HP 741B AC-DC Differential Voltmeter/DC Standard Teardown & Restore - Page 1
Forum section: electronics / testgear

author: gilbenl
author_rank: Regular Contributor
timestamp: July 03, 2015, 07:42:55 pm
content: 99% of you won't care about this thread. For the other 1%, lock the door and turn down the lights...I'm fixin to throw up some1967 precision porn in here. This is just a set of quick snaps I took before I closed it back up and turned it on. The good news is the oven is fully functional and correct. Bad news is I get no output on the 10, 100 and 1kV ranges. Since the reference works and is stable, there's really nothing that can't be fixed and that process will follow in the coming weeks. Worse come to worst, I at least have a backup oven for the 735A.Brief history (or at least what I know of it or think I know)-The 741B is the cousin of the 740A/B, extending capabilities to include differential AC voltmeter. They both use the same ovenized voltage ref, which is also found in the HP735A DC Transfer Standard. A gain amplifier provides up to 1000V output. The AC input is provided via a permanently attached tweezer style probe. I believe this and/or the 740B was HPs final foray into voltage calibrators.For now, sit back, relax and drool over something you probably won't ever see in real life.Dirty talk...OverviewGod, please let those caps be good...Reference OvenModulator/Demodulator...anyone spot the problem with it?Range SwitchingPictures of individual boards and the precision divider to follow with the restoration/repair process.

author: free_electron
author_rank: Super Contributor
timestamp: July 03, 2015, 08:00:44 pm
content: loose wire on demod.even though i would never buy such 'old' equipment i can appreciate the build quality. not s peck of dust in sight, everything neatly in cans. bolted down. wires neatly in harnesses.and not a 'glass balloon with scraps of metal in it' in sight.

author: gilbenl
author_rank: Regular Contributor
timestamp: July 03, 2015, 10:09:01 pm
content: Quote from: free_electron on July 03, 2015, 08:00:44 pmThat's exactly why I buy this kind of stuff and get the pictures on the web. All the better when someone who's not a vintage volt nut appreciates some hand looming.Of course I have my "working" stack--modern DMMs, function gen, PS, etc. I consider the purchasing of these old beasts to be a donation in respect of a group of smart guys with flat top haircuts, skinny ties, and horn rim glasses who put a lot of engineering into what HP used to be. They do have their practical applications-This in particular is sufficient to calibrate DMMs up to 5.5 digits. Sure I could do the same thing with something the size of a deck of cards but oh, the smell...

author: Vgkid
author_rank: Super Contributor
timestamp: July 03, 2015, 10:43:25 pm
content: Thanks for the pictures. I take it you must live in Minnesota,or close to it.

author: free_electron
author_rank: Super Contributor
timestamp: July 03, 2015, 11:42:30 pm
content: Quote from: gilbenl on July 03, 2015, 10:09:01 pmit's cool to look at them , in a museum. buying them ? not for me. these machines may look cool and are very high quality but they are impractical to use.

author: PTR_1275
author_rank: Frequent Contributor
timestamp: July 04, 2015, 12:20:36 am
content: Wow, that is very clean inside. Hopefully there hasn't been too much damage from that loose wire.My gear has just left America so hopefully I will have some photos in a week or so.

author: eas
author_rank: Frequent Contributor
timestamp: July 04, 2015, 03:53:32 am
content: Thanks for posting!

author: retrolefty
author_rank: Super Contributor
timestamp: July 04, 2015, 11:13:03 am
content: Thanks for the teaseThese are the kind of threads that brought and keeps me hanging around here.

author: Rupunzell
author_rank: Frequent Contributor
timestamp: July 04, 2015, 02:35:48 pm
content: Very nice.This is the kind of test gear Bill & Dave's hp once built that resulted in the legendary hp reputation for quality, reliability and much more.After this 714B has been restored to proper working condition it will likely out last it's current modern replacement long after the modern plastic-surface mount wonders have been shoveled into the dumpster with no service or parts support . Most everything is serviceable in hp test gear from that era.Worth noting that Fluke also built Diff volt meters and Voltage standards like this. It is likely hp designed and offered the 714B in response to the Fluke series of Diff volt meters and Voltage references. At the time Fluke had a large share of that market.Berncie

author: Anthony60
author_rank: Newbie
timestamp: May 03, 2018, 10:51:09 am
content: Hi,Wondered if you have got any closer to sharing the teardown and restore of the HB 741B ?I'd be very interested in what problems you have had restoring the unit ?RegardsAnthony