For nostalgia, I ran across these photos of a vacuum tube op amp that was used for recording earthquakes.

These amps were made by GeoTech of Dallas, Texas and date back to the late 50s or early 60s.

Not much use these days for actual seismological recording and if one of the tubes goes bad, "You're Outa Beer".

 

Neat, thanks for sharing.

 

That was well before the word "micropower" was invented (a low power amplifier being 10W), and you never poked you finger around inside the circuit to find an intermittent connection.
The only circuit board in sight in that circuit is a hard-wired vector type.
It has a DC balance control. That would imply that the amp was DC coupled(?).

 

I saw them when I was a kid in a Lear autopilot that took up about half of an ATR rack. This would have been 1956-57. Weight was the big thing for anything that went on an aircraft.

 

That was well before the word "micropower" was invented (a low power amplifier being 10W), and you never poked you finger around inside the circuit to find an intermittent connection.
The only circuit board in sight in that circuit is a hard-wired vector type.
It has a DC balance control. That would imply that the amp was DC coupled(?).

I've never seen GeoTech's schematic for this antiquated amp.

However, there was a schematic of a tube type op amp for seismic recording in a book published by Scientific American. It had two tantalum coupling capacitors on the output. The article also mentioned the tantalums cost about $10 each - which was very pricey stuff (about 1/2 a day's pay at minimum wage) in the early 1960s.