Altec 535A power supply for 458A / 459A / 250SU

[emrr]

Going through some of the amps and looking at a couple of these unregulated PSU's.



complete manual:
https://groupdiy.com/threads/altec.44774/page-2#post-1041174
I appreciate the reality factor of a tapped primary adjustment to cover a 2 to 1 range of loads, to be sure filament voltage is correct for the number of amps used, with the note that B+ "should fall in the range of 250-300V, the exact value is not critical".

The use of a circuit breaker rather than a fuse is curious; why not a fuse?
I don't immediately see anything on the market now that is the same as this one:

Type A, 2.5A operate, 3.5A break

 

[emrr]

Old school Altec grounding instructions assume directly grounded racks, console frames.

These filament and B+ grounds are chassis connected in the 250SU console with no path back to the PSU, instructions NOT to add additional ground.

No one really grounds chassis via rack frames (telco style) anymore, and blindly following the instructions today would leave floating negative voltage references at the console chassis.

In my case I'm adapting a next-gen 250T3 console for the tube modules, which requires changing the power connector wiring.
I'm initially going with:
filament and B - terminals tied directly to PSU chassis
console chassis tied to B-

Reasoning to keep fil and B minuses tied to chassis at the single point in the PSU, separate on the path from console to PSU. Chassis to the lighter B- current path in the console.

Would you do it differently?

 

[emrr]

Illustrative of the realities of voltage losses in wire runs, with a 6 amp filament and 140ish mA B+ load, 118.2VAC in gives 7.07VDC at the PSU, and 6.64VDC 7 feet later. 265VDC B+, lowest primary tap. This should really have another amp module or two loaded in the console, as it's below the expected 2 to 1 load range, then, filament voltage loss in the wire run will be greater with the increased load.