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Author Topic: homebrew 6 meter amp  (Read 2896 times)
N2JXN
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« on: August 09, 2009, 04:28:20 AM »

Hello I have been home brewing small projects like power supplys and computer interfaces. I would like to build my first 6 meter amp not concerned about the output just the knowlage as to how to build it not afraid to release the smoke as they say
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WB2WIK
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« Reply #1 on: August 09, 2009, 11:49:43 AM »

Is there a question in there somewhere?
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K4DPK
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« Reply #2 on: August 09, 2009, 12:55:29 PM »

If you're looking for a place to start, get the ARRL Handbook, or the Radio Handbook (W6SAI)

If you have specific questions, let us know.

Phil C. Sr.
k4dpk
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KE6WNH
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« Reply #3 on: August 09, 2009, 05:27:30 PM »

ARRL RF Amplifier Classics has designs for several small solid state 6m linears.
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N2JXN
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« Reply #4 on: August 10, 2009, 09:05:02 AM »

Thanks I quess the question was from a homebrewing stand point with out looking at a schematic how would one start the design process. would be the tank circuit or the power supply end.
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G3RZP
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« Reply #5 on: August 10, 2009, 09:52:24 AM »

Are you looking for a tube amp, or a solid state one? How much power? How much drive have you got? You need to fix those parameters first
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N2EY
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« Reply #6 on: August 10, 2009, 09:53:53 AM »

You start out with a concept of what you want the amplifier to do.

1) What modes? (does it have to be linear, for modes like SSB and PSK31, or can it be nonlinear, for modes like CW, FM and RTTY?)

2) What duty cycle?

3) How much power output? How much drive?

4) Tube, bipolar transistor, or FET?

5) Is it for home use (120 VAC power), mobile use  (12-14 volt DC power) or both?

6) How important are size and weight?

7) What resources do you have to build it (junkbox, test equipment, tools, circuit board fabrication, etc.)

Cool What existing designs have you examined to see if one of them fits your needs?

The answers to those questions are the starting point.

73 de Jim, N2EY
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WB2WIK
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« Reply #7 on: August 10, 2009, 10:42:53 AM »

>RE: homebrew 6 meter amp       Reply
by N2JXN on August 10, 2009    Mail this to a friend!
Thanks I quess the question was from a homebrewing stand point with out looking at a schematic how would one start the design process. would be the tank circuit or the power supply end.<

Since you said "tank circuit," it sounds like you want to build a tube amplifier.  If so, before doing anything decide what tube or tubes you want to use, as everything else (tank circuit, power supply requirements) will be governed entirely by that.

The ARRL VHF-UHF Manual and the RSGB VHF-UHF Handbook both have construction articles for six meter amplifiers.  The older ones have mostly tube type amps using 3-500Zs, 4CX250s, 3CX800s, 8877s, etc. in the 500W to 1500W output range.

WB2WIK/6
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N2JXN
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« Reply #8 on: August 10, 2009, 03:50:13 PM »

Thanks thats what I was looking for a place to start. And yes I would like to do a tube amp. As a start would like to do somthing like 500 watts.

So looking at this as a starting point what tubes would you recomend.

I will be getting both of the manuals you have recommened.

As for test equipment I have a 100 meg o'scop,rf generator,function generator, dvm, lcr meter,both dry and oil filled dummy loads,hv probe, 2 bench power supplys. what else would you recommend for test equipment to be used on a project like this
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K4DPK
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« Reply #9 on: August 10, 2009, 06:40:10 PM »

Well, if you have an exciter in the 50-100 watt class, you’ll want to run something grounded grid, cathode driven.  You can pick from either glass envelope or metal/ceramic.  Two tubes that come to mind are the 3-500z and the Russian GI-7B.  The GI-7B is the cheaper of the two, and probably the more readily replaceable if need be.

In your design, you have six distinct areas to consider:

The input network
The tube and cooling it
The output network, probably a pi-net
The filament, bias, metering and control system
The power supply
The enclosure and metalwork

Decide what bands you want to operate, and begin your design.  Start with a block diagram, and list all the parts you’ll need inside each of those blocks.

The frequency and power level will dictate the properties of the parts.

Obtain your chassis and all the major large parts, and begin what I call “playing chassis chess”.  

Don’t mount anything until you have ALL the major parts.  Otherwise, you will always have to move something after you get it mounted, and you’ll have extra holes in the chassis or panel.

In your layout, keep two things in mind.  Keep all your RF leads as short as possible, and make the chassis and panel as ordered and cosmetically pleasant as you can.  Always mount parts at right angles, parallel to the walls of the chassis.  Nothing looks worse than a diagonally mounted jumble of clutter under or on top of a chassis.  Same goes for wiring and cables.  As much as possible, keep the front panel symmetrical, even to the point of using right-angle drives and longer than normal switch shafts.  The only thing better than a project that works well, is one that looks great, too.

Anything you need to adjust, like input networks or bias controls, should be accessible without getting near the HV, and preferably without removing covers.  I always try to mount these on the backplane.

As much as possible, test each division of the circuit as you complete it.  Don’t wait on a surprise to bite you when you think you’re finished.

I didn’t intend to get this long-winded.  Maybe it would have been better as an article.  I'll stop here.

If you get this far and then have problems, we’ll iron them out as we get there.

Phil C. Sr.
k4dpk
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K4DPK
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« Reply #10 on: August 10, 2009, 06:52:56 PM »

BTW, you have all the test equipment you'll need except for maybe a noise bridge or an MFJ-259 or the like.

Phil C. Sr.
k4dpk
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G3RZP
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« Reply #11 on: August 11, 2009, 05:43:46 AM »

If you haven't worked on a tube amp, just remember that it uses lethal voltages. The power supply is no 5 minute job, either.
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WB2WIK
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« Reply #12 on: August 12, 2009, 11:59:18 AM »

If you're interested in a slightly more ambitious project for 6m, you could try building my 4-1000A amp design.  It produces 1500W PEP output with just 20W drive and was published in 73 Magazine, July 1985 issue.

I have a .pdf of the article if you're interested, I'd just need your e-mail address to send it.

It's a "heavy" project but not a complicated one, and the tube is very robust and they are easily found on the surplus market for only about $100-$150 (used pulls, still good for amateur work).

WB2WIK/6
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K4DPK
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« Reply #13 on: August 12, 2009, 09:00:11 PM »

Hey Steve,

I'd like to see the schematic of your 4x1

Thanks

Phil C. Sr.
k4dpk
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WB2WIK
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« Reply #14 on: August 12, 2009, 09:06:43 PM »

Phil, I've received a number of requests now and will bulk mail them all tomorrow from the office where I have a 100Mb/s+ connection.  All will fly out tomorrow morning (Pacific time).

73

Steve WB2WIK/6
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