I extensively studied the 5061 harmonic generator when I was designing the harmonic generator in the 5071A. We are now going on 30 years since that work. The diode had some HP part number. Even if you knew this part number, you would need to have the Part Information Report microfiche that gave the vendor part number. The chances of this diode still being available are very slim. So you are not going to get an exact replacement, except by cannibalizing another 5061 harmonic generator assembly, assuming it doesn't also have a bad diode. As far as replacing it with a different diode, that too would be questionable. SRD's have magic unspecified parameters when it comes to what they do in a circuit. The 5061 generator in particular has extremely high efficiency due to its unique design. It was designed by a Korean professor named Soon Choi (IIRC) who spent a summer at HP. He left no known documentation as to how the design works, or how to specify the SRD.
After a long period of study, I concluded that I was never going to match the efficiency in any simple circuit. The diode mounted directly in the waveguide is the magic. Fortunately, by that time, we could use a phase locked DRO and get around this problem. Len Cutler in his usual style criticized me for "taking the easy way out", but he eventually came around to my way of thinking. I will give you a little hope. The harmonic generator consists of a bunch of silver plated parts that are supposed to fit together and achieve electrical conductivity. After many years, the silver and tarnish and upset the electrical conductivity. You might try disassembling the diode mount and cleaning up everything. After you reassemble it, you might have good news. I will say that I have never heard of an SRD failing, and as you say, it looks good at DC. What possible failure mechanism could selectively make the diode stop generating harmonics but other wise be OK at DC? Somehow let the pixie dust escape without letting the smoke escape. Seems unlikely. Also check the drive circuitry. SRD's need tricky components to make them "step" correctly. Again, poor grounding due to corrosion could spoil the harmonic generation. Rick Karlquist N6RK Member of the 5071A design team On 12/24/2017 3:54 AM, Kejia Lee wrote:
Dear All, Happy Christmas! May I know if anyone knows the part number or the specification of the step recovery diode in the harmonic generator for the old HP 5601A cesium frequency standard? I recently received this toy. The cesium tube seems to be OK, and I had located the problem being no 9GHz from the waveguide. I checked the diode, the DC properties seems to be OK, but just can not generate frequency comb any more. I really hope I can repair it as a personal new-year gift. I will be really appreciated, if you had any suggestions. Best regards, K. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
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