Sulzer Frequency Standards
Sulzer 2.5 Performance Data
In the early 1960s, Sulzer Laboratories produced one of the finest quartz frequency standards ever offered commercially. Even 50 years later, these standards can turn in superlative results.
Somehow, I've collected seven of these oscillators, six of which still work. I recently compared them against an FTS-1050A quartz standard that's known to have extremely good performance from 1 out to several thousand seconds. The plot below shows each of the Sulzers measured against the FTS-1050A. This data is from a 12 hour measurement, after each Sulzer had been running for about one week. The FTS-1050A had been running for about three months.