I'm not exactly sure why I pulled this old rig off the shelf, but I'll write up what I did -- I often use this blog as a kind of notebook. I can look back and easily see what I did on my last encounter with the rig.
The receiver is Doug DeMaw's Barebones (aka Barbados) Superhet. This was my first superhet receiver. I built in in 1997. The transmitter was my first real homebrew project -- it is the VXO 6 watter from QRP classics. I built it in the Dominican Republic, probably in 1993 or 1994. I built the power supply so that I could say that the entire rig is homebrew.
This rig is getting a bit long in the tooth: The receiver is built with 40673 Dual-Gate MOSFETs, an some of the transistor cans have gotten rusty. The frequency readout on the receiver is the top of a coffee can fitted onto the reduction drive behind the tuning knob from a Drake 2-B (not MY 2B!).
Here are two 2013 videos that I did on this receiver:
-- I put the crystal filter back in CW mode. I had widened it so that I could listen to 20 meter SSB, but I decided to go back to its original configuration. When I built the receiver in 1987, I didn't characterize the crystals -- I just used the capacitor values that Doug DeMaw had in his article. I pretty much did that again this time, just putting caps that are close in value to what Doug had. DeMaw used color burst crystals at 3.579 MHz. So I guess this would be a GREAT receiver for the Color Burst Liberation Army!
-- I used My Antuino (thanks Farhan!) to check the passband. Here is what it looks like. I just put the Antuino across the 10k resistors on either side of the input and output transformers. The coil cores had become very loose -- I just tried put them in the right place. I may need to put some wax in there to allow them to better stay in place. I think they could have used toroids instead -- that would have been easier. One of the transformer connections was open -- they don't work well that way, once I fixed that, the passband looks like this:
-- Each of the horizontal divisions is 500 Hz. The passband is not pretty, but it is OK, and I didn't feel like doing too much work on this to get it in better shape.
-- The filter peak was a bit lower in frequency than expected. I found that trimmer cap C3 in series with the BFO crystal would not allow me to lower its frequency sufficiently. So I moved C3 to a position in parallel with the crystal. With this mod, I could get the BFO frequency to 3578.69. This produces a 690 Hz tone when the received signal is at the peak of the IF passband. Opposite sideband rejection is quite good.
-- I didn't have to do any real work on the transmitter. The RF amplifier in the transmitter had served for a time as the RF amp in by 17 meter DSB rig (I had added a bias circuit, which I removed when I put the amplifier back in Class C). Some time ago I rebuilt the oscillator circuit (which had been literally cut off the board when I used the amplifier in the DSB rig).
-- I did have to reconfigure the muting circuit -- the T/R switch in the transmitter switches the antenna and also -- through a two wire circuit -- cuts off 12 V DC to the transmitter when in receive mode.
-- For sidetone I just put a small piezo buzzer through a 1k resistor between 12 V DC and the key line.
It all worked fine -- I talked to three stations on the high end of the 20 meter CW band.