HP 5265A Digital Voltmeter Plug in photos - Page 1
Forum section: electronics / testgear

author: Cubdriver
author_rank: Unknown
timestamp: July 07, 2016, 02:11:50 am
content: Hi All -I got this little beastie from the 'bay a week or two ago, and finally got a chance to look it over and give it a cursory test. It's an HP 5265A DVM plug in, designed for use with the 5243L and 5245L or M counters. When installed, it turns the counter into a six digit DC Voltmeter with 10, 100 and 1000V full scale ranges. Accuracy is purported to be +/-0.1% of the displayed value if it is greater than 1/10 of the selected range, or 0.01% of the full range if it is less that 1/10 of full range.It is a voltage to time interval converter, so it basically compares the voltage to be measured to an internally generated linear ramp voltage, with the counter counting in the interval between the measurement start and the time when the internal ramp is equal to the voltage being measured, at which point it stops the counter. The resultant count made during the time period that the measurement was taking place is equal to the voltage being measured.It was introduced in the 1965 catalog, and its list price was $575 that year.It was a bit dusty, but other than that appeared to be in good condition so it went into the counter for a test run. It zeroed nicely, but I ran out of adjustment before I was able to get the 8.000 adjustment dialed in - it's still ever so slightly high at 8.0038. It's loaded with old style molded carbon composition resistors, so it's quite possible that one or more of them have drifted out of spec. Something to explore when I dig more deeply into it.Zero (both polarity indicators are lit because at zero they flash alternately and the exposure was long enough to catch both of them lit):8.000 setting:It wasn't too terribly far off reading voltage (mind you this was compared to my old HP 3440A which hasn't had a 'real' calibration yet - I was too lazy to dig out one of my more modern DMMs to compare them to this morning at 2 AM).The 3440A:And finally the power supply providing the voltage:More pics to follow, full gallery at:https://pmanning.smugmug.com/Electronics/HP-5265A-Digital-Voltmeter-Pat

author: Cubdriver
author_rank: Unknown
timestamp: July 07, 2016, 02:43:20 am
content: Its controls are dirt simple, consisting of a range switch, local/remote switch, inputs (a pair of 5 way binding posts are standard; this one also has a BNC jack that was added at some point during its lifetime), zero and 8.000 adjustment pots and a pair of neon indicators to show the polarity of the measured voltage:To operate it, it's installed into the counter's plug in bay, the counter's sensitivity selector is set to the 'Plug In' position and the function switch set to its 'Remote or Time Int' position. Turn the counter power on and you're basically good to go. Zero is checked by shorting the input terminals, and the 8.000 setting checked by putting the plug in's range switch in the 'Cal' position. Each value is adjusted by tweaking the respective potentiometer; the pots are accessible through the front panel.Interestingly, the 8.000 calibration pot at a glance appears to be a standard 3/4 turn unit (it has a very similar form factor), but is in fact a multi-turn planetary drive device. As can be seen from the back, there are three ball bearings at the rear. The shaft drives against the inside of the balls, rolling them and causing them to 'walk' around the inside of the outer housing. The bearings are held in a plastic carrier that turns with them as they walk around the inside of the shell, but due to the reduction factor of the small shaft turning the much larger ball bearing, and the further reduction caused by using the motion of the ball bearings as they walk around the shell, you wind up with a multi-turn pot capable of decent resolution in a package that's not much larger than that of a standard sized one, and with a relatively simple mechanism that does not require teeth or finely pitched screws, It's entirely friction driven. The rear of the pot is visible on the left side of this photo:A different view showing the planetary potentiometer:As with everything of that era, it is an interesting exercise in packaging to see everything arranged and laid out so as to fit in the limited space available.-Pat

author: bitseeker
author_rank: Super Contributor
timestamp: July 07, 2016, 03:50:47 am
content: Thanks for the tour, Pat! Really nice module you got your hands on. I also like your green & gray tower of power (there was a more revealing shot of it in the lab thread).

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 07, 2016, 06:55:54 am
content: Pat,that's a beautiful device, thanks for sharing all these pictures.The manual can still be found online at Keysight.com.The voltage reference looks like the Reference Amplifier type, i.e. realized by transistor Q4 and zener diode CR6.In your unit, this reference assembly already has been potted inside this black, round plastic part on A6.Is there a type designator and manufacturer on it? Maybe Motorola?THXFrank

author: Cubdriver
author_rank: Unknown
timestamp: July 07, 2016, 07:58:20 am
content: Frank -Thanks, and my pleasure. I enjoy getting a look inside these things, and might as well document the journey while I'm there. (Plus it gives me an excuse to play with the camera, too.)I plan to post more of the pics, just ran out of steam tonight.I was able to get a hard copy of the manual for it (can't beat those 12' long fold out schematics and drawings!); unfortunately it's an earlier iteration (serial numbers 410-, 448-; mine is a 0912-) so it isn't an exact match. Q4 & CR6 are the reference, and yes, they are potted in the large black can. (My older manual shows it as a TO-5 metal can, the same size as Q5, 6 & 10 nearby.) It is indeed a Motorola part, marked 1820-001 with a date code (I'm assuming...) of 7020. It has four leads; they are marked B, C, E and A for the transistor leads and anode of the zener. I'll try to get a better pic tomorrow or Friday.-Pat