Looking at the 1N831 data sheet, it appears that this is a fairly generic Silicon RF diode, and in fact looks like originally spec'ed as a mixer diode.. I am fairly sure that any HP leaded Schottky diode would work well here, like a 5082-2800 or 2817 type. Maybe even a BAT-85, which I have used on a crappy FR-4 board to over 1 GHz with pretty good flatness. The magic is the coaxial diode mount with the disk resistor & capacitor to give low parasitics in a ~50 ohm coaxial line circuit.
Jeff Kruth
In a message dated 2/9/2022 1:08:43 PM Eastern Standard Time, davewrightsplace@... writes:
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The HP 8471A OEM diode is 1N831, and there are some on eBay. I have two on the way now.
Left to right in the photo is the input termination resistor, 50 Ohms, some sort of film deposited on the disk between the BNC male center pin and a contact ring to the case. The diode anode lead is soldered directly into the input center pin at 'zero length'. ?The cathode lead passes through the center of a disk capacitor, measured as ~1500pf, and on to the center pin of the output BNC female.?
The assembly process will require care in soldering, I imagine it will go as: input R first, then output C, then screw gold plated center into the BNC male body, solder BNC female center pin to protruding cathode lead, and thread main body over all.
Intend to measure performance on 8753D VNA when completed.
