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Author Topic: Amp Building Questions????  (Read 1711 times)
VE9KAR
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Posts: 20




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« on: January 29, 2004, 09:31:11 PM »

I'd like to homebrew an amp, But never having done this I find very little info available on Homebrew amps, Thinking of building an amp for 6M, 400-500 watts, maybe 4cx250's?? Can anyone point me in the right direction, Not in any great hurry,I want to understand what I'm doing,  any books articles etc much appreciated
VE9KAR
Kent
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KA0RKB
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Posts: 4




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« Reply #1 on: January 30, 2004, 12:38:49 AM »

Go to:  http://www.w8ji.com/ and click on amplifiers.
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WA9SVD
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Posts: 2198




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« Reply #2 on: January 30, 2004, 12:52:27 AM »

Check some of the ARRL Handbooks, and back issues of QST.  You can probably get many at your local library, or from inter-library loan.  

    One specific:  ARRL 1978 Handbook, had a project for a 6M 4CX250B amp requiring only 10W. drive.

Good luck, and have fun building and operating!
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WB2WIK
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Posts: 20595




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« Reply #3 on: January 30, 2004, 12:44:46 PM »

4CX250's are great, small, inexpensive, popular and have tons of gain under normal bias conditions; however if you have a 100W exciter, this tube's a poor choice because you'd need to throw away about 95% of your drive power.  (My dual 4CX250B amp on six runs 1.0 kW CW output power with exactly 6W drive power.)

The 4CX250, being a tetrode, also needs four power supplies to function: Heater, grid, screen, and plate.  So, it's power supply can be a bit more complicated (and heavier, and more expensive) than that required for a triode.

You might be better off with a 3-500Z, especially if you have serious drive power (50W or so) available.  That tube only requires filament voltage and high voltage for the plate, making for a much simpler (and often lighter, and lower cost) power supply.

In any case, the ARRL VHF-UHF Manual, as well as the U.K. equivalent book published by the RSGB, both contain useful circuit designs and full construction plans for vacuum tube power amplifiers for 50 MHz.

I also published two construction articles for KW amps for six meters: "Build the Block Buster" is a 4-1000 amp for six that runs 1500W PEP output with about 20W drive, and was the subject of a major construction article in 73 Magazine, c. 1984; "The WB2WIK 8877 Six Meter Amplifier" is an 8877/3CX1500A7 amp for six that runs 1500W PEP output with about 75W drive, and was the subject of a major construction article in CQ Magazine, c. 1985.  They both work well, and dozens were reproduced by hams worldwide, based on comments received over the years.  I still have the 4-1000 six meter amp, but sold the 8877 amp to WA2VUN many years ago.

73 & good luck!

WB2WIK/6
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VE9KAR
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Posts: 20




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« Reply #4 on: January 30, 2004, 04:11:09 PM »

Thanks for the Replys, Great info, I should add My 6M rig is an Alinco dx70th, 100 watts on 6M, or low power 10 watts, here is a further adjustment(internal) that brings it down to 5/50 watts, I cannot vary the output from these figures. I would prefer to use either 10 watts or 100 watts as the drive power as I also use this rig for HF and don't want to open and change from 5/50 to 10/100 every time I change bands.so this limits my options for drive power to either 10 or 100 watts. I'm a little timid of running a kw as I live in a fairly populated area and am nervous of TVI etc, I was thinking 400-500 watts would give me that little extra drive for Au or tough conditions. I've been pretty succesful with 100 watts, but on occasion feel I could use a little more power for marginal conditions. My antenna is a 5Element homebrew on 17' boom at 55' on a Delhi tower fed with about 150' Rg213.
Kent
VE9KAR
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WB2WIK
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« Reply #5 on: January 30, 2004, 08:21:56 PM »

For ~800W PEP clean output power (driven by a 100W PEP source), a single 3-500Z would do the job very well.

