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The radio is not AM/FM, it is AM "Standard Broadcast" and shortwave, formerly used for international broadcasts. You may want to check to see if the loop antenna (the square-ish symbol at the left center) is connected. You could also try attaching a 5- or 10-ft piece of any kind of wire to the "A" (antenna) terminal to see if you can get some AM stations. This radio has only one IF (intermediate frequency) stage and so will not be a good performer for long-distance AM or shortwave, but could get local stations.

It does not contain a phono preamp as such, but was designed for a crystal or ceramic phono cartridge. The phono input contains a shunt capacitor (C28) for approximate equalization, but not an equalized preamp that would be required for a magnetic phono cartridge. If you just remove C28, the .005 uf capacitor, the response should be fairly normal for a "line" input from a phone or iPod.

If you want a stereo input to this radio, you can replace the RCA-type phono "socket" with a 3.5 mm stereo jack like this. You should connect the "sleeve" terminal of the jack to chassis ground, as the original RCA jack had. You can probably do that mechanically with a thin washer. To combine the two stereo channels, use a separate 10K ohm 1/4-watt resistor from the "tip" and "sleeve" connections on the jack and connect the other end of both to the the point "P" on the radio-phono switch. Using the resistors will correctly sum the two stereo channels from the incoming signal.

Interestingly, the schematic shows resistor values in an unusual way. The "M" means thousands of ohms, normally specified as "K" for kilohms. The "MEG" means megohms, millions of ohms.

Hope this helps!

Oh right!! 3D printing. I had not thought of that.

I saw a youtube channel once This guy had a nice vintage radio with a chicken head knob. He made a silicone cast and then used black epoxy to make his own knob. The tools and amount of work and detail he had to do to make it look good. He had a slotted shaft so made a small spring clip inside the round hole he drilled though.

But. for 3d printing. What if you 3d printed a knob to fit on top of metal collar with a set screw already in it. Something like this https://www.amazon.com/Lovejoy-LSC-10-Shaft-Collar-Plated/dp/B007JOHR9W/ref=lp_16411961_1_2?s=industrial&ie=UTF8&qid=1570770594&sr=1-2

you would need some kind of epoxy or maybe just a good friction fit to make the 3D printed part stick over this collar. And drill a hole to get to the set screw maybe. Or if you can. attach the collar and friction fit the 3D printed part over it?

Three approaches I'd take:

1. Cut a mask out of adhesive backed vinyl on a knife cutter, then chemically etch or sandblast the positive.
   
   
2. Cut a mask out of chipboard or plywood on the laser cutter, and similar to above, sandblast the positive
   
   
3. Do a light (.003 inch) engrave using a CNC.
   
   If you scribe by hand, something like liquid frisket might work better than shellac or a bituminous material. Frisket can be painted to a fine resolution with a pure sable hair brush, which is what I do for watercolors (using a size zero for detail work)...never used it for etching, however.

Nice setup! The right workspace makes the hobby so much more enjoyable. I added this magnifying task light last year and it's become my favorite tool on my bench.

Which one of the Fostex kits are those bookshelf speakers? I've been thinking about getting a pair and I'm curious to know what you think of them.

This book is great, goes into all the theory you need. As for building tube amps, execution is what yields a good amplifier in the end. Actually designing an amplifier, especially anything beyond medium gain is more of an art rather than a science.

I'm currently using some amount of "all of the above" from the parent post which has, like your setup grown organically over the years.

I have a few of these as well which I filled with cut-down 24-pack soda trays. It was a bit of leg-work to trim and re-staple the boxes but it has served me well thus far.

I also have a pair of two-drawer file cabinets which support my workbench that I am criminally under-utilizing right now. Any Ideas there? (besides hanging files, that is).

1. It was this or this.
   
   
2. I will test this tonight. Are you referring to the audio output ground on the pi and the amp input ground? I know you asked for AC voltage, just checking to see if you saw this DC voltage measurement from the head-fi thread:
   VDC difference from pi output ground to amp input ground (NOTE: Amp and Pi are NOT connected at this point)
   453-463 mV DC
   
   
3. I will test this tonight.
   
   As far as item 1, if this is not a "good" 5 VDC regulator, I would be willing to buy a different one. The downside of my circuit design is now my wall wart is working all the time, and inefficiently at that. It gets fairly hot, although IIRC, it might do that even when just connected to the amp with it off. I suppose it is technically doing it's own 120VAC to 24VAC regulation all the time, so that would explain the heat without the amp running.
   
