The AM Forum

Here is a board, we have several of them.

Tubes are 6AU6WA, 6AU6WA, 6101/6J6WA, and 5814WA. 

They were all wrapped on what looked like original paper wrapping (gone now) appearing to never have  been used.
On the front of the board is "H/P 285525 ASSY" and on the back "285526".

I'm sure these are a replacement board for some cool instrument but which one of them?  8-) that is the riddle. These are too nice to just lay aside. I hope they might be good for some gain in audio or VLF range.

Well it doesn't look like anything military. It could be some type of early computing but since it has a 6J6 in it, that throws a curb since they tube can operate in the UHF area.

I worked on electronic organs, almost all brands but it doesn't look familiar for that. One other possibility would be a board for an oscilloscope?

I started the schematic but it is very tedious. Could be from a scope and looks to be ac coupled. Maybe alternately  board from one of those old frequency counters? 

I had a few of the early counters and don't remember seeing any boards like that.  My guess is a scope but I had a lot of the early scope also and don't remember seeing that board.  Maybe one of their chart recorders.  HP made of lot of stuff.

I was able to ascertain a vague reference to an H-P Bigfoot???

However, when trying to find out what that might be I ran into every 2and 4cycle motor imaginable that had been called a Bigfoot  and it's horsepower rating.

So, hope that might help.

--Shane
KD6VXI

Wow, tubes on circuit boards!  It's like a primitive surface mount device.

I haven't pulled apart any tube gear (other than ham stuff), so that's new to me. I thought everything was all point-to-point stuff with those Radio Shack style wire terminals. 

I need to get out more.

Jon

Virtually all the last generation of all-American five plastic cased table radios had printed circuit boards along with a piece of glued on aluminum foil above the 50C5 and 35W4 on the underside of the case top.  Components around those two tubes always had a baked or burnt look as well as the board around them.  ;D. Metal chassis were long gone; the board mounted on slots in side of cab.  They may not even have wasted a good ferrite core on the antenna coil, just a printed circuit wire loop on the inside of a quasi cardboard cab. back.
Popping that out for service ( no screws, just plastic tabs) generally cracked the cabinet if it was heat hardened.

Even Dynaco, a well respected audio outfit made audio amps and preamps with tube printed circuit boards,  as well as Heath Co. for audio, metering and RF applications.

Detroit went through this phase too until the Japanese produced better quality cars. Doors and hoods with 1/4 gaps, no alignment an routine breaks in every component. In the case of electronics of course, the American manufacturers never recovered.  Early auto imports had easily rusting bodies, but they quickly realized that Americans generally used salt in winter and corrected that problem.