I would not recommend a 4CX250 or a pair of them when you have an Alinco for an exciter.  If the Alinco ever *accidentally* transmitted with 100W of power into the grid(s) of 4CX250(s), you'd have some very expensive fuses on your hands that would be nothing more than paperweights from that moment forward -- even if the accident lasted all of ten milliseconds.

VE9 should be a *great* place to work 6m!  You are certainly 3000+ miles closer to the Au zone than I am, and I miss working 6m Au.  Say "hi" to the gang up in VE9/VE1 for me, I miss them, too!

73 es CU on 6...

Steve, WB2WIK/6
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KQ6EE
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Posts: 4


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« Reply #6 on: February 06, 2004, 06:19:09 PM »

Hi:
  Check the web site www.nd2x.net, and click QRO. You will find a lot of GOOD info about amplifier specially Russian tubes which are much much cheaper than others.  You can buy or bid some tubes at ebay.  Many Russian tubes do not need some of those expensive socket.  If you are the builder, you can make your own socket.  Good luck, and make some fun to build your amp.  Tell me how's going at kq6ee55@yahoo.com 73

                                                         Hon Chu
                                                  in Southern CA
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KC8YXA
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« Reply #7 on: February 09, 2004, 09:58:11 PM »

I dont want to start a fight but tubes are getting harder to find these days transistors are the way to go there smaller easer to cool . On the down side tubes are a little more forgiveing than transistors
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WB2WIK
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Posts: 20595




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« Reply #8 on: February 10, 2004, 02:51:11 PM »

KC8YXA, on the *really serious* downside, transistors that can run as much power as tubes need to operate at voltages much higher than 12V (typically, about 50V) and can cost far more than tubes, by the time the cost of the 50V power supply is considered.

Amplifiers that use 12V transistors cannot produce more than modest power with reasonable IMD.  To run legal-limit power on the amateur bands, it takes high voltage transistors that can easily cost $150 each.

WB2WIK/6
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SSBDX
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Posts: 1




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« Reply #9 on: February 19, 2004, 10:52:50 PM »

This discussion of solid state amps is stupid.  50KW broadcast amps use modules with low voltage rocks.  The collector voltage is irrelevant to power out. Using any number of modules is possible.  Connecting 10 150watt output 12v amps is no problem to produce 1500watt output.  I personaly use 8 300watt 28volt amp modules to put out 1.5kw.
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N0RTU
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Posts: 27




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« Reply #10 on: February 20, 2004, 10:29:18 AM »

Hello Kent

I'm not going to debate tube vs. Solid state here.  They both have advantages and disadvantages.  Tubes have been used for ever and you shouldn't have much trouble finding info on building for whatever power level you'd like.
Transistors and FET's are gaining popularity however but they have some issues (filtering and suppression) that can be dealt with.  
I'm anticipating the same project as you right now and I'm doing my homework before I invest a penny.
Tubes are great.(the 3-500 is very tempting)  Transistors may be better depending on your situation. (some of Motorolas MRF series transistors can be had new for 20.00 each depending on your requirements.)  I'm reading up on both.
Do a google search for "motorola application notes" and you'll find some interesting stuff on amps using the MRF transistors.


73
Mike
N0RTU
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SSBDX
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Posts: 1




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« Reply #11 on: February 20, 2004, 12:40:34 PM »

Just a historical note.....Alot of new hams aren't aware that hams missed the high power solid state revolution 2 decades ago.  When the military was still into hf, vhf, Motorola developed their high power MRF line in late 1970's.  Although there was always some attempt to produce high power solid state amps for hams, it never really caught on.  By the late 1990's, the military dumped hf on a large scale and Motorola sold their MRF line with others to ON Semiconductor.  Their sales were poor for solid state high power anything.  Motorola is almost totally out of the general semiconductor business.  

I can't remember for sure, but it seems I heard that ON semiconductor filed for chapter 11 or is just in bad financial condition.  There is little market for descrete transistors by high volume manufacturing standards.

Hams still favor tubes and that is a shame.  Solid state high power amps are really cool, but there never was the info available like there is about tube amps.

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