If you don't have a old one around, pickup a earlyish P-IV or AMD Athlon/Sempron 'puter and load your music on to it(usually cheap on C'list).. Can use Windows Media player to make play lists that last for as long as the amount music you have, then repeat if you like... WMP-10(also ver-9 in XP) has the ability to level the audio so over/under modulation isn't a issue when playing a wide viariety of songs, plus 10(only) has a option to shuffle the play list prior to starting... Both versions have a shuffle on the fly option but seems with 100s of songs in a playlist, it will get fixated on playing the the same 40 or so over and over... I really dunno if ver 10 has this problem(9 surely does), I just shuffle the list a couple times when I start and let her rip... Most that use WMP agree versions 11 & above suck... They are OK if all your music is on commercial CD, but with individual Mp3 files it's cumbersome to use...

Tom

When I use my two tube 6GY6 broadcaster I play WRDV from my computer to my transmitter. They play a wide variety of the older music.

Tom & Tube Radio: Thanks guys for the info. Yes, that's certainly advantageous as opposed to the CD player. With the current set up, the Califone boom box CD player will play (at random) a CD containing 21 old 1930's songs. It will do this for about 90 minutes, and then it will stop. I will then have to run upstairs and press the "Play" button again---and the cycle will repeat.

I don't seem to have a problem however with over/under modulation when transmitting any CD songs from the boom box to the dining room downstairs----I just set the boom box volume level to midpoint, and that's all there is to do. The sound quality with the 12AV6-12CS6 transmitter is simply superb. There's no noise, hiss, static, squeals, hums----just pure nostalgic '30's music.

I don't have much problem with over modulation either. I built a VU meter in mine set to where the needle just reads in the red when I just do begin to over modulate. I do know some radios namely the ones without AVC do not like much modulation if their antenna is near the transmitter's antenna. Also some pocket transistor radios don't agree with much modulation either.

I drive my transmitter with one of the AUX send outputs on my Yamaha 20 channel mixer. That way I can send any source to the transmitter without moving cables around and have a way to adjust the tone if need be.

Over/under modulation only seems to be a issue with some of my MP3 files, I have a few that vary in amplitude... I recently run every thing I have through a program called Mp3 Gain and now mostly isn't a issue...

Tom

I actually run my transmitter input through a stereo compressor which I have set to compress most music pretty heavily, with a slightly delayed attack time, and the longest release time possible. I think I'm using a 3:1 ratio or so. Since my input varies from LPs to MP3s to whatever I'm watching on TV, that turned out to be a simpler solution. What I really need is some sort of AGC device, but I have to find another one on the cheap.

-Dan

I do notice that with my AK-40 radio given it is in the same room as the transmitter I have to either turn the audio gain down on the transmitter or de-tune the pi network to reduce the amount of signal so as not to overload the radio.

(newbie intro) Hi, my name's Sam and I want to ask a couple questions about the 12AV6-12CS6 transmitter.

I ordered and received the kit from Bill (thanks!) except for the transformer - he was out of them at the time.
So I'm just in the planning/parts gathering stage.
I have a strong station about five miles away, exactly on 1000khz - so I have to use the alternate frequency.
I've ordered and waiting on a 680 uH choke & 1228kc crystal osc, and have the perfboard.

First grouped question is around the antenna matching/tuning components...
The parts list calls for VC1 to be a 365pF cap (AA5) - I think this means rip it from a dead AA5 chassis?
And the coil L2 is to be 680uH for 1228khz version.
But... the photos posted don't jibe with this, there's a variable inductor and a trimmer cap used.
http://members.cox.net/35z3/12cs6txc.jpg
http://members.cox.net/35z3/12cs6txd.jpg

Would using a variable inductor give me better flexibility in matching up to various antennas (say for a temporary setup in a parking lot)?

If I wanted to include some kind of matching, output or SWR indicator... any ideas for something relatively simple, but with a little wow-factor for the kids?

Next subject - as I said, waiting on the transformer and the Gold Mine place is sold out, no specs or anything available online. So I don't know the footprint or the ratings. I'm thinking of 'embedding' an MP3 player into the same enclosure - something like this: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=320-350
This is an example, there are several on the market to choose from.

Question is, assuming I beefed-up the zener diode - does that transformer have enough capacity to handle another half amp at five volts? I don't want a hot potato in there.

Many thanks for lending your knowledge in these forums - I've learned a lot!

-Sam T.

