[volt-nuts] HP 741B AC-DC Differential Voltmeter/DC Standard

[gilbenl at nickgilbert.org]

All-

Recently picked up an HP 741B, a cousin of the 740B. Wondered if anyone had ever heard of/used/owned this particular model? Strikes me as somewhat of an odd beast in that it shares the same reference oven, production period and ostensibly similar niche as the 740, with the notable addition of AC measurements, yet it has slightly lesser performance (Stability is 3ppm/hr setting, 1ppm/hr range vs 1ppm/hr setting, 0.5ppm/hr range). Curious as to who the target market was? Seems like the 740B would be the choice for DC and another mfr for AC, particularly since it doesn't offer a built in standard.

Beautiful cosmetic condition inside and out. No signs of someone messing around with the internals in a past life. Reference oven is good and provides output on the 1V range, but unfortunately the 10, 100, 1kV outputs are nil. Visual inspection didn't offer any overt failures, but given the issue is on all ranges except that which is coming straight out of the ref, the issue likely resides between the diff amp/power switch assy and output. For those in the know, everything probed as expected except the collectors of A7Q1 and A7Q2, which were flat.

Anyone have any pearls to share that may save me some time?

-Nick