All, I've got lots of old AM radios scattered around the house and I'm thinking I'll build a low power AM transmitter so I can broadcast FM, ipod, CD's etc through the transmitter so it can be played by my AM radio's. I've seen plans on the internet but I'd like to build one that has decent audio quality. I only need to have a hundred feet or so of range. I've repaired lots of radios and test gear but I've never built anything before so any tips would greatly be appreciated. The Li'I 7 looks interesting http://antiqueradio.org/transmitter.htm and simple to build but I'm not sure what to expect for audio quality. I'd prefer to build something with tubes. Has anyone ever built the Li'I 7? Anyone have plans for a transmitter that has good audio quality?
Thanks,
Keith

That's not a good unit to build compared to others that are of more recent design.

The Homebrew section has many schematics for nice little transmitters that have already been built by the dozens. The ones using a 6888 or 6GY6 plus an additional tube or two work really well.

I'm sure that within a few minutes you will have links to the other discussions posted in reply to your inquiry.

Thanks Dennis, I've never noticed that they was a homebrew forum. I'll try seaching the archives.
Keith

I have one transmitter that I built and have plans and schematic if interested not hard to build if you have a lot of parts laying around can email them to you

Daniel, are you pleased with the audio quality?
Keith

I also have a harder to build plan and schematic for a AM transmitter that uses more tubes

http://antiqueradios.com/forums/viewtop ... =6888+6gy6

I've been using the 12AU7/6GY6 version for over four years, it runs almost 24/7 and I'd est it has well over 15K hours at this point(made a post about it earlier this year)...

I haven't found Norm's original 6888 schematic, search is nearly useless her on ARF as nothing is found before the last software upgrade...

Edit

Here you go, I sidestepped ARF's crap software and posted Norm's original design on my web space... If you don't have the 6888 tube it was also built using a 6LE8 that performs nicely... Also Bob Weaver recently posted a schematic on a one tube 6CQ8 Tx, It's just a bit lower here in Homebrew...

http://members.cox.net/35z5/norm6888ps.jpg


tom

I got the transmitter kit that AES offers for Christmas several years ago. Only one tube, but it works OK.

http://www.electronixandmore.com/project/10.html

Above is a link to Norm Leal's 6AB4 & 6888 two tube AM transmitter. Refer to version 2 of the schematic. Yes, the audio quality of this one is exceptional.

Thanks for posting

If you should elect to build the 6AB4-6888 transmitter, you will want to purchase the Hammond 262E6 power transformer (not the Hammond 262D6 that was mentioned in the description) if you choose the alternate power supply version. The transformer is somewhat pricey (around $36.00 through Mouser Electronics), but at least it's made in the USA.

This is the AES unit. Here is the description from their website; cost is $39.95 plus s&h:

Sorry but the dual control units(6888, 6GY6, etc) we've built here on ARF, are in a different league than that phono osc, ancient pentagrid converters(6/12SA7, 6/12BE6 etc)will only modulate maybe 35% before distortion becomes a issue... The dual control tubes will modulate 95%+ cleanly...


Tom

fun to build these small projects , I just wanted a new style to build , have plenty transformers , probley will use another power supply box from a computor , unless can find a nother small radio chassis , seems I might have one more old emerson chassis could use

I guess each to their own. I got mine for Christmas (along with CD recordings of some old-time radio shows) a few years back, so the price was right, plus I enjoyed building it. Under what conditions do you get distortion? I haven't had that problem, but then again the only radio I have ever played it through is my 1936 Air King 21 - which is about as far from a hi-fi set as you can get (cheap, Depression-era TRF mini/kitchen radio).

Start with something simple like this:


Cost was just scrounging a bit. No antenna or ground. The ferrite rod couples to radios a meter or so just fine. Sound is good. The parts can be reused for a tube 6LE8 or 6888 for more range. Eventually I'll stuff it in a smaller box but now it's modular so I can use the parts for other things.

Doug

I have a screen modulated unit in development that uses three triodes and a beam power or power pentode for output... The idea was to build a mid/late 30s unit that uses all ST tubes... Lineup consists of a 6J5G, 6F8G(or two additional 6J5G) 6V6G or 6L6G and a 80 or 5Y3G rectifer, I'll post the schematic if you are interested...


Tom

We're interested.

I think that the next transmitter should include a tube rectifier (such as the one that you are making up).

More Than interested