This board, with the nuvistor, is loose. There's no mounting hardware that I can see. There was a bunch of decayed foam in there, too. Does anyone here have a 3400A? I'd like to know how this board was secured in the meter.
It was embedded in foam plastics to fight the microphonics of the nuvistor. The board should not have any solid contact with the chassis. I cut a slit in some foam plastics and placed the input amplifier board in it:
- Thomas
Thanks for the video link, Thomas. The arrangement makes a lot more sense now.
Having dealt with a number of similarly mounted vibration-isolated microphones, I suspect that the weight of the board has caused the bottom side foam to compress to a thin film or it has crumbled to a fine powder and blown away. The gap above the board in yours indicates that is probable. As does the video from Thomas, of course.
Do not consume orally.
The foam has been transformed into a pile of crumbs, liberally distributed throughout the interior of the unit. Before I worry about microphonics, though, I am going to figure out how to apply power to see what other problems there might be. If it doesn't power up, for instance, dis-assembling it to remount the board in foam will become a
low priority item.
That said, I love the look and feel of these old HP meters, even if they are not practical enough to rank space on my very tiny bench. So if I can get it running, I will, though I will probably try to sell it rather than keep it.
And Thomas, thanks for sharing the photo, too.