Part 2 – Testing the Transformer

In Part 2 of this series, I’ll check out the transformer in the tube tester.  This is the heart of the unit, and if it is not good, then the project will be scrapped.

Test Locations for Filament Readings

Filament Selection Actual Voltage
0.75 0.77
1.40 1.54
2.00 2.11
2.50 2.69
3.30 3.46
5.00 5.18
6.30 6.74
7.50 7.88
12.60 12.87
25.00 26.58
30.00 33.66
50 – 60 52.60
70 – 80 73.70
100 – 115 115.20

As you can see, the filament windings all appear to be intact.  Most are reading a little high, as would be expected with no load.

12.6 volt filament reading – no load

Next is to check the high voltage windings – 30v, 100v and 250v.

For all three of these, the common lead is the right hand lead of the Plate Voltage potentiometer. The one with the red lead soldered on it.

For the 30 volt winding, the red lead connected to the Type switch, below is the other lead connection test point.

Test Points for 30 volt winding.

This lead read 29.94 volts AC.  Good…

The next lead to check is the 100 volt winding.

100 volt winding test points

This is checked between the common lead on the back of the Plate potentiometer, with the red lead, and the right hand side of the big yellow capacitor, with the other red lead.

This winding read 99.9 VAC. Good…

Finally, the 250 volt winding is checked between the same common lead on the back of the Plate Potentiometer and the second lead, attached to the end of the large resistor right next to it, with the other red lead.

250 volt winding test points

This winding read 249.4 volts. Good…

So it looks like we can continue with our restoration.  The transformer appears to be in good condition.