[captainclock1988]

Hello everyone, the other day I traded an old Reel-to-reel tape recorder to a friend of mine who is also a fellow electronic hobbyist like I am for a couple of 1970s vintage HP Signal Generators, one is a Model 8640B and the other is an 8654B and they both came from a local high school that they used to use them for an electronics repair course they had there years ago that they just now got around to cleaning out their storage unit that had all of this old equipment in it that my friend was able to get his hands on these old signal generators.

Anyways these old HP Signal Generators have some strange quirks to them, the 8640B has an issue with an intermittent audio level control for the test tone so that when the unit is set to certain frquencies for the radio to pick up, the test tone is not audible unless you fiddle with the audio level control knob, the way the control acts, it acts like its a dirty pot, but when I opened up the signal generator, I took a look at the pot, and its completely sealed and there's no obvious way to get contact cleaner inside the pot, and the pot is held in place from the front with a nut and washer, behind two knobs that are held into place on the pot's shaft with one hex-head set-screw on each knob, and the set-screw takes a hex-key that is smaller than 1/16" and I'm not sure how much smaller than 1/16" it is exactly, as there's only two other sizes smaller than 1/16".

The 8654B signal generator has a broken u-joint going from the front panel knob shaft to the switch shaft for the display meter mode switch, and I'm not sure how I would go about repairing that u-joint, I looked over at McMaster-Carr and they do have u-joints for switches over there but I'm not sure what shaft size of u-joint I need, all I know is that the set-screws they used to hold the u-joints onto the two knob-shafts are hex-head set-screws smaller than a 1/16" and I unfortunately don't have any hex-keys smaller than 1/16" in my set of hex-keys. 

Any ideas as to how to go about repairing these signal generators, and what size of hex-key I need to remove the aforementioned set-screws?

[Mondial]

The hex key for the smaller setscrews is .050" which is the next smaller size down from 1/16".

[captainclock1988]

OK, thanks, I kind of wondered about that, I saw some hex keys that size over at McMaster-Carr.

What's weird is that I've noticed that the hardware stores like Ace, or Lowe's or Menards doesn't seem to carry hex-keys or drill bits under 1/16" and I'm not quite sure why, but they do sell them online through places like McMaster-Carr or other online sellers, why is that?

[mikethedruid]

You can get them in the big SAE & Metric set at Harbor Freight

[Mondial]

McMaster is where I get my small keys. I usually buy a few when placing an order for other stuff, as the tiny keys get easily lost. 

If you get to work on a lot of older HP and Tektronix test equipment, you will find that .050" and 1/16" are very common for the various knobs and shaft couplings.

[captainclock1988]

Ok, I'll check both of those places out. 

[Ron Ramirez]

As an aside, I just placed my first ever McMaster-Carr order yesterday - the rubber grommets I ordered were delivered today from their Chicago warehouse. I would expect you will receive service just as fast, since you are a lot closer to Chicago than I am.

[Simon Wa3uay]

I can vouch for Mc-Carr; they are almost always next day, even when ordering in the evening. Best of all, you can download 2D and solid models to use in your CAD assemblies, which is HUGE in the design engineering field!!
-Simon