Lowered AM into the AER

I lowered the AM signal to see how the set responded.

The blue is AM and the red is the audio on the transformer input. The AM is still quite high but the AF is much cleaner.

AF amp in a j-box

The little AF amp is so sensitive it tends to pick up noise and I had to tame the rascal. I built a new one on a handy box cover. For those not familiar with a handy box it is an electrical junction box. The box is about 2"x2"x4". (some are 1-1/2" deep)

I plan on keeping this one so I put a switch, volume control, RCA socket and earphone jack.

I do ugly construction. It's not pretty but it works well. I'm using the AF transformer to isolate the phone connections. It is basically a 1:1 a 1:6 would probably give a better Z match.

This is the j-box. the two screws in the cover screw into the box and my amp is shielded.

AER-1A SPICE sim package

The oscillator we intend to use.

In the final project we will use a DBM but for the sim I used this product detector because I had already "built" it in SPICE.

The AM signal.

The local oscillator signal.

The output from the Product Detector. It is distorting badly on the negative excursion.

The output from the AF amp. Yep! It is over driving. I could lower the AM signal and it would help. Looks like AGC maybe in order? You can download the SPICE model and play with it.

The AER-1A spice schematic

Be aware the model is very slow loading. You can adjust the time to get a quicker response. I'm showing 10 cycles of the AF and started displaying 50 ms into the run. I wanted to let it settle before displaying.

Inductors for the AER-1

 Fair Radio is selling these 2 pounds for $10. The board is 4" X 6". I'm testing according to the attached article.

k669 amp another build

 In the previous version I used 220mh chokes. I have some on hand so why not? This is not a common junk box item so I did another with some readily available 4.7mh chokes. While I was at it I made a smaller board for the build. I used this one without the output transformer. It has a reasonably good output. The one with the transformer produces an output with the AF generator control on minimum. This one requires the adjustment to be set a little off the bottom. I think I can add a transformer and it will compete with the first one. That will be another day.

I wanted to try a build that anyone could do without having to hunt the parts. This one works great with the 2SK669s and does a good job with the BSS123. I think it would work with a little tweaking with 2N7002 which is another common component.
EDIT:
I made this one with pins which are just stuck in the board. If you solder sockets to the pins heads you can simply plug in different MOSFETs and see which ones work.
You could not use chokes and it will work fairly well. The chokes do give a little boost on the output.
Use what you have and have fun experimenting!

Put an output transformer on the 2SK669 amp

I decided this one is a keeper so I installed a phone jack and an output transformer.
The observant one will notice the transformer has a plug attached to it. This was a 9 volt wall wart before it became my output transformer. I connected it to my DBM and signal generator. I picked up several signals from 3 to 10 mhz.

tested the 2SK669 circuit

I built this one last night. I hooked my AF generator to it with the output at minimum. I could hear the tone. I put my meter across the input and it was to low to read. When I adjusted the input to 10uv (the first digit on my meter) it was loud enough.
As I was connecting the leads I could hear some buzzing. I put my scope on C2 and when I hooked a lead wire to the input I got about 3 volts pk-pk at 1.7 mhz. The little amp is so strong I will need to filter and/or shield it.