[Test-Equipment] Crystal Marker Boards for HP 675A Sweeping Signal Generator

[Dale H. Cook]

At 12:05 AM 5/22/2014, Pete Lancashire wrote:

>I don't have a manual for the markes but would be willing to help.

Help, in the sense of physical technical help, is not what I need - I have been collecting and restoring HP and other laboratory grade instruments for nearly forty years.

The crystal markers other than the 100 kHz and 1 MHz markers must have sold poorly - every 675A photo that I can recall seeing had the same three labeled buttons as mine - the marker rotator and the 100 kHz and 1 MHz comb filter markers, and had no labels on the D through H buttons for the optional crystal markers (HP supplied button labels with the crystal markers). If I can't scare up a manual for the 11300A I can try rolling my own boards. The boards for the 100 kHz and 1 MHz markers are shown in the manual, are identical except for crystal, and the optional crystal markers, at least for the lowest frequencies, would certainly have used the same circuit and board layout. I popped the hood on the 675A this morning to have a look at the 100 kHz and 1 MHz marker boards and, as I expected, the 100 kHz crystal is in an HC-13/U holder and the 1 MHz crystal is in an HC-6/U holder. Both, of course, are fundamental-mode crystals. It is possible that at some higher frequency the design shifted to an overtone-mode crystal.

I have a number of crystals in both holders. I will run the HC-6/U crystals through my crystal checker to identify the fundamental mode crystals. I can the pull the 1 MHz board from the C slot, change crystals, and put it into the D slot to try to empirically establish an upper frequency for that board. I may end up deciding this project is more work that it is worth, and just pick up a good used synthesized oscillator for an outboard marker generator.

Dale H. Cook, GR / HP Collector, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcity/radios/index.html