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lunedì 23 marzo 2015

My next regen receiver - Almost completed

This is number four of a series of posts about my new poor-man regen project. Previous posts (ordered from older to newer) were:

My next regen receiver - The power supply
My next regen receiver - The AF amplifier
Quick test of the AF tube amplifier module

Now I have completed the build with the RF stages (an untuned amplifier based on a 6AK5 tube, followed by a regenerative detector based on a 12AU7 tube, wired as a pseudo-tetrode).

The RF part of the design was copied from David Newkirk's Receivers for Watching 7120 kHz, with only minor modifications that I will describe in a schematic diagram as soon as it will be stable enough after some more tests and tweaking.

Overall, the layout and the mechanics look a bit "oddish" (it is a poor-man regen, as I said). For the chassis, I used two pieces of copper clad and some pine wood. For the back panel, I cut a small rectangle of galvanized sheet and for the front panel I used a piece of aluminium sheet which was part of a dismantled surplus equipment.
My very first tests seemed encouraging: with 1-meter long antenna wire I managed to hear quite strong european broadcast signals, in a shortwave band that I couldn't identify (I have still to make a rough calibration of the tuning range/scale).

Some images follow of the receiver as it looks at present. Next post on the same subject will include the schematic diagram and a short video clip showing the radio in operation (hopefully :-)).

The coil is 22 turns of AWG18 enameled copper wire over a 1" 1/4 support.
The Hartley tap wss provisionally set at 7th turn (about 1/3) from the ground side.
The grey (shielded) cable goes to the AF gain pot and the black one is for the AF output jack.

Another view with the main tuning variable capacitor (Hammarlund, 140 pF per section).
Mounted above on the front panel is the band spread capacitor which has an embedded 1:3 reduction drive.

The back panel has inputs for the 6,3 VAC heaters voltage and for the 150 VDC B+ voltage.

The front panel (without knobs). From left to right, top to bottom: AF gain control,
band spread varcap, AF output jack, main tuning varcap, AF output switch (speaker/headphones),
antenna input, RF gain control, regeneration control.
The hidden side, with wiring.

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