KA-116: oscillator's coil & power transformer

Construction of the oscillator's coil

The coil was made after carefully analysing the photos of the original coil. From this photo the number of turns, and dimensions were estimated. The separation between windings was set to be 3mm.

Coil form: Made of PVC; Outer diameter: 3,0 Cm.; Length: 4.5 Cm.
Grid coil: 5 turns, of No.25 enameled wire. Each, turn separated from the next one, by a blue silk thread.
Reaction coil: 7 turns, close wound of No.20 enameled wire. Placed between both halves of the grid coil.
Note: The grid coil and the reaction coils are wound in the same direccion.

Results
When this coil was used with a variable condenser of 500 pF, its resonance varied, from about 4.5 MHz to about 13 MHz, as indicated by my Millen GDM. However when the converter was tested, the oscillator stopped working just below 7 MHz. To correct this problem 5 turns were added to the reaction coil. Because of the added distributed capacitance, the oscillator's range became 4.5 MHz ... 11.7 MHz. A perfect range!

In some cases this correction may not be needed, because the functioning of the oscillator, also depends on the type of tube being used, and the working voltages of the circuit. Therefore some experimentation may be needed.

Construction of the power transformer

This transformer was hand-made by my friend José Luis Argueta. It is wound on an old Philips iron core. Under actual use it produces the following voltages:

250--o--250 AC volts
3.94 AC Volts/3 ampers. Needed voltage 4.0 Volts AC!
2.81 AC Volts/2 ampers. Needed voltage 2.5 Volts AC!

This transformer can be seen below. (Click on images to enlarge)

Assembling the KA-116

The construction of the KA-116 may be appreciated in the sequence of photos shown below. (Click on images to enlarge)