Hi All.I hope this is the right forum for this .Mods can move it to the right forum. Ok I have here a Lafayette two tube am radio transmitter.It still works.I tryed looking everywhere on the net for info.but coming up with zero info.Photos below.Tubes are 12BE6 and 35W4.Made in Japan.The caps look like probably the mid to late 1960's.

Top Front



Bottom



Back with audio input.




By looking at it .I don't know if this was a kit or pre-made.There is no model numbers on the rig.It looks like it came off.

Since the sockets are secured with screws it's probably a kit, no doubt a version of the 30s phono osc that are prone to FMing & weak modulation due to the remote cutoff 12BE6 used... It's far from a stellar piece of equipment...

Since it has no power transformer it's potentially dangerous, if you plan on using it it should be recaped and verified the input is isolated via a cap from the AC line...

Tom

I had one of those when I was a kid...never could get any range out of it but I could get an occasional shock...cheers..Alan

I had an even uglier Lafayette like that in the early 1960's, every connection was exposed, and the top-mounted ballast resistor got hotter than the tubes. Terrible performance.
Don

I see that your 35W4 is the one with the Jane Russell plates, sought after by tube audio aficionados for its sultry sound. You may want to advertise it on eBay.

Thanks guys.Yes its performance stinks on range in the same boat as the Ramsey AM1 transmitter.My cordless phones have better range then this transmitter.I think I got it at the fleamarket for a couple of dollars years ago.

I found this Youtube video from hamradio nation com.

http://www.youtube.com/watch?v=Mk9r5m-e ... r_embedded


Yes Bob The 35W4 .Isn't she cute.Thanks for the tip.

I know I am going to regret asking this, but what are "Jane Russel" plates?

Dave

It's the hourglass figure.

Boy am I dumb! Thanks. I thought it would probably make me feel stupid.

Dave

I have another AM tube transmitter boxed somewere.Its a light blue and its a babysitter type transmitter.I can't recall the brand .I'll post if it shows up .I do recall it had better coverage then this Lafayette has.

Attach a full wave, long wire antennea to - I bet it'll sing...

If nothin' else, it'll hum...

Tom

I couldn't find anything more than some textual references but that thing is a 7-pin version of the ubiquitous "wireless phonograph" that was popular in the 1930's and 1940's. The idea was you could listen to a 'record player' through your spiffy console radio, if it didn't already have a phono input, using its audio power amplifier and speaker rather than duplicating that cost in a standalone 'record player'.

Here is the Zenith version The 12BE6 and 35W4 are 7-pin equivalents to the 12SA7 and 35Z4. The honker resistor you see underneath substitutes for the "ballast tube" to bring the series filament string up to 120V. Note, there's more dissipated in the 'ballast' resistor than the heaters themselves.

Component values are not necessarily identical but the basic circuit is the same.

You can see the safety issue. If C5 shorts you've potentially got live AC on the 'ground' (and chassis). That may not be quite as bad if going to an 'insulated' ceramic cartridge inside a 'record player' but if that's going to a ground referenced device there's going to be lots of fireworks. Or, if the other device is isolated then your hand is the 'ground connection’ The same applies to the chassis.

There's no good way to fix that without a power transformer isolating the circuit from AC and here is the AES 'modern' version of the exact same thing. The 12SA7/12BE6 is remote cutoff so modulation is limited to, say, 50%, above which serious distortion sets in. A better choice would be the sharp cutoff "Dual Control Heptode" 12CS6 but it would take different component values. Range would be improved with an antenna matching network.

FWIW,

I had this AES rig years ago and liked the audio. The transmit distance wasn't that great though. Your mileage may vary.

K

Well, I was being a bit conservative. Nachbaur claimed 80% mod after 'culling' for the best 12BE6 he had, but doesn't specify just how much distortion there is at his 'specially selected' 80%, and the 'typical' G3 curves visually indicate 50-60% is the extent of the 'linear region'.

Having said that, reduced modulation (to stay in the linear region) shows up as lower volume, but there's a volume knob on the radio, and a higher noise floor, since the 'peak' volume is lower. However, 'music' is dynamic with the average program level 10 dB (customary spec) lower than transient peaks so if you increase mod depth for the 'average loudness' it's the transient peaks which are distorted. Now, that's not 'terrific' but I think it's primarily 2nd harmonic distortion so it may not 'sound' as bad as a straight reading of the curves suggests.

The 'more linear' 12CS6 won't do 'full linear' 100% mod either so the difference between the two is maybe 4 dB, which is noticeable but not a huge difference.

Human perception is amazingly resilient and adaptive, and while there are many examples I think my sister holds the record. She swears to have watched 'color TV' at a time not only before we had one but on shows that were filmed in B&W so they couldn't possibly have been in color even if we did. Her mind simply knew what the colors 'should be' and subconsciously filled them in. Voilà, 'color TV'.

I mean, it's tough to imagine a 'signal' more distorted than not even being there

Hi

This circuit uses a modulated oscillator. Modulating an oscillator causes shift in transmitter frequency, FM. It's heard as distortion except when using a crystal controlled osc. Believe 50% modulation is on the high side for this 12BE6 circuit.

The modulated osc xmitters have a double whammy against them, but likely the remote cutoff *SA7/*BE6 is more of a issue than it being a modulated osc, most of the time those won't go much past 35% without distortion... Switching to a sharp cutoff 12CS6 would gain modulation capability, but the modulated osc issue would rear it's ugly head... Probably need a bias tweak to be at it's best... When using a modern line source without a extra amp stage, I wouldn't expect more than 25-30% modulation at most...

At close range, 50% carrier modulation doesn't sound bad at all, it's when you are some distance from the Tx that it becomes apparent...

With a transformer and other components the chassis could be used for building one of the 6C4/6GY6 Tx that are so near & dear to my heart(ain't that a tear jerker?)... Still being open on the sides and bottom, additional shielding would be advisable... I've often though of rebuilding a Knight Broadcaster into a decent performing Tx, but mostly keep the one I have around as a nostalgia piece...

Tom

Thanks again on all the input guys.I notice on that video the filter cap on top is gone.I wonder if he installed one underneith the unit.I wish he would of provide more info on his site about this transmitter.I have mine setup like he did with the Ipod feeding it with a 4 ft long wire hookup.I should isolate the ipod with a input transformer to protect it from getting blown out from the high voltage if something goes wrong.I know I did not build this kit but who ever did . they did a nice solder and assembly job on it.Also I'll look around for other set of 12BE6's and 35W4's and see if theres an improvement with the xmitter.

Yeah, FMing can be a problem but, ya know, I don't think I've ever heard anyone explain what causes it. Do you have one? Miller capacitance?