"Frozen" Shafts on Variable AC Transformers`

Many years ago I had the luck to pick up several Variac (R) and Powerstat (R) variable AC transformers. They ranged from 5, 7.5, & 10A ratings.
 These were obtained dirt cheap because the wiper shafts were solidly frozen, and refused to move. 

Upon disassembly, I noted that every one had a thick grease lubricating the shaft.

I used a light hammer and a block of wood and a punch the same size as the shaft to VERY carefully drive the shafts out. 
  
It appeared that the grease used had caused the bakelite shaft to swell up, causing it to "freeze" in place.

Some work with DENATURED alcohol and some very fine sandpaper cured the problem. I washed the shaft 6-8 times with alcohol & let it dry out for several hours and did not re-grease it upon reassembly. I also very slightly beveled the very edge of the bakelite shafts to remove any burrs from the "brute force" disassembly and to make reassembly much easier.
   The one I kept is still working just fine after 45+ years.

NOTE: Please keep in mind that the amp rating of the transformer is rated across it's windings. So if you are trying to pull 5 A out of a 5A rated transformer, you MUST DERATE the current available at low voltages. 

NOTE NOTE: Variable transformers are of the AUTOTRANSFORMER design. THEY ARE NOT ISOLATION TRANSFORMERS.




When I started, I learned this the hard way on an AC/DC radio.

Nobody had explained the facts to me, as I was mostly self taught.


 I add an isolation transformer to the output (or input) of the variable transformer to isolate it, plus under fusing the input and output circuits. 


FAILURE TO ISOLATE THE TRANSFORMER CAN RESULT IN SHOCK, SERIOUS INJURY, OR DEATH.

 
TIP: You can often find an assembly of 3 variable transformers for 220 VAC 3 phase for almost nothing, as people don't want them.
 (220? Useless to me!).

 Just remove each variable transformer and you have 3 useable units. 
220? you say? Well they work just fine on 110V. 
You can, of course, also hook them to 220 if you want to.

 (I have all 3 of them and they are "only" rated at 45 Amps each. Cost? $5.00 for the set at a garage sale.)