designing Class C qrp amps

Discussion in 'Homebrew and Kit Projects' started by VA7AAX, Nov 17, 2008.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: Left-3
ad: abrind-2
ad: L-MFJ
ad: Left-2
ad: L-Geochron
  1. W8JI

    W8JI Ham Member QRZ Page

    It may be past protection now, so someone might grab it.

    I'll suggest to MFJ they look into priniting and selling it. They did "Antennas and Transmission Lines" by Kuecken that way. That's one of the best moderately advanced antenna handbooks ever made.
  2. K5UOS

    K5UOS Ham Member QRZ Page

    Some things don't change

    I remember when I was making the transition from homebrew tube to homebrew solid state. I received a gift copy of Solid State Design from my dad, W1KPS (SK). As Tom infers, certain principles don't change. There are two notable sections that I personally believe are timeless and useful today. There are other sections that are useful but a couple pertain to this thread.

    Chapter 4 in SSD has straight forward information and design formulae for Matching Sections which I have adapted to circuits in both solid state and tube gear. This thread was about designing Class C amps. I have a comfort zone using L-C-C networks to match lower level stages to a PA gate or base input and for the low impendance drain or collecter to 50 Ohm low pass filters for power amps in the 10 to 50W range. I also use the Pi Network formulas for filters from 25 ohm to 500 ohms with the latest being 500 ohm filters for 3 discrete solid state oscillators for use in a hybrid homebrew tube receiver front end. The L-C networks have been useful for terminating crystal filters.

    I set up most of the SSD formulas in an Excel sheet that I have been using for 20+ years.

    Another classic circuit in Chapter 2 shows the Universal QRP Transmitter. This was interesting to me back in the late seventies when transitioning to SS because it was essentially a solid state example of the old 6AG7/6L6 MOPA. I can't think of a better 1st project than this...well, maybe a 6AG7/6L6...but a different thread.

    Lastly, the receiver in Chapter 5, P102, was an early favorite of mine as it resembled the tube 40/80 meter Handbook receivers I built in my early homebrew tube days. The dual gate mosfet may be a bit harder to find but remains a reasonably popular device for homebrewers even today.

    Note: On page 104 there is a receiver that uses the same IF amp (MC1350P) that the much heralded K2 uses decades later.

    All this said and second hand prices for SSD being what they are, the more modern EMRFD is a great buy for the price. Much of the same timeless information and certainly a rich collection of circuits to keep any serious homebrewer/experimenter busy. Both books were written for the ham who was not a graduate engineer but made the decision to build some or all of his /her gear. I believe buying either is an investment not an expense.

    One thing I like about EMRFD is that it often avoids absolutes. A section on IF amplifiers may progress through many device types and configurations without stating which is the best but relating the various strengths and weaknesses and leaving the choice up to the reader.

  3. W4HAY

    W4HAY XML Subscriber QRZ Page

    I don't know if it's still available, but the Sam's Publications RF Circuit Design by Chris Bowick is also good. CAUTION: If you're queasy about Smith Charts and S-parameters, this one will positively terrify you!
  4. VA7AAX

    VA7AAX Ham Member QRZ Page

    HAY, I think i want to stay away from Smith Charts!(though, n0ax has 3 columns about it in his Hands0n radio column,might read up on that)

    Well, yeah, I have heard of SSDRA. but yeah, they sell for collector's prices.;)

    Christmas is coming so let's keep our fingers crossed.

    A homebrewer without EMRFD is like a HAM without radios!

    Recently, I was given the SPRAT CD v2 on "permanent loan" basis. It has issues 1-109 and I have been enjoying that too . A very cool read indeed!
  5. VA7AAX

    VA7AAX Ham Member QRZ Page

    The RF Circuit Design by Chris Bowick is available (2nd edition) through amazon for $40
  6. KL7AJ

    KL7AJ Ham Member QRZ Page

    Yes...and you'll have to pry my copy from my cold dead bony hands. :)
  7. KL7AJ

    KL7AJ Ham Member QRZ Page

    Just realized that "Fine Business" has been a silent key for over a decade. I must be getting old. :)
  8. KA5LQJ

    KA5LQJ Ham Member QRZ Page

    The "Good Ol' Daze", LOL!


    Please indulge and old man. As best I can remember, "Class C" amps, "swung" something like 80 to 90% of the "duty cycle" and were used to amplify AM transmitters back-in-the-day before less scrupulous Class D "operators" started using them, ruining it for everyone else. :mad:

    I happen to be the happy recipient of a 1950 edition of Editor's & Engineer's Handbook. :D Sadly though, due to my disability check, I can only dream of getting the parts together to build one of those AM amps. :(


  9. KB1LQD

    KB1LQD Ham Member QRZ Page

  10. W4CBJ

    W4CBJ Ham Member QRZ Page

    Yep, I find that some of the older books have 'good stuff' that the newer ones don't. One of mine has a simple explanation of the " J" operand. If I can find it....I will post it on the QRZ forum. How many people would be interested or could even understand this ? In the event that you may need funds for republishing an old radio can find me at the nearest homeless shelter. 73 Joe W4CBJ
    Last edited: Nov 24, 2008
Thread Status:
Not open for further replies.

Share This Page