An HP 400L VTVM found its way into my collection of amusing, anachronous test equipment.
Click for larger view
It came with the operating and service manual, which was printed in 1963.
This VTVM measures AC voltages in twelve ranges - .001 VAC to 300 VAC, Decibel range -72 to +52, with a frequency range of 10 cps to 4 mc.
It weighs about 18 pounds, or in terms of our cat, 1 Chester Unit.
1 Chester Unit
Unlike a lot of old stuff, this came with the original box. It had been sitting on a shelf, unused, for decades. It is exceptionally clean, so I don't have to deal with rust, dust, or other annoyances.
What's Inside?
The following two images show the jumble of parts.
Left interior jumble...
Tubes!
First up...
Never plug-in and turn on old junk like this. Yikes. Since I dislike refinishing metal and all the cleaning, this is a nice project to work on. To make it operational, I will replace the electrolytic capacitors, a few Bumblebees (another common old capacitor type) and other random components as I check out the circuitry. Unlike the Hallicrafters restoration (see the previous project), I will use modern multi-section electrolytic capacitors.
The Suspects...
Bottom of multisection capacitor C1, with associated resistors
I will take several pictures of each component prior to removal. Each part directly connected to the capacitor will be checked out-of-circuit. There are no tell-tale bulges or evidence of heat stress in this area.
Selenium Rectifier
I will research the need to replace this selenium rectifier - I vaguely recall some post in another restoration forum about these things.
Getting the Stuff Together
Which meter to use...
I was too lazy to look for the test leads for the tube-based Simpson 303. Is it a shock (so to speak) to imagine I have two of those? Not pictured - the Weston 931...
Solder, desoldering stuff...
The Powerstat - to gently ramp up the voltage for testing - in a few weeks!
Next: Deciding where to start.
