I worked at HP in the 1980s, and I repaired many of this specific model number. The reason HP designed this hybrid was for 2 specific reasons: First, because the voltage divider resistors could be more easily laser trimmed for precision. Secondly, and more importantly, the switching FETs were added onto the same substrate as the resistors for temperature stability. The theory was that any thermal drift would be minimized due to the added mass of the substrate, and in any case, all components on the substrate would drift equally in the same direction, thus effectively canceling the net effect of temperature changes. The idea worked reasonably well, and it is still used today in modern instruments. Your idea of building a replacement board for that hybrid is excellent, but of course the thermal benefits of that hybrid will be lost. In practical terms, I would think it would work fine, considering the level of precision expected from this instrument.
I am really enjoying this series of videos and look forward to the next part. Caddock make precision voltage divider resistor networks with the ratios that you need - if you would like to avoid trying to hand select a matched set. Regards, David
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I worked at HP in the 1980s, and I repaired many of this specific model number. The reason HP designed this hybrid was for 2 specific reasons: First, because the voltage divider resistors could be more easily laser trimmed for precision. Secondly, and more importantly, the switching FETs were added onto the same substrate as the resistors for temperature stability. The theory was that any thermal drift would be minimized due to the added mass of the substrate, and in any case, all components on the substrate would drift equally in the same direction, thus effectively canceling the net effect of temperature changes. The idea worked reasonably well, and it is still used today in modern instruments. Your idea of building a replacement board for that hybrid is excellent, but of course the thermal benefits of that hybrid will be lost. In practical terms, I would think it would work fine, considering the level of precision expected from this instrument.
I am really enjoying this series of videos and look forward to the next part. Caddock make precision voltage divider resistor networks with the ratios that you need - if you would like to avoid trying to hand select a matched set. Regards, David
But the matching (with a KVD) will make for a fun video ;-)