Where is the grass greener? In Philadelphia, or in Gdańsk? @FranLab just posted a video of the Grass Instruments P511 amplifier - https://www.youtube.com/watch?v=St_wtPv85Mc This reminded me of the little treasure I once got from a lab clearance at the Gdańsk Medical University (GUMed), also made by Grass Instruments, but older and almost totally tubular, save for detection diodes. I was going to make a video about it for a long time.

It's the SIU-4B stimulus isolation unit. It was used either in electro-medicine or biologic research, and provides galvanic separation between waveform generator and the patient or test subject.

A beautifully built little device with a single vacuum tube Hartley oscillator driving a transformer used for galvanic separation between the equipment side and patient side. The high amplitude AC signal applied to the tube's plate modulates the radio frequency signal passing through the core-less HF transformer and then is demodulated, filtered and attenuated, optionally with phase inversion. Perfect simplicity, astonishing build quality! It's built on a 2.5mm (or .1" a.k.a. 100 mils - if you stick with Vader and Emperor Palpatine) thick glass-epoxy substrate normally used for making printed circuit boards, only this is not a PCB - it has no traces. It's a turretboard, not unlike those found in boutique tube guitar amps. A thing of beauty, a joy for ever. I'm keeping this loveliness as a museum piece for the future generations to see and be inspired by.

0:00 Intro 1:41 Touchyfeeliness 2:15 Front Panel 4:05 Taking It Apart 4:45 Look At These Lovely Parts! 7:13 Aftermarket Mod 8:10 Schematic 14:37 Enclosure 15:10 Medical Electronics Commentary 16:55 Afterword

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