Home AM Transmitter (again!)

[Username1]

Hey that looks like a cool project...... Can you post a schematic? with voltages you are getting ?

jr_tech has a point about matching the source and load.... look at this:

http://en.wikipedia.org/wiki/Impedance_matching

What you want is for the output device to "see" a speaker or earphone load, And for the next stage to see its natural input resistance, or "impedance"

The circuit you have, the output device will be very unhappy whenever the volume control gets turned down under 1000 ohms. (just because I have seen headsets in the range of 1K to 8 ohms) The input of the tube circuit would like to see around 50Kohms or more I would imagine....

I found the circuit, you should try to get it working with the volume control at mid point, so it don't cut the tube off....

Remember maximum power transfer will only be 50% not that you will need that......

[Winky Dink]

Jr,
Regarding the wiring of the 47K resistor (R1), I don't see what you see. One end is grounded; the other end goes to tube pin 4 and C5 (68pF). Here's an updated photo of my build and the original schematic:





(Note to all: This is a tried and true design. See the whole story at Phil's Old Radios. This will take you to the AM Transmitter article: http://antiqueradio.org/transmitter.htm
If I knew what I was doing I'd be tempted to improve on this design, but I need to stick with the original which others have built successfully.)

And here are the voltages I get:



This is as far as I got with the project two years ago. I looked at the old notes, and the voltages were basically the same as they are now. So, do these values or the wiring seem true to the schematic and the expected function of the device?

To Username1: Thanks for the link to the impedance-matching article. I have not yet read it, but I see its relevance and will get to it as soon as I can.

[jr_tech]

Thanks for posting the improved picture... In the old picture, it looked like the green wire under the resistor (R-1) was connected to the lugs at each end of R-1, this is a much better pix, and at first glance the wiring appears to be correct, but I will print it and study more closely.
Have you tried swapping the wires to #1 & #2 of the coil (or # 3 & #4, but not both windings) to get oscillation? Phase of the coil matters, and perhaps these coils are reversed?

jr