Thx; my buck just went to China for a good cause.

Yep, me too, thanks.

Larry

They finally arrived in the mail yesterday (22 days). Anybody else get theirs?

Larry

I got mine in 16 days.

I've received small electronic items from China and Hong Kong in as little as 8 days, so this seller isn't the speediest, but for a buck and free shipping I can't complain too loud.

Hi all

Many thanks to the folks responsible for this little circuit. I have just completed a build using a little piece of perf board. I am new to laying out a schematic on a board and wonder if my inexperience is causing me bother.

Can anyone please post a layout for me? My set works somewhat but i wonder if my layout is responsible for two faults I have;
- almost any gain applied results in a distorted signal being received (should the 10k pot be log or lin? does it matter)
- no amount of fiddling with the trimmer cap changes the brightness of a small led. (I have tried a plastic 6-50pf and a ceramic 9-100pf)

Because of my location, I bought all parts from asia. Sometimes this is a crapshoot. Would a cheap lm386 or crystal osc cause my problems?

Many thanks to all the folks here again. I am just a beginner in the hobby and don't really have much in the way of value to contribute; but I sure appreciate the volume of knowledge here.

Kind regards
Paul WIllmott-Dalton

Sorry you are having issues, unfortunately I just realized the posted schematic on page one of this thread is missing a cap...

Check out this link, C2 is very important in reducing tendency to squeal due to RF entering the LM386 audio IC...

http://antiqueradios.com/gallery/main.p ... ewsIndex=1


As for layout, the antenna components(everything connected to pin #8 of IC2), should be placed as far from the audio input as possible...



Tom

many thanks for your reply Tom. I will try that.

Kind regards
Paul

http://www.ebay.com/itm/400292172818?_t ... EBIDX%3AIT

Looks like a work-around for finding alternate crystal frequencies...for under $10 its worth a try.
Dale

Dunno about now days but a few years back were so unstable weren't usable, can't modulate those either...

If stable would be fine for a 6888, 6GY6, etc xmittr...

Another possibility is the programmable oscillators from Digikey. You tell them the frequency and they program it.

https://www.digikey.com/product-search/ ... ageSize=25

Colin

I wish I has seen these boards earlier! A while ago I attempted to build a transmitter that used the LTC1799 (search this forum for BTa7000 to see it). The chip is surface mount, which made it difficult for me to assemble, but the oscillator did work. I didn't test it for stability, as the rest of the transmitter was a failure. I still have it, so I could hook it up to a frequency counter and see what it does. As Tom points out, it wouldn't substitute for the crystal oscillator in the LM386 transmitter. You can see in the BTa7000 that there is an FET that is switched by the oscillator. It was pointed out to me that the transmitter probably wasn't Part 15 compliant, so I didn't pursue it further. The design originated from overseas.

Colin

Hello Colin.
I'm surprised to find out you couldn't get the BTa7000 to work. I did make it clear it was 400mW input power and probably NOT P15 compliant, but I thought if you started building it, you had that in mind.
And yes, you cannot modulate the LTC1799 using the power source. It is an RC oscillator and you'll probably get some type of mixed AM and FM at the same time.
There is a simple way of getting the BTa7000 to comply with FCC rules - lower the Vcc. I suppose maybe at 7-8V it will go down to 100mW input. This lowered voltage will not affect the oscillator, as it works on 5V, but the class D output stage will lose power. Just measure the current, flowing from the TBA820 to the final BEFORE the coil.
I wish you all merry Christmas and a very joyful new year!
Bill
LZ1SWE
P.S. 6 months ago I did a 10W unit, using similar topology, just more powerful devices and a DDS module. Worked really well! It uses a serial modulator. Although it's in Bulgarian, you can check out the pictures, they make it all very clear. http://www.sandacite.com/forum/index.php?topic=6059

Hello Bill,

I think that the TBA820s that I bought from China were fake. I built a circuit as an amplifier driving a loudspeaker, and still they got very hot. I might have another go at this if I can find another source for them. The oscillator itself worked very well. Also, my layout is probably not ideal, so a rebuild would probably be the best idea. Did you ever design a printed circuit for it?

Merry Christmas,

Colin

No, I never got around to it. I sold maybe 10-12 of these units and then in June 2015 my baby daughter was born. Of course building transmitters was out of the question, you might imagine. Anyway, by then most of my friends at sandacite.com forum learned how to build it themselves and several did. Since then I have received 2-3 requests, but aaaa I don't feel like spending the time and effort anymore. But I offer my assistance to everyone willing to try it.
I was never sure you got my last 2 messages back then. I made a mistake on the schematic, witch causes oscillations in the amplifier! There is a Zobel network on the output pin, 1R and 220nF. In the first schematic I posted the cap was 22nF! This is REALLY low for the zobel to function properly and the amplifier turns oscillator. I'm really sorry about that mistake, I edited all my posts and the schematic, but by then I thought you left the project behind. Check the BTa7000 post again for the corrected schematic.
And yes, your layout needs some work. I urge you to follow mine, it's tested many times and it works great. Get it to work @ 400mW first, monitor it on a scope and start lowering Vcc. It should work down to maybe 6.5V, the lower limit for the 78L05, but I'm not sure. Try it and see.
I get notified about PM's and this is the best way to reach me.
All the best!
Bill
LZ1SWE

If lower B+ is desired on the final, why not use a LM-317 to set that voltage with both it and the 7805 running off the B+ supply.

That way the voltage to the final could be taken lower if necessary for part 15 compliance.

Happy new year, everyone!
Sure, this will work just fine. Just be sure to use the complete 317 setup, with the reverse diodes and a bigger output cap, 100uF will do, bypassed with 1uF S.M. or Wima MKP type, etc.

Looks like I'm really late to this party. Like many others I'm looking to build a AM transmitter for testing the alignment of my radios. Very long thread here that seems to have taken some twists and turns along the way. Is there a Kit still available that I could buy off someone, or could someone point me to the latest and greatest parts list and schematic? Thanks!

Well welcome to the party!!

Bill Hamre stocks most of the parts for the LM386 Tx but I believe he's wintering somewhere out in the Atlantic and not due back to PA for a couple months...

Transformer can be a wall wart that outputs 9-15v(refer to schematic)... Just be sure it's not a SMPS type(common in last 10 years or so), give away on those is they are very light for their size... If you have breadboard experience and and of course parts, one of these can be tossed together in 15-20 minutes...

http://antiqueradios.com/gallery/main.p ... ewsIndex=1

BTW the transformer supply for the 12AV6/12CS6 version has dried up... Really the LM386 version works just as well, just doesn't glow...

Tom

I built this kit, and it works very well with a wall wart for power;
http://www.ebay.com/itm/1308kHz-Amplitu ... Swv0tVOdAQ
As long as 1310 Kc is an open channel in your area.

He also carries this one, if you're into toobs;
http://www.ebay.com/itm/DIY-6i1P-6AJ8-S ... Sw5dNWpNkt
The advantage seems to be that it is tunable over a 200 Kc portion of the BCB.

I started one this weekend. I`ve been wanting to try this for a while but did`nt have time, So, I caught a bug and had to stay inside and thought I would feel better if I did something other than sleep. Got it on a breadboard now about ready to test. I`ll probably be asking questions later.