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Author Topic: CB to Ham Amp.  (Read 1000 times)
W2BPI
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Posts: 6




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« on: August 23, 2004, 06:50:33 PM »

What would it take to convert CB amp. To work on 40 meters. Tnx  George/W2BPI
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W9GB
Member

Posts: 2577




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« Reply #1 on: August 23, 2004, 09:48:44 PM »

George -

This topic appears with such frequency I think it should be added to all amateur examinations.  
http://users.aol.com/rfelectron/faq.htm

I have no idea what type of amplifier (e.g. tube, solid-state, mobile, fixed base) you are considering for conversion to the 40 band.

My short answer is it MAY be useful for parts to build your own -- but this would be for your educational, learning and building enjoyment (e.g. It is NOT based on economics).

There are plenty of very good HF amplifier designs on eBay and for sale on a weekly basis at good prices -- that already work.

Look at eHam.net reviews and "check around" before purchasing any amplifier.  A good Google.com search will quickly imform you for the preferred tubes (NOT sweep tubes) or solid-state models in the marketplace.

What makes a good solid-state amplifier? (Adam Farson actually has a web page for a bit of theory and to understand "Why Not?"
http://www.qsl.net/ab4oj/quadra/sshfamp.html

What makes a good tube amplifier?
http://www.qsl.net/kk5dr/goodamps.htm

w9gb


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WB2WIK
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Posts: 20536




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« Reply #2 on: August 24, 2004, 05:35:08 PM »

It's incumbent upon hams to meet the technical requirements of Part 97, and since we're allowed to homebrew amplifiers from scratch, obviously we're also allowed to modify stuff to our heart's content.  But it's still incumbent upon us to meet technical standards that most of us, unfortunately, can't even measure.

For that reason alone, it's probably a better idea to stick with "certificated" RF amplifier products, which are the ones on the market designed and sold by regular amateur equipment manufacturers.  Those amplifiers, so far, all have bandswitches which are there for better purpose than to fill a hole in the front panel.

Unfortunately, "low drive" amplifiers for the HF bands have been unlawful to sell in the U.S. for about 25 years or so.  That makes it difficult to buy an amp that can be driven by a QRP rig, even though this is a perfectly legitimate application.

However, there is a rulemaking notice already written (but not enacted) that would change this, and provide for U.S. sale of "low drive" RF power amplifiers in the HF spectrum, including 15-12-10 meters.  (Obviously, the reason these were "outlawed" in the first place was an attempt to prevent CBers from using ham amplifiers to run illegal power on 27 MHz.  The attempt basically failed, since dozens of manufacturers of illegal CB amps sell their wares daily, all over the place.)

So, if you just wait a while, this will probably become legal and there should be some good products (made for hams) on the market pretty shortly.

WB2WIK/6
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K4DPK
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Posts: 1077


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« Reply #3 on: August 25, 2004, 08:01:54 PM »

George,
If it is a solid state amp, it probably already will operate on 40m, but since it won't have adequate low-pass filtration it will be transmitting out-of-band harmonics.

If it is a tube amp, you should know that the resonant input and output networks would need to be tuned to the 40 meter band.

Get an ARRL Handbook and read it.  By all means, get involved in homebrewing.  

73
Phil C
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N5KBP
Member

Posts: 287




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« Reply #4 on: September 06, 2004, 06:15:15 PM »

What kind of amp is it? Solid state or Tube?

N5KBP
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