Are car radios now DSP receivers that is software only? I wonder if it is possible to receive AM with the tiny antennas on some of the modern cars. I would have thought that you need longer antennas to receive AM.

Yes, my bad. You're right it seems, it does have an FM / AM radio, if this picture is correct. I guess he'd better not touch the screws then ...?

I wonder if you could try a search for the player model and add the word 'manual' or 'service manual' or something like that? But maybe you've already tried that.

Interesting project! I tried a DIY loop antenna last summer. I didn't get it to work as well as I had hoped ... I know, its been some months since you posted your project. But I'm curious, do you have any experiencies to share, good or bad, regarding your loop antenna and the loop amplifier circuit? As the spring progresses I might want to give my own loop project another go. Would you recomend the amplifier circuit that you use? And - does it work on the short wave bands?

I'll throw in my two cents as well ... I believe C4 will charge up to peak voltage from your 120V transformer, that will be around 170V. (square root of 2 multiplied by 120V) R4 is 2000 ohm, so even if you should short the 88V output to ground, the current will be at most 170/2000 = 84mA. Then, the power dissipated in R4 will be 14,5W Ofcourse, you will not short your voltage supply, so R4 rated at 10W will probably be just fine. It only needs to dissipate 3,2W normally (2000 multiplied by idle current squared). If you draw 40mA from your 88V output, the voltage drop in R4 will be 90V. At this point the regulator will no longer regulate. If the output current is increased beyond 40mA, the output voltage will start to drop. R5 will ''steal'' some current from the 40mA available. So, it could be a larger value consistant with how many seconds is required for the power supply to be considered safe to touch. I'd say 10 seconds would be like 47k, 1W or 2W would do. (Or maybe two 100kohms, 1W in parallell to avoid single point of faliure) EDIT: (after a cup of coffee) Came to think of it ... Zener diodes generate noise, so it would probably make sense to add a HF ceramic capasitor to ground from each of the 22V, 44V, ... etc outputs.

Glad you found it helpful. Keep us posted about your progress. A picture would also be nice! Old radios..! Do they have wooden cabinets that looks reasonably good? That's nostalgia..!

It is a bit confusing, I know. The coil is usually kept constant, so for AM-band, the coil is 200uH while the variable capasitor is 50pF to 500pF, depending on how much of the plates are meshed, by turning the tuning knob. Edit: We know how to draw the dotted line because we know the capasitor range, from 50 to 500 pF. Then we also know that the AM band goes from 500kHz to 1600kHz. So we draw a line from 500pF to 500kHz on the frequency scale, and see where it intersects the inductance line, in our case at 200uH. Now we keep the line fixed at 200uH and draw the line to 50pF. It intersects the frequency line at 1600kHz. So - no computer, no calculator, just a ruler and a pencil. For LW (long wave), the coil needs to be 2200uH to cover 150kHz to around 400kHz. You need a switch to cange the coils while using the same variable capasitor. OR - you can have a coil which plugs into a socket. Coils and crystal radios is 'magic'!

There are formulas for doing that, and even online web pages that let you calculate L and C for resonant circuits. HOWEVER ... I have an old book with what is known as a nomogram to do the same with just a ruler. I use it all the time. Here is a scan of the nomogram, short explanation below: Assuming your capasitor goes from 50pF to 500pF. Follow the dotted line, from 500pF on the right, up to 200uH on the left hand side. The line crosses the frequency at approximately 500 kHz. The same thing goes for 50pF. It crosses the frequency line at about 1600kHz. So - 50pF to 500pF, together with 200uH, covers the AM band from 500kHz to 1600kHz. If you find this nomogram helpful, I can post a nomogram for designing coils too if you are interested.

Impressive work! The ECH81 brings back happy memories. Many many years ago, in the mid 70'ies, I built a short wave receiver with ECH81 and an EF89 in the IF, and ECL82 audio. Thinking about it, I realize I haven't improved much over the years. Still building simple receivers, only difference is that I've replaced the tubes with transistors. 🙄

Incredible! How this kit has survived all these years. You are probably right, the kit belongs in a museum. Great find!

Great explanation! I have only a vague (and probably wrong) understanding of how the wadly loop is functioning, only that it is a clever design to cancel out VFO drift.

Yeah, I see what you mean. Those loose women are bad ...! 😁 I'm 68 and spend a lot of my time in a small shed in the garden. Building simple radioes that I always wanted to try, but never got around to do before. NZ is quite a ways from other countries. I believe even Australia has long since closed their short wave broadcasts. That leaves China as the only country pretty much dominating the airwaves. Although, I sometimes can hear Radio Japan and Thailand on the 31m band here in Norway. Looking foreward to hear what your radio can pick up. BTW: You've got some really nice tall coil cans in your radio!

Sounds great and the selectivity is impressive. I think I saw a crystal filter in there. What frequency is that at? I thought I saw very rapid fading signals on the S-meter, the reception may not be the best. I'd like to hear what it sounds like when the conditions are more stable. The A index is at 12 now, which means a quite unsteady atmosphere I think.

Very nice work. Valves are magic!

Looks a bit pricy and maybe too advanced for my capabilities. I can't help drooling a bit over it though! I'm thinking about trying a 'wobbler' kind of circuit to help aligning circuits. I have built a ramp generator as shown in this video by W2AEW: (494) #110: Circuit Fun: Flexible Ramp Generator to create frequency sweeps using 555 timer and op amps - YouTube (https://www.youtube.com/watch?v=bVahBmsvirE) The circuit works well, but I still have to build an oscillator to go with it and figure out how to hook it up to my chinese ''fnirsi' tablet oscilloscope, if it is indeed possible at all.

Interesting test equipment! The visual frequency sweep must be really useful.

Thank you Larry for setting this up and giving the radio community a place to share projects and get new ideas and inspiration!

Have you tried to use a seperate battery to power the local oscillator stage? It might help determin if the frequency pulling is caused by varying load on the battery with varying IF gain ...? Just a thought ... I must say; you have done an impressive amount of systematic work with this radio! Well done! I like the cross coupled oscillator. I think I will give it a try next.

The box looks really nice. I guess the aluminium chassis fits inside the outer wood box? There were aluminium boxes like that for sale some decades ago, but I have not seen anything like it adertised for years. Very pretty box. But I guess it depends on the price point. I guess still it will be cheaper that purchasing a 3D printer!

Hello to you all radio enthusiasts out there! I enjoyed lurking in the old radio board forum. coildog