PW Single Tube AM Transmitter

[ka1tdq]

I'm almost finished with this 3 watt plate modulated 5763 tube.  Grid drive comes from a project in June's issue of CQ magazine.  It take a low power VFO input and converts the output for a higher impedance. 

I'm using Heising modulation of the B+ and using a low power solid state audio amplifier for the audio drive. 

The small box connected to the big box is just an on/off relay to remove the VFO drive from the grid driver during receive periods. 

It looks good on paper!  The damn thing should work when I get it done.

Jon
KA1TDQ

[W2PFY]

I was thinking the other day that  it's about time for another installment from you What are you going to do with it?

The last time you had something on here it was about a 4-65 transmitter but I didn't see any follow up on it. Today I noticed a video on YouTube. Glad you got err done!!

Who makes the cross needle swr meters that you are using?

Have fun and it looks great and not cluttered.

[ka1tdq]

Yeah, the 4-65A transmitter works great!  With a dipole (at my old QTH) and my pair of 3-500's, I was a big boy signal too.  I'm renting right now and looking to buy a home so I can't really get on the air... antenna issues and my amp isn't hooked up.  But soon I'll be burning a hole in the atmosphere!

Daiwa makes the wattmeters.

This project came about from the working pieces of other (failed) projects.  I was trying to think of how I could plug them all together and came up with this.  I'm not really sure what to do with it.  Mobile?  With a small linear?  It might just sit in my office at work as a novelty piece... sorta of a 'whatisit'?

Jon
KA1TDQ

[W4AAB]

I would love to see a schematic. Looks good!!

[ka1tdq]

Here is the schematic.  I used boxes for simplicity for the grid drive.  The project from the CQ article does work.  Using 13.8 vdc I saw a 40 volt swing (unloaded) on the scope coming from the output of the box. 

Jon
KA1TDQ

[The Slab Bacon]

50K cathode resistor?? Or is that for a "low power tune-up" mode?

An interesting thought might be to stick one of those 5W TO-220 audio amp ICs under the chassis for the modder and eliminate the external audio amp. Just run it on the rectified filament supply.

[ka1tdq]

The 50K is for receive periods to eliminate the the cathode going to a million volts.  I guess it's a little easier on the tube... after all, it's only a little 5763.  Must be nice to it. 

If it works I might just put a little solid state audio amp in there just to make it a complete package.