Homebrew Receiver

Here is a 1950's nostiagia receiver I recently built.

It is a simple two tube superhet. The front end is a 6SB7Y pentagrid converter, which is followed by a half-lattice crystal filter made with WWII surplus crystals at about 455 khz. The crystal filter can be bypassed by replacing the crystals by an octal jumper plug. The filter is followed by a 6SN7 regenerative detector / audio amp combo. The audio amp is a cathode-follower which matches nicely to my roughly 300 ohm headphones.

The regen detector behaves very nicely, it does not pull easily, and handles strong SSB signals fine. It also sounds great on AM. I don't have any trouble spotting my transmitter -- with the receiver gain all the way down, and the regen all the way up, it doesn't pull or block. There is some interaction between the crystal filter and the regen detector. If the detector tank is tuned to exactly the frequency of one of the crystals, the detector will "plop" as it is tuned accross the crystal frequency. It isn't much of a problem in practice. The interaction also leads to some useful behaviour - by adjusting the regeneration control and the detector tank tuning, it is possible to obtain a situation that sounds like a Q-multiplier in action - A sharp peak in the response occurs that I think is centered on one of the filter crystals. The receiver has adequate gain for 80 meters, where I've been using it for CW. I am planning to make 40 and 20 meter coil sets, and I don't know if it will have enough gain for 20 meters. If it doesn't, I'll probably add a pentode IF amplifier.

The tuning capacitor is a very nice James Millen unit that has a worm drive and anti-backlash gear. It is very smooth, and has 50:1 reduction. The capacitor is coupled to a James Millen drum dial which provides rudimentary frequency indications. The resolution of the readout doesn't matter very much, as I use the receiver with a crystal controlled transmitter.

The IF transformer is salvaged from an old Philco AM radio.

Underneath is pretty simple. Some of the capacitors are not vintage units, I'll replace them eventually.

Here are details of the Millen drum dial. It matches up with the tuning capacitor very nicely.

I made coil sets for 40 and 20 meters. 40 meters was no problem, but the gain was a little low on 20. I was able to increase the overall gain by changing the audio output stage from a cathode follower to a conventional plate-loaded transformer circuit. This provides enough gain for 20 meters. On all bands a fraction of a microvolt is discernable. The front end does pull somewhat on 20 meters as the RF gain control is varied.

Here's a photo with the transformer in place, also, on octal plug with jumpers is visible in place of the crystals - this bypasses the filter.

Here are some rough schematics...

front end

crystal filter

detector and audio

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