General Radio (Genrad) Model 1666 Precision DC Ohm Meter 

I entered college in 1967 and around 1969 we had a four function "digital" calculator in our physics lab we were supposed to marvel at. At the same time, the most sophisticated calculator we had was a slide rule and there was a full semester course on it. The part that I wanted to run from was the pencil and paper arithmetic division and subtraction. It was terrifying... lol... on the other hand, I loved the calculations and the higher math so it is interesting where we want to draw the line in our love of technology. Calculating everything 1940's style makes me admire the guys that preserved thru it but now it is all an app on a PC. I get it when it comes to solving problems and progressing thru a design or solution to a problem but in the personal sense, I still appreciate and like to engage in that stage where analog calculations are satisfying. Of course, I cheat and use a HP RPN calculator and would run from the pencil-and-paper method of arithmetic as already mentioned. Also, there was a spirit even into the 1970's where we wanted to build the very best - something that could be repaired and last forever. Every nut and bolt in the big mainframe computers were real USA stainless steel. We could not conceive of the throw-away society we live in today. I don't want this to sound unappreciative or bitter in any way. If I was working today I would want the best digital instrument to get the job done right. I spent 26 years with NASA and WSMR in the computer world and the Lockheed guys took care of the huge UPS systems and would talk about having to measure those micro ohm resistances you mention in the battery banks that supported the range control center. Even a milliohm at 4000 amps is a 4 volt drop and that might not be able to be tolerated. The last computer I worked with was a water cooled unit that had a logic voltage of 2 VDC with currents as high as you mention. Multiple parallel lines of large copper straps between the power supplies and the logic rack. I have a new megger and it is amazing accurate for very little money but this old GR stuff has a different soul. Thanks for your comments. Stay safe.

For the extreme limits of resolution of, 1 u ohm and 1 T ohm, I agree that they should have used a mirrored scale to minimize parallax. I realized tonight just before this video that I was having some slight issues with stability and accuracy so I measured each D cell under load and found that four, in one group, were equally weaker than the other group of four. Apparently, one group of four is under a heaver load than the other bank. I swapped two between the groups of four and balanced the set and it settled right in. These old instruments take TLC to make them purr.

Hi Bill, I have been alone now for just over a year. It is still very tough but somehow I seem to be able to keep going... my outdoor feral momma cat gave me four beautiful kittens that I enjoy along with my Angel cat that is my indoor cat. My momma cat is not eating well and seems thin and I am worried that she is sick but I can not touch her and wish I did not have to traumatize her further to catch her and take her to the vet but I should do it tomorrow. I have wonderful friends here in El Paso that I stay in contact with and I am slowly getting back into my hobbies and enjoying them. Thank you for thinking of me and keeping in touch. I hope you are doing well and enjoying your hobbies and life is gentle with you. 🙂

I use the sensitivity control also. The Zero and Sensitivity work together and the instrument needs to "warm up" and settle down for a good 30 minutes before the sensitivity can be advanced to maximum and maintain a Zero. I wish I had shown how easy it is to measure and see the difference between a copper strip vs a silver strip. I have a silver strip made from the .999 silver cubes of 1 troy ounce that I have used to silver plate so it is thin and about 10 inches long and an inch wide. I have couple of of the silver cubes left, about the size of a sugar cube, and can see that clipping the Kelvin probes across the cube shows zero resistance as would be expected. It confirms to me that instrument Zero and "zero" resistance is the same meaning that the cube has a resistance using the Kelvin probe well below 1 u ohm which is the resolution of the instrument, As you discovered, a unit that is "not operational" could possibly be OK and maybe the previous owner didn't know how to use it. Your understanding saved the unit from the trash bin or being parted out and sold on Ebay. I agree that the GR standards - resistors, capacitors and inductors bring a high price. I have a few resistors, capacitors and inductors I use for calibration checks. Possibly more money to be made on Ebay parting a unit out rather than selling a whole unit. The Z-Y bridge I have requires a signal source and a detector so it could easily be seen as defective, or just too much to buy the other instruments to those not familiar with this type of equipment. Thanks for your comments. It is always nice to see others that appreciate this magnificent equipment. Stay safe.

Thank you. For all practical purposes, the 807 is a 6L6GC with the plate connection on top so the plate voltage can be as high as 750 VDC. I didn't know anyone made that type of adapter. I just looked them up on Ebay - sounds like fun to me. 🙂

Thank you. I am pleased you enjoy the vintage equipment. I often times, when I get a new piece of digital equipment, check its accuracy with my analog GR instruments. With that said, I am generally pleased with the precision and calibration of much of the affordable equipment available today. Thanks for your comments.

@@ElPasoTubeAmps Hi, do you see an Output Transformer with 500 Khoms in the primary? Genrad make a very good quality test equipment. Best Regards. I