it was certainly usable by the target customer base: the two-way radio industry. Their hey-day was in the late seventies and early eighties, but technology moved faster than they could adapt, and now they are history...

I have a half dozen Cushman monitors I picked up from salvage in rough condition. They were used by a large company to service radios in the field and at the bench, so they all show signs of travel. None of them worked as delivered, but they all look serviceable. I chose to do the CE-5 first, because it appeared to require the least amount of effort to get going -- I needed an easy success at the time!

My first Cushman was a CE-6, way back in early the eighties, very similar to this one, but wider frequency range. This was another reason to start with the CE-5: familiarity. The CE-5 has a directly tunable range of 20-519 MHz, and by using IF frequencies and harmonics, can be made to work from 0-1000 MHz. It generates signals up to -47 dBm, with AM or FM modulation, and demodulates FM with deviation measurement and frequency error measurements. The time base in this thirty year old machine is tremendously stable, exceeding my ability to (easily) characterize even with my 1 PPB frequency standard. This will make a great HAM radio test set!

I started, as I usually do, by tearing the machine down and cleaning everything. Each of the dozen plus modules were removed, cleaned, and repaired as needed. Next, the chassis was scrubbed clean along with all the switches and pots. This was done in steps: I actually used Windex and a toothbrush to clean most everything, followed by rinsing with clean Windex, and then blowing all the moisture away with compressed air. The Windex was an experiment chosen because of its fair cleaning power and low residue, it worked fairly well too. Next, I used a plastics-safe (Tested!) contact cleaner to remove any Windex residue. The type I used was highly flammable, so precautions were observed. The excess contact cleaner was blown away with compressed air. Finally, contact restorer was used on all contacts, pots, and switches. Some of the boards had thirty-year old solder flux on them, this was removed with flux remover before the cleaning. Surprisingly, I found no loose screws, anywhere! What I did find was that Lock-Tight or something similar, had been used throughout -- Go Cushman!

Once all this was completed, I pulled all the incandescent bulbs out and tossed them. They were all replaced by 7000mcd LED's. These were wired in with a rectifier diode and a current limiting resistor. The rectifier was needed due to the fact that the bulbs had been fed with AC. This worked great! No more bulbs to replace, ever again.

The scope tube was on the dim side, usable but noticeably stricken with cathode poisoning. I ran it through a twenty-one hour rejuvenation process I found in a Hewlett-Packard memo. This was the first time I had ever tried it, and it made a big difference. Most notably, the brightness control acted linear again! Before, it was dark until almost at full brightness, and would then brighten up all at once. Now it brightens up gradually. It is no brighter than it was before, but now it works like it should. HP recommended that the rejuve be done twice, but I stopped while I was ahead -- just once. 

In a nutshell, here is the process:

Isolate the filament from the original power supply and connect to an AC transformer through a Variac. Then follow the Voltages and durations in the chart. (I used a 12.6 Volt transformer through my Variac -- This allows a variable output of 0-12.6 Volts AC. Some people use DC for this because it is easier to come by, but filaments were designed to operate from AC, not DC, and many experts suggest that DC will be less effective at best, and damaging at worst.) Note that the last five steps are performed with the anode and cathode at operating voltages. Be sure to check the maximum potential difference allowed between the cathode and the filament!! You may need to have a resistor in place to raise the potential at the filament, which will be dangerous! Use brains and caution! Be aware that your isolation transformer must be able to withstand the isolation Voltage as well!

Calibration information on the CE-5 is unavailable. I did find a copy of the manual online, a terrible copy with limited service information. The calibration in the manual was limited to trimming, rather than full, detailed instructions. This was enough to get the monitor in usable condition, but I am not willing to risk throwing it out of working condition to experiment on calibration. Monitor functions work well, deviation measurements are reasonably close, and output levels are very usable, though off by as much as +10 dBm. Deviation was checked using the Bessel function -- a very simple and accurate method. The frequency accuracy is better than 0.0036% and short term stability after warm up is better than I can measure -- Most excellent.