   Thanks for your help, I really appreciate it.

Helpful advice, thanks. If I have any joy, I'll post the results back here but it might take a long time. I may need to message you later, if thats ok as you seem to know what you're doing. I'll try to be concise and research my questions first. I noticed there are many different types of uno around, I assume I should get one with the right I/O to fit the chip I will use, as the Rev 3 has a chip slot (not sure of technical name) with 28 pins, and as for the NTE74141 I have no idea how to connect it to the uno. Speaking of chips, can you please explain a bit more which chip I should use, since they are very differently priced and I am a bit lost, sorry for the bother.

Haha, thanks! Just a roll of white photo backdrop paper and a photo strobe with a 22" beauty dish and sock.

You mean these?

http://imgur.com/gallery/Jmu5C

Those are some binding/terminal blocks I made awhile back for testing speakers/drivers, etc. I can plug in cables with banana plugs on them, and clip on to the terminals to test different drivers, etc.

There's some led tape/strip lighting under the top most shelf, and a clamp on adjustable led light with magnifying glass built in. I can swing it in when I need, and out of the way otherwise.

I think the magnifying lamp is this one: https://amzn.com/B00UW2IRJ2

The diagonal flush cutters are:
https://amzn.com/B000IBSFAI

and the small nose pliers are:
https://amzn.com/B0006N73BU

The little parts boxes are from a Bosch organizer:
https://amzn.com/B00BD5G6X6

There's cheaper options, but I had the organizer and extra bins so I used those.

Fire extinguisher is a Kidde ~3lb standard fire extinguisher. An absolute must imo.

The drawers are great, when I'm properly using them I can keep the desk clutter free.

Generally when I'm working on a project, if it's going to take longer than an hour or so, I put all the parts needed into bins, organize/label all the components. Then get started on the build. I have a small whiteboard to the left of the desk that I can pin up schematics, and take any quick notes while I'm cussing myself for forgetting something obvious.

You're correct, it is 12vac. I think this should work, I luckily had one in the parts bin: https://www.amazon.com/dp/B009B1IVW8/ref=cm_sw_r_cp_apa_i_cpE8AbX1G10BN

I plan on trying to make a little guitar amp with it. I found someone else that fed the left output into the right input in order to make a 2 stage single channel preamp. I just ordered a little solid state amp for the power stage, I'll try and post on here how it goes. I did solder in a 3.5mm jack so that I could use an aux cord, as I have nothing that uses rca besides a vcr!

One thing I did wrong and I'd suggest you do, is make sure you get one that can handle higher amps. Some tube amps do pull upwards of 5 or 6 amps, and I got a 3 amp one and have burned a fuse or two with that being setup incorrectly, once I figured that out, I was careful to not over do it, but it was only one amp that ran at about 4A I think, not sure I recall the model etc, and it's only been one amp, but that's one important thing to consider. If you're going to use it a lot, it's worth saving up and getting a well built brand, but if not, then go for the cheaper models. I think I got this one: https://smile.amazon.com/Parts-Express-Variac-Variable-Transformer/dp/B00BXJYO6I/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1519332865&sr=1-1-catcorr&keywords=variac but it's the 3A version, here's one that's 5A and less expensive, but not sure how great it would be: https://smile.amazon.com/dp/B076Y2XHRS/ref=sspa_dk_detail_3?psc=1&pd_rd_i=B076Y2XHRS&pd_rd_wg=aRA3q&pd_rd_r=CS27F03X270JC48FRH4E&pd_rd_w=YJVX3

If I were to do it again, I'd likely go for one like this that's also an isolation transformer: https://smile.amazon.com/Variac-Variable-Transformer-Isolation-1000va/dp/B006NGC6HU/ref=sr_1_1?s=electronics&ie=UTF8&qid=1519332960&sr=1-1&keywords=variable+isolation+transformer