A Tribute to HP Test Equipment Power Switches
By Roger Arrick

See Steve Noll's giant list of test equipment dealers
Visit TestMart - The Global Test and Measurement Center

Those who have owned multiple pieces of HP test equipment have laid in bed many a night pondering the great mysteries of front panel design. HP, known world wide as a producer of quality test equipment for decades has lead the way by suppling our imagination with a never-ending variety of power switches (or would that be line switches?). Here are just a few examples of this cosmic conspiracy of power switch inconsistency.
Feedback to roger@robotics.com

---

3455a System Voltmeter This white square push-on/push-off button can be found on many pieces from this era. In this case, it's labeled "LINE" and has no power light.

651b Test Oscillator Vintage HP in the older grey color. This robust toggle style switch lets you know who's boss. No accidental power-off here. This one is labeled "LINE" and has a small square power light above.

3586b Selective Level Meter This giant gets a push-on/push-off which is a little bigger than others. Notice the label "POWER" right on the switch with the words "STANDBY ON" written above. No power light.

1645A Data Error Analyzer Vintage but with the newer "puke-green/beige" color. I'm sure there's a real name for this color but everyone I've talked with calls it "puke-green something another". As for power control, we're in for a real treat on this one. A giant round push-on/push-off with an integral lamp and the word "LINE" written above.

8903b Audio Analyzer I admit this is my favorite piece of equipment. Very useful for a music synthesizer builder like myself and very easy to operate. But I always fumble a little with it's power switch. Take a close look - it's a small plastic rocker labeled "LINE" with "ON" and "OFF" positions labeled. Oh, no power light on this one.

3437a System Voltmeter This high-speed beauty has measured many an electron and it's power switch sticks out a little more than others of it's style for some reason. This plastic square model is labeled "LINE" and beige in color.

5180a Waveform Recorder This is a nice unit but I still don't know how to use it. That's what I get for bidding for something on EBay I've never seen before. (Walter, where are you when I really need to get out-bid???) Anyway it's got a cool power switch. A long thin push-on/push-off model labeled "POWER" with positions labeled "STANDBY" and "ON".

5328a Frequency Counter What in the world is this? A normal toggle switch? Let's get it together folks!

3582a Spectrum Analyzer Ok, I changed my mind, this is my favorite piece of equipment. Every once In a while I rent a forklift and move it to a different bench so the carpet can get a rest. Anyway, you'll notice the familar square push-on/push-off power switch but this one is a different color than most - light beige.

5335a Frequency Counter This looks normal enough right? Nope, it's got a little standby LED off to the side. It stays on all night and allows me to use my home office with the lights off.

5005b Signature Multimeter Ok, we've seen the little rocker switch before, but this one is SIDEWAYS!

654a Test Oscillator Now check this out. It's a toggle but has a strange black plastic handle.

8018a Serial Data Generator Ok, another push button, but this one is different than any other. A wide square with a "LINE" LED above.

Stack-em! Uh, I'm not really sure why, but something tells me to stack this stuff as high as possible....strange huh?

The End Have you ever looked at the rear of these things? Every one has a different fan, some have different fuse holders, different address switches, different power cords. Will this madness ever stop!!!!!

Alex C. writes
I just want to say that you have barely scratched the surface! What about my HP 1715A o-scope with the little multimeter perched on top (built on)? It's got a on/off switch on the multimeter itself, with no indicator light, then the 'scope itself is turned on with the Scale Illumination knob, which has the little on/off legend and LED underneath it, where you can't see it unless the scope's at eye level or higher, which mine isn't. Aargh! HP equipment is cool and as far as I'm concerned, every square inch of it is fascinating. Think about it, there are engineers at HP who *designed* those power switches. They're even more psychologically wound up in them than *we* are.

John M. writes
I have to admit I'd never really thought about H-P power switches before - you've really opened my eyes to the possibilities of this fascinating subject. My H-P 312B has a power switch similar to the 654A Test Oacillator, but it's mounted sideways at the bottom center of the panel. I seem to recall the 312A had a lighted (red) push-button switch in the same location. Why did they change? I guess it'll always be a mystery.

David D. writes
Very amusing, but you've only scratched the surface. There are all sorts of rotary switches too (especially on battery powered units, e.g. 3580A). As far as stacking goes, you're lucky you don't live in an earthquake zone! That 3582A could turn on you!

Larry P. writes
This is a fascinating study. Oh, by the way, my 5328a has a small black plastic slide switch to control AC power and no LED indicator. Now for something completely different...have you noticed how many pieces of HP test gear have the same meter? 2 and a quarter by 4 and a half inches. And the ones that aren't exactly this size still have a 2:1 aspect ratio.

Mark K. writes
Power switches: Very cool. You neglected one. Check out the mid 1960s power switches like the 8405A power switch; push on, knurled nut. Best wishes from a test equipment fanatic...

Walter S. writes
I am still laughing from the "tribute to HP power switches". God, I thought I was obsessed with test gear, clearly I have a ways to go to catch up with you!

Roger's response to Walter:
Thanks for the comments Walter (I think?) But if you outbid me again on Ebay I'll have to start breaking things. :)

Tom V. writes
That's a really nice web page. I had a good laugh - and it looks a lot like my lab. I've had similar observations about HP instrument design. My particular interest is in the displays HP used over time for their counters - from 1-of-10 neons, to various sizes of Nixie, 5x7 and 7-segment LED, LCD, CRT, VFD, etc.

Alexandra L. Carter
Ever wonder what happens *behind* the switch? Not the regular HP stuff, the spectrum analysis, multimetering, etc. I mean, where the *switch* goes! Here are a couple of images of a seemingly innocent HP 3468B multimeter I got recently, that simple little switch on the front isn't as innocent as it looks, that sneaky little botton snakes all the way nearly to the back of the instrument where the actual *switch* is hiding. Sneaky.