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Author Topic: Looking for an easy to build 6 meter amp or kit  (Read 447 times)
KA3NXN
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« on: May 13, 2004, 09:13:55 AM »

Hi,

I am looking to either buy a kit or build from scratch a 6 meter amp. Primary use is SSB and I would like to have at least 500 watt output. I can go with either tube or transistor, althought I have never built anything with tubes before. Can anybody giude me?

tnx & 73's de Jaime KA3NXN
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K5DVW
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« Reply #1 on: May 13, 2004, 09:55:31 AM »

Just a comment, but if you're looking at 500W, you definately want to explore doing it with tubes first.

I dont have any plans to offer you, but the ARRL handbook used to have several VHF tube amp ideas in it. Have you done a search on their website?

K5DVW
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W3JJH
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« Reply #2 on: May 13, 2004, 09:57:25 AM »

Because of the current FCC Rules relating to amps that can be converted to CB use, you are unlikely to find a kit.

Older editions of the ARRL Handbook often contain 6m amplifier projects.  There are also some good designs in the RSGB VHF/UHF Handbook.

Motorola published several application notes for RF power transistors that have worked example designs that might fit your needs.  These ap notes are still available at www.communications-concepts.com

Ap Note AR347 covers an 800-W amp that might do the job for you.  However, the design of the 40-A, 50-V power supply is not covered, and, as a power supply design engineer, I can assure you that the power supply could be more of a challenge than the amp!  The thermal engineering of both the amp and the power supply would be nontrivial also.

Communication Concepts will not sell you a kit, but they will sell you all of the individual components, including the PC board, for the amp.

If I were you, I'd stick to a well documented project from an ARRL or RSGB source.
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N2CJ
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« Reply #3 on: May 13, 2004, 10:13:53 AM »

A popular solution for 6 meter amps is to convert a Heathkit SB-200. These amps are plentiful and typically available for $300 - $400. With a little research I am sure you find documentation on how to modify one.
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WB2WIK
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« Reply #4 on: May 13, 2004, 11:58:15 AM »

A tube or tubes is definitely the way to go for 500W output power at 50 MHz.  Cheaper, cleaner, and more reliable.

Modifying an HF amp that uses a VHF-worthy tube (or tubes) for 6m is also pretty easy, and surely far easier and less time consuming than building from scratch.

I don't agree about the SB-200, though.  Some have successfully put them on six meters, but it's quite a stretch, since the tubes (two 572Bs) are *not* rated for 6m operation, at all -- they are "30 MHz" tubes that have little gain, and are hard to drive, at six meters.

The Heath SB-220, on the other hand, with its 3-500Z's (rated for full power at 60 MHz), is a good conversion candidate for 6m.  A well converted SB-220 will run about 800W output power on six.  

An even better candidate, and one that runs just about exactly the power you're looking for, is the Ameritron AL-80B.  With its single 3-500Z, when converted for six meters, it runs about 600W PEP output power and is a great conversion candidate.  Light, small and simple, the 6m conversion process is pretty easy and the amp is available "brand new" for about $1100 -- you couldn't build a 6m 500W output amp from scratch for that, unless you happened to have all the materials on hand already.

WB2WIK/6

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M0BCG
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« Reply #5 on: May 17, 2004, 02:23:03 PM »

youre cheapest way to an amplifier on 6m is to find a heathkit SB200 .

they make between 650 and 800w output from 90-100w drive if youre local mains supply will allow 2100v plate voltage .

these amps are very stable at 50mhz so long as you beef up the anode parasitic chokes to types using 3x150 ohm carbon compound 2w resistors in each choke .

to cure the missmatch @ 50mhz  across the changeover relay just shunt feed a 0-15pf compression trimmer capacitor [350v] at the tcvr input side and with a dummy load in the output socket adjust the capacitor to show lowest thru swr .

dont bother removing 40m as per the old QST article , remove 10m and you only need to change the input tuning capacitor to a 20pf [ original 68pf] one on the input tuning side, the 10m input tuning coil stays same for 6m as per 10m .

plate coil is easy to change the tapping point from the 10m position to the new 6m position  at 1 turn round the coil from its starting point .

if you then want to go back to 10m use at anytime you only need to do a short amount of work [15mins] to re enable 10m .

id advise fitting a harbach electronics fan upgrade kit and also dont use keydown cw for tuning the amp , allways use either a tuning pulser or cw dits @ 60wpm approx .

i have successfully converted some ex cb amps to work on 6m , namely dual  6jb6a  tubed amps and also  6kd6 .
the 6jb6a also works on 70mhz very well , i have a dual 6jb6a amp running at 70mhz at 160w output for 15w drive .

the heathkit sb220 is a popular conversion and works well on 6m ,but takes a lot more work and fiddling to access various areas requiring modification for 6m use , they can put out between 600-1000w on 6m with 60-100w drive  and with suitable cooling and other modifications can be used on digital modes , i have made 4 EME qsos using mine on JT44 and  JT65B but when you start using them for digi modes it gets serious with the amount of work required in order to keep them stable at these kinds of stress levels .

whatever you buy though , if its heathkit, make sure you check closely the output bandswitch wafer contacts  [ both sides of it and very closely ]for any signs of burning out of contacts .

its very common to find the contacts burned out on the SB220  20m area and not so common on sb200 amps .

73 ian
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K7SMA
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« Reply #6 on: August 17, 2006, 08:21:20 AM »

Hello Ian,
     I've been looking to convert an old SB200 to 6 Meters. Can you send me your conversion instructions, schematics and/or pictures?  I'd certainly appreciate it.

Thank You

73

Dan  K7sma  (k7sma1@msn.com)
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