Crawls Backward (When Alarmed)

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SDS Power Supply Board - Anything But Boring in our PAS

Next up is wiring up the new SDS power supply board.  You may recall I built the board back at the beginning of the project.  Now we're a-gonna install it.

There are two terminals on the board which are labelled "blue" and these are for the 12 volt filament line for the 12X4 rectifier tube.  This line also goes to the pilot light and it is also rectified by the two diodes on the board and filtered by the two 1800 uF caps for the 12AX7 tubes to run on DC instead of AC.

On the original PAS, the blue leads go to the lugs on the selenium rectifier and are connected to a twisted pair that go to the 12X4 filaments.  There really isn't a provision for this connection on the SDS board, so I just ran the two blue transformer leads to the board, and then connected the twisted pair to them.  Not the way I would have preferred, but it's secure and should work ok.

Then it's on to the rest of the wiring.

On the right side of this picture, you can see where two twisted pairs exit and go to the PC-5 and PC-6 boards.  One pair is black and one is red and black.  These are the DC filament lines.

On the left side, the two black leads are from the AC line - they run to the fuse on the top of the board.

And the two red leads are the two B+ lines that go to terminal #16 on both the PC-5 and PC-6 boards.

With the wiring done, we can bolt the SDS board down.  I was concerned about putting it too close to the chassis and possibly having something short out, so I mounted it as you see here.

I have a #8 x 1 inch bolt coming up into the chassis with a nut holding it secure.  Then I have another nut 'suspended' near the top of the bolt.  The board rests on this and there is another nut on the top holding the board down.  Not a real fancy mount, but it's really just like the original PAS mount, only a bit shorter.

Finally, here's a shot of the under-chassis wiring.

You can see the two twisted-pair filament lines going to each PC board.

On the left is a small hole where the two B+ lines come down and then run to each board.

The red wire on the right is the rectified DC off the cathode of the 12X4 - it goes up to the filter board.

I put grommets on the two smaller holes so the insultation wouldn't chafe on the chassis.

For some reason, maybe it's just the sheen of the metal, but all my shots of the chassis are a bit hazy looking.  Need to investigate why the camera is doing that.

 
 
 
 

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