I was not going to do this, but Gary (VALK) suggested it - here is a separate thread on my Transmitter build. All the posts in the "Post Something Random" thread have been moved here and are the first seven posts in this thread.


My latest obsession. I needed something to do in the severe cold winter of north Texas (where the temperature is often below 55F in the winter).

So Im going to get back on shortwave ham radio. Bought a basket-case HR1680 receiver, all that was wrong with it was a 2uF capacitor in the audio board.
Here it is, perking along, 45 years after some guy built it as a kit, detecting a signal from my generator at .3 millionths of a volt. Pretty good for an eBay "sold as-is, no returns" bargain.




Now to build the transmitter... My own design, made largely from genuine new-old-stock and junk parts. This will be 1960's tube-type technology, like what I used as a teen ager.

The design of the mod driver, AM modulator, RF driver and final PA is not done - but here's what I have so far. Once I get all this going, I will proceed with the second half of the project.

 

Construction has started..............
Building a VFO that is stable is too much to take on, I cheated, bought a Heath VFO, just like the one I had in junior high school, it needed only a cleaning of the band switch, here it is, powered by the power supply in the under-construction transmitter. Very stable.








The rear panel is done, just getting started...

 

Lots of cords and carpet ........BE CAREFUL

 

Santa is gonna bring you a lump of coal for that one!

 

Very impressive!

 

I ordered from Mouser, Tube Depot and RF Parts Company on Wednesday. I had three boxes on the porch by noon.

 

Talk about "old school"! Does Guglielmo Marconi know that you "borrowed" some of his parts?

 

One thing that is important is frequency stability - I did not want to even try to build a stable, easy to tune VFO (variable frequency oscillator) so I bought a 50 year old Heathkit VFO, bypassed some noisy switch contacts (that switch things I do not need to switch) and it works just fine. I had one of these when I was 14. This will serve as the "tuner" for the transmitter.





VFO Internals, that reduction drive is IMPOSSIBLE to find today - like looking for a genuine, working cupholder.

 

55 deg in the winter? Our igloos are warmer than that.

 

The balanced modulator works! I took the design from a 1960s transmitter because the carrier crystals and sideband filter I got off eBay came from one of them. But I could not get all the parts so I had to alter the design a bit. Today, my little toroid cores and enameled wire came in and I wound a toroidal transformer and added it to the board.

I got 42dB carrier suppression, spec was anything over 35dB is good enough. This was the most intimidating part of the build. I have more challenges, but this scared me most of all as I simply could not get the original RF transformer nor could I find any specs on it. The math seemed to imply that two windings of 44 turns of #26 enameled wire on a T50-2 core would work, and it did. (The schematic is of an SB-400 and the yellow box is the original balanced modulator.)

 

In 1975 I worked for a bank doing loans and mortgages. Made $9000 Canadian and spent $100 on a cutting edge pocket calculator. Not many features. Not solar or battery power. Had to be plugged in to work.

Don't even mention my old alarm clocks with the flip over numbers.
Or my old 24 inch big thick boat anchor of a TV before we went flat screen.

Starting to understand why some say the digital micro chips were so important in advancing technology.

I don't pretend to understand a great portion of your builds but find it very informative and interesting. I am learning though.

I started as a paramedic in 1979 and was amazed how our communications improved over the years. Just the addition of portable radios with repeaters to the trucks to talk to our dispatch was game changing.

Always amazed to find out how much I don't know but worse is realizing how much I don't know about what I don't know.

Thanks for sharing all this with us.

Jim

 

I started as a two-way or LMR radio technician in 1982 and worked as one up till about 1995, from then forward to 2011, I filled other technical roles including technician in the industry. From 2011 to now, I've primarily been with Kenwood COrporate or EFJohnson corporate, so 39 years in radio now. I know well of the advances you speak of over that time frame. When I started, I carried a TUBE CADDY around with me, altho most tube radios were gone by 1985 or so.

I also worked on the IMTS mobile phones of the day, the precursor to analog cell phones which were the precursor to the digital phones of today. From the age of 12, I knew what I wanted to do for a living and have spent a lifetime doing it.

