Mystery Ebay amp purchase

[Pyre]

I bought this amp on Ebay for 20 bucks as it looked pretty interesting and I figured it must have 20 bucks worth of useable parts in it. Does anyone have any idea what this thing was originally used for? I can not seem to find much info about it on the internet. The thing is built like a tank and is labeled:

Microvolt Indicating Amplifier
Leeds & Northrup Co.
Philadelphia Made In USA
Cat. 9835-B

It is obviously some sort of scientific instrument. It has a 6X4, 6L6gc, 12AX7 and a 6072 under some sort of thick shield. There are two big cylinders plugged into tube sockets, one is a modulator of some sort. Unfortunately it is not a Illudium Q-36 that I can use to blow up the earth.

[smoking-amp]

Sounds like a chopper stabilized DC amplifier/meter for uV LF signals. The mechanical vibrating chopper converts the signal to AC, where it is amplified by the tubes, then re-converted back to DC by another chopper contact set. This scheme avoids the DC drift problem of a DC coupled amplifier. Likely was used for amplifiying the weak LF signals from strain guages, biological probes, capacitance / electromagnetic sensors,... Could be used for a making a milli-Ohm meter if you add a current source to it. Or put a piezo sensor on it for an earthquake monitor.

Don

[poynton]

What does it say on the chassis?



http://www.l-n-metprod.com/interior_h2.html

http://www.nuclearmarket.com/Supplie...?IDcompany=571



You could be correct about a sensitive 'chopper' amplifier - see link

[Pyre]

The only markings on the chassis are just the same as what it says on the front.

There is a 2 prong input and the output is labeled recorder. I think Don is correct in thinking it amplified a signal from some sort of probes maybe for recording purposes on a graph paper or something.

I like the earthquake sensor idea. I do not think there are too many earthquakes in Ontario though. I was going to pull the power transformer off and test it. It may work out well for a preamp power supply given the tubes that it powered.

cheers