Sam

Yes, Electronic Gold Mine is sold out but I ordered 100 transformers when we first decided on this circuit. I have been sending Bill 12 at a time and more are on the way.

The 24 volt winding on this transformer has plenty of extra current. You will need to drop 24 down to 5 volts with a regulator or resistor. Whatever you use will dissipate heat. Careful as ground on this power supply isn't one of the transformer leads.

Hi Sam

The variable inductor you mention is used in place of L1, is only used to block RF from feeding back into the power supply, the 1mh supplied in the kit works just as well... The var cap is something from the goodie chest, most adj type cap would be fine... The reason the pictured components are different is it's the prototype and not one that was built with the actual kit, it's parts were finalized sometime later....

SWR meter eh??? With the short antenna and Loooong wavelength, I don't know if SWR could even be measured... Would no doubt require a loading coil be added to the antenna...

The 5v is defiantly a no go, the circuit as is barely produces enough current to power the Xtal osc, which is approx 2ma(additional load on the B+ will increase this figure though)... If you wanted to tap from the 24v winding(blue & white wire junction) into a regulator circuit, I suppose it would be possible, transformer will defiantly handle the extra current... Depending on current draw the zener wattage and value of the electrolytic cap may need to be increased...

Edit

I see Norm slipped in while I was off yacking on the phone... The point about ground is certainly valid, cannot be the second transformer lead...

Tom

Thanks Norm and Tom for the clarifications.

Since I'll be using a bigger enclosure anyway, adding a second small power supply isn't a problem - I already have one constructed on a small board. For an enclosure, I'm thinking something like a cabinet from a dead boatanchor out of metal - but any old radio cabinet would do.

The indicator wouldn't necessarily need to be for SWR but I was hoping for some way to visually indicate the optimum adjustment of the output circuit capacitor. I'll look through some old ham transmitter schematics for ideas and maybe bring up some options here for discussion. Offhand I'd guess one would be looking for maximum current through L2?

-Sam T.

A 50-100ua meter connected through a detector diode and current limiting resistor can be used for antenna peaking... Can also use same with the diode and loop of wire to use for peaking, the 50ua is best here...

I generally use a scope clipped to the antenna insulation...

Tom

Thanks - I have all parts now except the transformer, anxious to get started.

"Thanks - I have all parts now except the transformer, anxious to get started."

Maybe some more of the Gold Mine transformers are on the way?

I'll get that xformer out the minate that I get it. Should be early next week thanks to Norm.

xformer shipped this AM.

The 12AV6-12CS6 transmitter that I built a few months ago is still running super. Yes, I'm still using (and using it now!) the Califone Boom Box CD player with it, and I broadcast with the pair several times a week. It's a joy listening to 1930's music that's being transmitted downstairs to the 1929 Atwater Kent Model 55C AM receiver that I have in the dining room.

I sometimes listen to the broadcasts with the 1951 Philco AM/FM/Phono receiver that I also have in the dining room, but it seems that the '29 Atwater Kent has better audio.

How far is your transmitter from your receiver, Blustar? Granted, I live in a pretty noisy area (apartment complex), and I built mine in a plastic box rather than a metal one, but my usable range is maybe a 30 or 40 foot radius, and I don't think it would work upstairs either. I only get good clean audio with a directional antenna (like the loop antenna on my Zenith TO). I've always wondered if a metal box would have made a different, or perhaps different design considerations.

-Dan

Pianoman: The 12AV6-12CS6 transmitter is upstairs in a storage area, and is broadcasting downstairs through a floor and a couple of walls to the dining room. It's about 37 feet from the transmitter upstairs to the '29 Atwater Kent & '51 Philco downstairs, and I have more than enough (undistorted) audio with the Atwater Kent & the '51 Philco. The audio is clear and crisp.

For the enclosure, I'm using a Hammond 1591XXEBK (that can be obtained through Mouser). I have used this particular box (It's a plastic box) because it has mounting posts for two perfboards, and it's made in the USA. I used one half for the P.S., and the other half for the oscillator circuitry.

As for the antennae, I orginally used a Radio Shack hobby antennae with it (for portability), but I subsequently connected the antennae (via alligator clip leads) to a 10 foot piece of Romex that I had left over from a wiring job. I just have the other end of the Romex folded over, and placed over a curtain rod upstairs.

Hi Dan

Have you peaked the output with the trimmer cap??? Makes a noticeable difference when correct...


Tom