linear cookbook

[snow bird]

Unit 339 When I try the web site you Posted I get a merssage from Microsafe that the Page is Un safe to use

 

[kopcicle]

And then ...

Motorola EB boards were NEVER intended to be production boards. As built and sold from the Motorola engineering kits, they have extraordinarily high peak drain voltages on some bands. This is NOT, or was not in my careful tests, a parasitic. It was a simple harmonic resonance in the foil traces from the FET's to the transformer. The transistor drains are loaded with a very high impedance and so any harmonic energy that falls on those resonances with add a short peak that rides on top of the normal positive drain voltage swing and exceeds the drain to gate breakdown voltage in some FET's.

This is why some amplifiers will seem to be fine, while others occasionally fail. At least this was my experiences when making actual load pull tests.

Of course I can't say something someone else builds will never oscillate, but I never ran into that.

I don't know why people assume those are optimized production boards. They are not. All of the EB series are really just things that were originally intended to give a starting point for engineers.

note:

I never used the Motorola boards without input swamping.

Ameritron does not use something similar to that board configuration (I never used the exact Motorola board in Heathkit or Ameritron or medical applications for several reasons all associated with reliability, and now I moved they entirely away for the concept in that board) or the transformers, because the boards and transformers were nowhere near optimum.

73 Tom W8JI

My own experience mirrors this. I can also verify from the original source that "the EB series are really just things that were originally intended to give a starting point for engineers."

I'm not knocking Motorola or Helge , far from it. The EB104 was/is a great starting point.

 

[kopcicle]

@snow bird HERE
http://www.communication-concepts.com/eb104-1/

 

[unit_399]

I never suggested that this kit was "plug and Play." Since 30 mhz is at the top end of it's band width, it will require circuit changes to max its performance and reliability at 27 mhz ( if that's its intended operating frequency.) Also needs TX/RX switching, power supply filtering, proper biasing, etc.
But, for an experimenter, the kit is a great place to start as K6ZOA mentioned. And ... having a circuit board and all the components makes getting started a lot easier.
With GOOD high power bi-polar RF power transistors becoming nearly extinct, development of reliable high power FET-based amplifiers is the way of the future.

- 399