Maker Pro
Maker Pro

Sencore PR57 isolation transformer (missing button / missing probe)

TomB19

Dec 21, 2021
28
Joined
Dec 21, 2021
Messages
28
Mods: I apologize if this sort of content is not appropriate in this forum. Please move or delete as needed.

I got a good price on a Sencore PR57 Powerite isolation transformer. It had some minor physical damage, was missing a button, and also missing the probe. Still, it is a beautiful instrument and was not difficult to put into perfect working order. I look forward to using it for many years.

The metal work was pretty boring. I just bent the case back to where it needed to be with my fingers. It took about 30 minutes. I try to error on the side of doing less, when working metal. It turned out perfectly. No one would know it had very minor case distortion.

The missing button was the "lo side" leakage button. The 3d printed replacement doesn't look quite right but it is surprisingly not that noticeable and feels the same as the others in operation. Fortunately, the switch was undamaged.

PR57 face view.jpg

I made the probe from two resistors (100K + 33K), a leaf switch from an arcade joy stick, and a butt connector to connect to the probe element. It's all inside of a Princess Auto 12v test light.

The resistance does not meet the 135K ohm spec but I can make it reach full deflection on the scale. A bit of testing shows that it works correctly.

Switch assembly.jpg


Here it is together. 3d printed parts were used to wedge the switch into the interior taper. There is also a 3d printed button and a tiny yoke, to hold the button to the top leaf switch blade. The leaf switch mount is a taper so it is a wedge fit. The button is held in place by the spring action of the switch. Super simple.

finished 1.jpg
finished 2.jpg

All of these 3d printed parts will be on Thingiverse, in the next couple of days.
 
Last edited:

TomB19

Dec 21, 2021
28
Joined
Dec 21, 2021
Messages
28
For what it's worth, I picked up a Chinese, isolated, variac that was so lousy, I returned it. That device was more expensive than this old, damaged, PR57 but they are not in the same league. Even for a hobbiest, the Asian variac was pretty crap. This Sencore instrument is beautiful to use, the gauge is accurate, and it has wonderful build quality.
 

73's de Edd

Aug 21, 2015
3,437
Joined
Aug 21, 2015
Messages
3,437
I find that true on all of the Sencore "stuff" .
Alas, with the necessitation of sacrificing that olde tyme, treasured leaf switch . . . . . .you can no longer be a " Pinball Wizard" . . . . a la Elton John.
 
Last edited:

73's de Edd

Aug 21, 2015
3,437
Joined
Aug 21, 2015
Messages
3,437
Your shown craftmanship doesn't suggest, and shows naught of those conditions.
That's a NICE super-springy black 'nanner plug there . . . . . I only dislike it using the side screw.
 
Top