[Milsurplus] The FR-38 Saga, and GF-11 diodes

[Ray Fantini]

Ended up using just some generic 1N914 diodes that I had laying around the shop. Had only two original diodes that were way under the minimum reverse resistance per the manual specification of 75K Most of the Germanium diodes if not all have some leakage and would be good to replace most of them at some point in the future but the replacement of the two leaky ones got my gate trigger MMV up and running. The next problem was the decade divider that divides the signal from the time base was only dividing by two. That's mounted on a sub assembly and is removable so after removing, checking the tubes and cleaning it up somehow it magically started working again. Suspect that there may be a bad 0.01 cathode bypass that's causing it to run as a MMV and not a flip flop and may go ahead and change that while it is out.
With the gate circuts now all working and after completing a time base calibration late last night I was able to do a successful self-test of the 100KC and 10 MC internal reference oscillators. All of this was with the input section removed but have seen it generate output so going to assume that there are no issues with that. The next step will be putting everything back together and all the covers on and seeing if it still works then.
Working on vacuum tube digital electronics has been a learning experience and armed with a good dual trace scope and service manual not as daunting a task as I assumed it would be when starting but have to say that without proper documentation and the excellent service manual that not only included schematics, waveforms and most important theory of operations would not have been able to do it. Also thanks to everyone who helped out with the diode question. Think what I will do on that front is maybe next year at Dayton will stop of at Midwest Electronic Surplus and see what they have in a bunch of identical small signal switching diodes and try the dreaded shotgun approach to try to keep all the diodes the same type.

Ray F/KA3EKH
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