Some Experiments on the Amplification of Thermocouple Electromotive Forces

Experiments employing a new type of regenerative direct-current amplifier have shown that such equipment is unsuited for use, except, perhaps, in the laboratory. A successful system of amplification employing vacuum tube amplifiers and commutators for inverting and synchronously rectifying the resulting amplified alternating potentials is described. Thermocouple electromotive forces less than 10−9 volt are readily indicated on a portable microammeter. The over-all useful amplification with portable equipment exceeds 50,000.