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Flight of the Pheonix

Posted 26th April 2012 at 08:34 AM by rjm
Updated 4th May 2012 at 02:30 PM by rjm

Nor the remake, the original. Good film. Story shakes out something like "Twelve Angry Men in the desert": Put together a small, random group of people and pressure them to complete a task. In the case of "The Flight of the Pheonix" this is to make an airworthy plane (this one) from the crashed remains of another (this one).

So. We start with my old red Gainclone case, and a pair of these buffer boards , and a Takman resistor, 24 position stepped attenuator from eBay, unassembled, and start working to transform something old into something new.

Here's my LM3875 gainclone. Served me well, but it is time to bid adieu! (at least to the guts):
Click the image to open in full size.

Opened up, we see the circuit board, such that it is, and my home-built 11 position attenuator:
Click the image to open in full size.

The case is stripped, new parts waiting nearby. First though I have to drill a bunch of new holes.
Click the image to open in full size.

Holes drilled, attenuator built, chassis wiring completed, ready to zip back up:
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Finished, awaiting smoke test...
Click the image to open in full size.

Smoke test passed, but one channel makes a sputtering noise and its output offset voltage is erratic and high, about 1 V. Then it seemed to fix itself. Perhaps some residual moisture from me cleaning off the flux earlier. I re-heated some of the solder joints on the transistor pads just to make sure, and the problem has not recurred.

Click the image to open in full size.

All quiet and well-behaved now. Noise and distortion below the measurement thresholds of -115 dB and -90 dB respectively.
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