Brown & Sharpe 961 gage amplifier and readout teardown

[rhb]

I can't find *any* information other than a not very readable scan of a few catalog pages.  So not much else to be done but take it apart and figure out how it works and why it won't work with the sensor I have.

For those not familiar with these, they are used with variable differential transformers to measure very small displacements though this is only a 10 millionths readout.

It's very high tech.  It uses 7 Telefunken AF 101 PNP Germanium transistors.  One for the oscillator and 3 for each channel from the secondary.

So here it is laid out on the bench waiting to be probed.

[beanflying]

Try hitting up Robrenz here or via youtube maybe. He does have a slightly newer version of yours and might have a few clues to add or where else to look?

I also did a trawl of VintageMachinary.org and nothing there apart from an even earlier one shown in a Catalogue.

[rhb]

I'm looking for a 1021, but thought this was worth a go.  It's certainly a history lesson.  Lipton has a 961.  I've emailed him but haven't heard back yet.

I discovered it's got 8 transistors.  The PSU uses one wrapped in an aluminum heat sink as the pass transistor.  -13.0 volts with 2 mV of sawtooth ripple!   Using 1960 transistors.

Signal is at 10 kHz and it appears to use a full wave rectified 60 Hz transformer tap to gate the measurements to a single half cycle which passes the 10 kHz every other half cycle.  However, I'm mostly guessing based on probing the interconnects.  So things may be very different from what I imagine at the moment.

The photos show the PSU board.   AC input is next to the yellow wire and - 13 V at the other end.  I'm not going to do a schematic for it as it works just fine.  Besides, the circuit is so obvious you don't need a schematic.

I also know the oscillator is producing a 10 kHz sine wave.  Lots of harmonics, but looks OK on a DSO.  So likewise, I

The use of germanium transistors may make repairing one problematic, but it appears that an NTE  2N404 might work and even be an improvement.  Though if matching is required it would get painful $$$.

I'll add photos of the other two boards later.

Have fun!
Reg