Thanks everyone for your comments.
This plugin was an interesting mix of tube and transistor circuitry. I think it is one of Tek's first attempts to use transistors in their instruments wherever possible.
It certainly uses some early Ge pnp transistors in less critical areas. The lowest 2N number in it is a 2N270 which is an emitter follower for the shift voltage applied to one side of the vacuum tube differential output amplifier. The multivibrator transistors were 2N1377's and the trigger amp is specified as a 2N1631 which had been replaced with a AC128 which is a lot slower but seems to work. All the tubes in the plugin were OK despite their age.
The "magic" in this plugin is contained in the mercury wetted relay sealed inside the glass vial. I not so sure it is pressurized.
It is pressurised and both the S and 109 manuals warn about the explosion risk. The 109 manual mentions the limited lifetime but not the S. I checked the Tek part numbers in the manuals to see if they used the same part and it was indeed the same one. It would have been an interesting challenge to try to make up a substitute fast rise pulser using modern parts if the reed was faulty.
I switched on first time my "R type" plug in which measures transistor risetimes.
I have one of these too. I last used it to check the transfer times of optocouplers I wanted to use to transfer video pulses to a CRT grid.
Even though the unit seems to work well there are some glitches and I suspect some of the precision resistors in it have drifted over the years. Replacing them will not be easy and I might not do it at all. Where does one find a 43.4K or 69.5K precision resistor these days?
Cheers,
Morris
