02/03/2008 | AA4LR Last year, I operated with a two-tube crystal-controlled 40m transmitter that I had built over Christmas vacation. This year, I decided to build a companion receiver. What I didn't count on was that building a receiver is about five times more complicated than building a transmitter. The receiver wasn't quite finished before SKN, so I had to use my K2.

The receiver is loosely based on the NorCal Sierra. I decided that since the transmitter uses tubes, the receiver should use all integrated circuits. I built it backwards, starting with the audio stage - an LM386. Then the SA612A product detector. Next is the MC1350 IF amplifier. At this point, I had a lot of oscillation, which turned out to be a problem with the LM386. It took me about two days to figure this out. I then added the LM324 to form the AGC loop. I had then lost all sensitivity. Took me a while to figure out it was a solder blob across the input leads of the LM386! The IF chain uses 4.915 crystals, and appears to be extremely narrow -- great for CW.

I still have to add the SA612A mixer / oscillator stage, add another circuit for an S-meter amplifier, and mount the rig in a nice box that I have. Fabricating the dial for the 4:1 ratio variable cap should be interesting.

The transmitter saw a couple of improvements as well. I removed the old front panel that had a couple of extra holes and built a new front panel. I repositioned the meter to make the rig a bit more compact. I cut out a top cover from some perforated aluminum I bought about 15 years ago. I've enclosed a before and after picture. I also replaced the slightly soft 6146 with a NOS unit that develops the full 50 watts output.

Last year, I only used one crystal - 7075 kHz. I managed to buy a few more off eBay that were closer to the action. Unfortunately, this also meant there was a lot more QRM, but I made one contact each on 7038, 7042 and 7047 kHz.

I did have one bit of trouble trying to hook up my K2 to use as a receiver. Turned, I disconnected the wrong cable from my antenna switch and attached to the transmitter. I ended up putting about a dozen or two watts into the front end of the K2. It doesn't appear any worse for wear.

Only three contacts this year. next year, I'll have the receiver finished and try to put some more time in. -- AA4LR