25 Watts From a Single IRF510

I should have tried this a long time ago.  It works great.  The power supply that I picked up at the Kempton Park rally many years ago  happens to have a 25 volt unregulated output.  Coincidence you say?  I think not.  TRGHS.  

 Farhan provides a really excellent description of how to do this:

http://hfsignals.blogspot.com/p/25-watt-linear-for-40-and-20.html

"Sideband Suzy" and the History of SSB

Farhan alerted us to a very interesting presentation on the history of single sideband:  It was in episode 81 of Bob Heil's "Ham Nation" show.  It starts at minute 22:

https://www.youtube.com/watch?v=xSF0WBdK1IQ&feature=youtu.be

Two things really caught my attention:

-- Note how OM Carson, way back in 1915, had figured out how to get rid of the carrier, but needed some way of eliminating the unnecessary sideband.  He did it by using his antenna tuner as a filter.  FB OM!

-- In the early days of SSB, when it was an exciting new technology, hams had regular "sideband dinners."  At these events an award was presented.  Kind of like an Oscar or an Emmy I guess.   The award was the "Sideband Suzy" (see above).    Kind of a classic figure...  but half of Suzy was missing!

Putting a Heatsink on the BITX40 Module

The fan that I installed yesterday was driving me nuts.  It was noisy, both acoustically and electrically.  And I would occasionally get my fingers in the blades.  Not good.  While it did seem to keep the IRF510 from getting too hot, I knew that a real heatsink would do better thermally.

But how was I going to attach the sink to the transistor?  That tab on the IRF510 goes to the collector, so if it touches a grounded heat sink, you get a short.   A nylon screw and some mylar between the transistor tab and the heat sink is one option.  But I didn't have a nylon screw.  So I decided to just keep the heat sink electrically insulated from the chassis.

This project required me to refresh my memory on how to tap a 4-40 hole.  I went back and watched the short video I made on the tribal knowledge that Pete had shared with me.  Out came the Tap and Die gear and the machine oil.  The process went very smoothly.

Here is what I did to get the heatsink in place:

1) After removing the original heatsink, I gently bent the leads on the IRF510 so that the transistors outer edge would be flush with the edge of the PC board.
2) I put a strip of thick tape (Gorilla Tape) along the lower side of the heat sink. This will keep the heat sink from shorting to the chassis.
3) I placed the heatsink where I wanted it, and carefully marked where the mounting screw (through the transistor's tab) should go.
4) Drill!  Tap!  (see video)  https://www.youtube.com/watch?v=LuqliWT1k5A
5) I applied some heat sink compound (or Desitin!) and then attached the transistor to the heatsink.
6) I put a few drops of glue between the heatsink and the board and the chassis, just to mechanically stabilize it a bit.
7) Bob's your uncle.

It seems to work great.  The MOSFET stays cool. even after long "old buzzard" transmissions.  And I notice no stability problems.  It was fun  to put to use some tribal knowledge and refresh a mechanical skill.  

My Extroverted BITX40 -- On (but not in) a Box

I was going to put the BITX40 Module in a box today, but I just couldn't bring myself to do it. That board looks too good to be hidden inside a box.  So I put it topside. That's the analog VFO to the right. You can see a fan off to the left -- that is perhaps temporarily in lieu of a large heat sink for the final. You can see the two Gel cells in the background.  I am indeed running 24 volts to the final, and am putting out about 20 watts.  I had three nice contacts today on 40:  WB2RON up on Long Island said I was "20 over".  Later I worked W1SJ in N. Vermont -- I was 5-9.  Then -- icing on the cake -- DK1NO in Stuttgart.  I was 5-8.  TRGHS.

I kind of like this arrangement -- it has the "three dimensional" feel of an old tube rig.  This obviously wouldn't be good for portable operations, but I am not planning on going portable.   There is a lot of room under the chassis.   I could put a digital VFO in there and put in a switch so that I can easily go from digital to analog.

Two Gel Cells and a Heat Sink -- BITX40 Power Hack

I blame Pete for this.  And Farhan.  Pete has been leading us astray with all his talk of high power linear amplifiers ("Two 813s kid, that's all you need!").  And Farhan practically pushed us beyond QRP limits by placing a separate DC power connector for the IRF510 final amplifier on his new BITX 40 Module board.  Farhan writes: 

There are jump-points from where you can add more modules like the DDS, more bands, better audio amplifier, etc. Imagination is your limit. You can separately increase the power amplifier's supply voltage to 25 volts to be more than 20 watts of power : You will have to add a better heat sink. The mods are on the way! (from hfsigs.com)

A while back Chris KD4PBJ sent me some very nice heat sinks -- one of those would fit quite nicely on the PA side of the BITX40 board.  And I just happen to have two 12V Gel cell batteries. One will power the board and the two together will power the IRF510.  With 20 watts out to my dipole I feel confident that I will WIN the upcoming ARRL Phone Sweepstakes (in my category: Homebrew VFO, Northern Virginia).