The small mercury thermometer with electrical contacts was common in such fixed temperature applications for some time. It was a very repeatable set point controller. The small heating coil at the 'top' end of the thermometer was probably to make sure that end was hotter than the other end in the pocket coupled to the main heat sink to prevent condensation of the mercury away from the main column connected to the bulb. These thermo switches could provide 0.1degC repeatability over long periods as long as the switched current was very low. The relay was probably driven by the transistor that switched off when the mercury contact was made. The other half of the oscillator box with the trimming capacitor and second transistor was probably a circuit similar to what you had in the schematic just with different pin-outs. There is probably very little to work out. Power in for the osc, the heater and the frequency out. Perhaps some indication that the temperature set-point had been reached once or recently.
I would love to see a full restoration. The power supply should be easy to fix, but the rest of it looks pretty daunting if it's not working, and calibration could be tricky if you don't have a procedure. At least there aren't lots of wax capacitors to replace.
Very nice construction here! Reminds me of Rohde&Schwarz equipment from 60-70's. The non-magnetic plates are maybe brass (silver-plated?) I dis-assembled some R&S "Sichtzusatz zum Videoskop" for a TV transmitter which had similar hi-quality construction several years ago. But- a 7490 TTL divider from 1965? Really? They used both state-of-the-art semiconductor components as well as proven tube technology apparently. The diode quad is a ring modulator/ balanced mixer
The small mercury thermometer with electrical contacts was common in such fixed temperature applications for some time. It was a very repeatable set point controller. The small heating coil at the 'top' end of the thermometer was probably to make sure that end was hotter than the other end in the pocket coupled to the main heat sink to prevent condensation of the mercury away from the main column connected to the bulb. These thermo switches could provide 0.1degC repeatability over long periods as long as the switched current was very low.
The relay was probably driven by the transistor that switched off when the mercury contact was made.
The other half of the oscillator box with the trimming capacitor and second transistor was probably a circuit similar to what you had in the schematic just with different pin-outs. There is probably very little to work out. Power in for the osc, the heater and the frequency out. Perhaps some indication that the temperature set-point had been reached once or recently.
I would love to see a full restoration. The power supply should be easy to fix, but the rest of it looks pretty daunting if it's not working, and calibration could be tricky if you don't have a procedure. At least there aren't lots of wax capacitors to replace.
Very nice construction here! Reminds me of Rohde&Schwarz equipment from 60-70's. The non-magnetic plates are maybe brass (silver-plated?) I dis-assembled some R&S "Sichtzusatz zum Videoskop" for a TV transmitter which had similar hi-quality construction several years ago. But- a 7490 TTL divider from 1965? Really? They used both state-of-the-art semiconductor components as well as proven tube technology apparently. The diode quad is a ring modulator/ balanced mixer