Almost fully populated board tested with adequate transformer I received today

 TRANSFORMER ARRIVED TODAY BIG ENOUGH TO TEST ALL LAMPS AT ONCE

I had ordered at 6.3VAC transformer rated at 6A, which is big enough to handle the 7+A of the full board for short periods. I wired up the primary to a plug, popped it into the wall and verified the voltage of the secondary was 7.6 VAC; a bit hot but even better as a test since it draws a bit more current than we will in the running 1130 system.

Transformer rated at 6A

Wiring the transformer to the board was next on the task list - tying one side to the common of my 3V DC supply while I was at it. A quick activation to ensure nothing bad was happening, and then I could turn on the Lamp Test switch.

LAMP TEST WITH 150 BULBS INSTALLED (OUT OF 164 POSSIBLE)

Due to a shortage of bulbs, until the new supplies arrive, I didn't have bulbs for every position. I got close, illuminating two of the Synchronous Communications Adapter (SCA) positions but leaving the rest of the SCA and all of the Customer Engineer (CE) positions empty. Every other position that is active on an IBM 1130 had a bulb in place.

I flipped the Lamp Test switch, which injected +3V to the control line on the board that caused all of the thyristors to conduct and illuminate their bulbs. Prior to this I had hooked up three random signal inputs to +3 just to have a brightness to compare against. The result was a bit of dimming but the transformer voltage sagged less, only down to 5.76V. I could see the current jump up initially then drop to just under 6A. As I added in the last few rows of bulbs, the final current seemed to have settled to that same level suggesting that the transformer is saturating.

Lamp Test mode

Comparison of three bulbs fully lit

The board remained cool to the touch, as did all the thyristors and the wires bringing the AC current onto the board. I left the Lamp Test switched on for quite a while, with everything remaining as it was. I am now happy to consider this board fully tested and ready for its eventual connection into the IBM 1130 computer. 

Current with three bulbs lit, full voltage delivered

Current with 147 bulbs lit, noticeable sag in voltage