My RF Amplifier project is making progress!

The RF amplifier will work with the tetrode tube GU-84b. On the left you see the anode voltage transformer - that beast delivers 2 500 Volts at 2 Amperes in continuous service.

Current work is to program the controller that handles the operation of the power supply. The controller is based on the AVR microcontroller ATmega16 - a very flexible 8 bit CPU that can be programmed in C language using the GNU C compiler gcc in its avr-gcc incarnation ... 

All this is done on a MacBookPro using publicly available tools on Mac OS X (10.5.2 currently).

It's pure fun - I can tell you. You should try it one day... Oh, btw, the transformer weighs a woppy 52 kg.  Building the cabinet for the power supply is just about to be completed - and was not an easy task. But hey, it's just a hobby ... Now for the details -

An AVR code excerpt:

// ----------------------------------------------------
// MAIN                                                                    
// ----------------------------------------------------

int main ( int nArgc, char **ppcArgv )
{
tsREPLContext sContext;

memset( &sContext, 0 , sizeof( tsREPLContext ));
vSetREPLContext( &sContext );

// Start of controller ... so boot and init!

boot();
init();

// Controller main loop

while( 1 )
{
  repl();
}

// This point is never reached

return -1;
}

"Nothing special" you say? Well, maybe. Let's have a closer look:
  • A "context" is used - Lispers will recognize this as the environment. The context is used to hold global state and global data. This technique allows for context switches - between different modes, like "normal operation" and "service mode", by a single function call.
  • The AVR is run in interrupt mode via a timer interrupt. Every 2 ms a routine is called that reads external devices: pushbuttons, the RS232C port, the I2C bus. The values that are read from these devices are stored in the context. 
  • The REPL (the Read Eval Print Loop - also known from Lisp implementations) now reads those values, evaluates them (well, not really in the sense of a Lisp), and prints the values - which in effect means that results are written back to the devices: lamps, relays (via the I2C bus), digital and analog outputs.
Want to see more? Drop me an email!

Some more pictures:

These are the capacitor banks: 300 uF at max 5600 V. The energy stored will be around 1500 Joule. 

Actual values will be:  3240 V with 1500 Joule - Nothing to be taken lightly! 
THIS IS HIGH VOLTAGE !




High Voltage can kill - please be very careful when trying this at home!








The GU-84b tube in a test configuration. See also: http://www.sm5cki.se/ompower/testrig.html

I don't want to miss to point you to some very interesting places:
  1. Yahoo group "ham_amplifiers"
  2. Rich Measure's web site on RF Amplifiers
  3. This Japanese site is an RF Amplifier Heaven ...
Enjoy - and build one yourself - you'll have pure fun and learn a lot along the way ...

Yours truly,

   frgo.

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