Elegant vintage HP VTVM -

[goodfellow]

One of my pride and joy finds -- HP made some really beautiful test equipment 50 some years ago.
I came across this HP412A DC Vacuum Tube Volt-Meter (VTVM) a few years ago. As the name implies, a VTVM has vacuum tubes (hence it needs external power) that are used as an amplifier. This design makes this instrument much more sensitive than a traditional Volt/Ohm Meter (VOM) when diagnosing very low level resistance and voltage readings in a circuit. For working on my old Sun scopes --- these things are the "bomb".

One of the most interesting aspects of this meter is the the AC powered photoelectric "chopper" circuit that cleverly synchronizes the modulation and demodulation of a DC signal to provide a super accurate reading of VERY low voltages.

Today we can do much of this with cheap Integrated Circuits, but in 1965 HP did it with awesome engineering and very expensive modular components.
The pics show the small array of 4 light bulbs that are positioned over the AC powered photoelectric chopper circuit

I bought this thing at a HAM swap meet for a few bucks. It's pretty sophisticated for my limited knowledge, but I managed to get it back in working order and refurbish the exterior as well. My father had one of these in the 1970's and it was his "pride and joy" -- in 1965 it cost as much as a color TV. Here's to you dad!!!

















Finished it up and painted --

[J.A.F.E.]

Great meter.  HP made a lot of lab grade equipment and even in more affordable gear that technology found it's way in. The other advantage of a VTVM is the input impedance is for practical purposes infinite.

[goodfellow]

Thanks Steve --  I'm always amazed at how much engineering and quality was built into equipment before the globalized economy built everything to the least expensive standards.

[J.A.F.E.]

Some years ago I was working at a job where I needed a really fast oscilloscope and only Tektronics and HP had anything but they both had exactly what I needed. I was speaking to one of the reps and commented that everytime I needed something really fast or super accurate one or both companies had what I needed. He said the reason was (at the time anyway) they made instruments for the military who was 10-15 years ahead of the civilian world and most of that stuff was classified. By the time the civilian world caught up the stuff was old enough to be declassified.

I think that mindset went along with making quality stuff and while things are always cost sensitive it was anticipated to be expensive and in exchange it was expected to be high quality, durable and long lasting.

Now things seem to be make it as cheap as possible, give it a limited "design life" (ie planned obsolescence) and provide the minimum.