I was not going to make a thread for this, Gary suggested it. I'm happy to see that at least one person is getting entertainment from it. This will probably be a LONG term project, had I gone solid state, it would have ben easier, but I wanted to do something different, remembering my first tube type equipment as a ham operator at age 14 in the 70's. Some parts are very hard to source and, frankly, Ive had to go back to 50 year old textbooks to refresh myself on tube basics. One other thing that slows me down, is with 300 volts buzzing around in the cabinet, one must be a LOT more careful than if this was a solid state, 12 volt project.

 

There was an episode of Jay Leno's Garage where he talked about where the future of car restoration was going.
It featured a Duesenberg that was 80 years old that a guy was restoring back to mint in his home garage. Parts that he could not find, he was able to fabricate in his garage. Jay commented good luck trying to restore any modern car 80 years from now. Electronics would be impossible.
Part of the reason I heeded the forum advice to have an extra RCM, camshaft sensor, and crankshaft sensor.

Ambulances here in the 1980s were Motorola radios. We got to know the tech very well as he was there at least once every 2 weeks to repair a truck.

Going further back I remember my dad testing tubes at a local store for our TV when something went wrong.
Whenever he opened up that TV all I could think was what a mess and potential disaster zone.

Been to quite a few electrical "incidents' over the years. I have a healthy respect for that stuff.
Be careful with your hobby, but you already know that.

Thanks again
Jim

 

I suggested it to be a thread where all the info about the build could be maintained.
I don't understand any of it but I read it entirely anyway.
Curious to see how many others here might understand this actually.

 

I don't understand all of it, but I recognize some of what you're using and why. After the Army I went to night courses at an electronics school in 1986. It was a course in computer electronics. Most of what I learned is obsolete now.
I've been following your build and I find it interesting and it brings back some memories.

 

As a kid in the 50s I was nailed several times when removing tubes from the TV for testing and replacing.

 

The build is evolving. That filter I designed the transmitter to use was a new-in-box dud. I found a 45 year old Heath original filter and just today I tested it in place, works like a CHAMP. Only about 3.5dB loss, spec is up to 4.8dB loss.

So, the design has changed a bit. I got the filter mounted and started building the post-filter mixer today. Cant find 2-56 hardware to mount the post-modulator amplifier tube so I guess I gotta order from Amazon. Even ACE hardware in Hurst does not carry anything that small.

Once I get all the below stuff working (in the diagram) I gotta build the mic amp/speech amp. Then align things and get it all working. THEN I will build the PA driver and PA stages. THEN, I build the AM modulator. Next will be to wire up a negative bias circuit for driver, final, post modulator amp, and cathode follower - to shut tubes down all the way while on standby, also, I will put an adjustable bias on the driver/final to switch them from class AB1 (SSB) to Class C (AM and CW). That will be part of the Push to talk/tx-rx switchover circuit. Again, that is easy stuff and comes last.

ANywya, things are progressing but I have a lot of work to do............... Editing the photos down to a good size is just too much work, since this is MY thread, Im not going to bother, but I hate how it looks.

 

Looking good!
Long gone are the days of strolling down to the local Radio Shack store to get what you needed. Like crystals for my scanner, a new mic or antenna for my car's citizen band radio.
You're rebuilding history sir!

 

Ok, gotta finish the mic amp and speech amp stages today. My 50 year old D104 mic, that I found on eBay for $35, came today. It is filthy, old, and the cable is crap but it does work if you bypass the cable.

I happened to have the Aeroflex here for the weekend, which is helpful, as it has an OUTSTANDING general purpose scope in it, in addition to the suite of RF test functions. Second photo is the D104 wired temporarily to the CH1 scope input. The mic cartridge is almost unmanageably sensitive on the '3920, it sounds good over the test channel, but it's a bit echo-y even at low setting. I think my transmitter will be way less sensitive so probably not going to be a problem, the 3920 is an outstanding instrument.

 

So, all three power supplies and the mic preamp/balanced modulator driver are done. After a good break, I will power it all up and test. The odd values of resistors (over 100k and even up to 10meg) is getting to be irritating. Im too impatient to order even more parts, so I made resistors with series and parallel combinations.