Crystal Radio Output Transformer

The large size of the power transformer, used as an output transformer for my 'Loudspeaker 
Crystal Radio', was good enough reason to attempt homebrewing a relatively small one.

A search through the junk box yielded a 47mm diameter, Siemens N22 pot core set.

Pot Core used for Crystal Radio Output Transformer
Winding was for an autotransformer, having 500 turns of 30 SWG enamelled copper wire (the maximum number that could be accommodated), with output taps at 50 and 100 turns.
Crystal Radio Output Transformer - winding scheme
The 50-turn tap was to match the existing 3 Ω speaker and the100-turn one a provision for speakers of higher impedance.

A small PCB, also from the junk box, provided termination points for the winding.

Crystal Radio Output Transformer- inside view
A couple of reworked white plastic cosmetic jar bodies lent themselves as enclosure halves.

Crystal Radio Output Transformer
Tests indicated that, inspite of its small size, the output transformer's performance is comparable, though not equal, to that of the power transformer.

Related post: Makeshift Crystal Radio Output Transformer
_______________________________

Colourful Parallel-tuned Air-core Coil Crystal Radio

This is the colourful version of my 'Parallel-tuned Air Core Coil Crystal Radio'.

Colourful Crystal Radio
The coil is 75turns of hook-up wire, close-wound on a 2 ⅝" diameter plastic bottle, with a tap at 35 turns.

The 35 turn primary series-tunes the capacitive 60' wire antenna to resonance at 612kHz (frequency of the lone 200kW local AM broadcast station). The secondary is parallel-tuned using a 500+500 pF PVC gang condenser.

Colourful Crystal Radio - Schematic
The plastic bottle serves as the coil former cum enclosure. A screw-type terminal strip is used to connect antenna, earth and headphones.

Reception, using sensitive balanced-armature headphones, is quite good. Headphone current, measured using a 1mA FSD 60 Ω meter, is 400 μA.

Related post: Parallel-tuned Ferrite Toroid Crystal Radio
_______________________________