It was just fun!

The schematic diagram is here (regen_sch.jpg):

A version in better quality is here (regen.pdf):

It uses two 12AH7 double triode tubes. They just happened to be available in my junk box. The first two triodes work in a cascode circuit, where the very first one is connected in a Hartley configuration.

Regeneration is controlled by adjusting the voltage of the second triode's grid. When the regeneration control is at its minimum position, that means we have 0 Volts at pin 5, there is also no anode voltage at pin 3. The voltage at pin 6 is at its maximum then. When the regeneration control is engaged (voltage at pin 5 increases) the voltage at pin 3 also rises up. At the same time the voltage at pin 6 decreases, because the tube is drawing current and there is a drop at the 100k resistor.

The second 12AH7 works as a two stage audio amplifier. I tried to reduce the number of components to a minimum so, there is no cathode RC-combination in the audio stages. The necessary negative bias voltages are produced by the small grid currents flowing through the 10 MOhm grid resistors. With my 10 MOhm VTVM I can measure abt -0.65 Volts at the grids so, the actual voltage should be abt -1.3 Volts. There is no noticeable distortion of the audio signal. The coupling capacitors in front of the grids are quite small. This helps to reduce the hum. I tried an output transformer in an earlier version (you can still see the slots on the chassis where it was mounted). But this was a disappointment. So, it was replaced with the RC-combination (25k/1µ) shown in the diagram. Now I can use high and low impedance headphones. The low impedance ones sound much more "bassy".

The detector circuit was used in a receiver that was lent to me by a fellow ham in 1968 when I just started my amateur radio career. It was a kit sold by a German company (Technik-Versand Bremen) and worked perfectly well in those days even on the 10 meter band. I always regretted having given it back ;-) so, I wanted to build a replica now.

This works even better than the original. The sensitivity is extremely high. Using a test lead of two feet lenght as an antenna the regen hears everything on 40m that the R-388 can hear (which uses a 20 feet antenna). My shack is located under the roof in the second floor. But, the regen needs a good ground! In my installation this is a connection to the heating pipe. Of course, the selectivity is not comparable. But in most cases this is no problem (the selectivity is between the ears of the operator ;-)). Regeneration control is very smooth without any noticeable frequency pulling.

The big center knob is for band-spread tuning. The cap is a very simple device which I also found in my scrap box. I had to remove some of the rotor plates to get a tuning range from 7.0 to 7.1 MHz. This was very easy because of the simple construction. The advantage of this cap is that it rotates very smoothly. I don't use any reduction drive but tuning in an SSB station is no problem at all. In the lower left you see the control for the band-set capacitor. You will not find this cap in the bottom view photo below. This was an older version, where I wanted to use a ceramic switch for band changing. The knob in the lower right is for regeneration control.

The PS for my regen is mounted inside the box of a butchered PC supply. I ripped off everything and just kept the case, the AC input socket and the on-off switch. Two 330µF capacitors were also reused. It delivers about 70 Volts B+. In spite of the simple circuit, the voltage is quite stable and clean because the receiver draws very little current (abt 4 mA). Stabilization of the heater voltage was necessary to reduce the hum.

The plug in coil is tailored for the 40 meter band where we find a lot of active CW stations here in Germany. It has 17 turns (abt 9 µH) with the tap at 4-1/2 turns. The next one will have a lower tap so that oscillation starts at a slightly higher plate voltage.

Here are some more pictures (click on them to increase the size):

My shack, right side	My shack, left side	Regen, top view	Regen, left side view	Details inside
Regen, 3/4 back view	Regeneration control	Band set capacitor	Power supply, top view	Power supply, side view

Now it needs a MOPA companion!

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