New 2 meter EME amplifier..

[VK3ZL]

Hi all...About a month ago I was asked if I could build a 2 meter RF amplifier capable of delivering 400 watts EME data...This means one minute on and 1 minute off data transmissions, quite a task for any amplifier...It needed to be reasonably compact and straight forward and practical..

Most of my amplifier experience is with HF amplifiers, having built more than 50 over these past few years so I was able to come up with a few ideas and apply them to this project..

I chose a Russian GS-31B triode for the job....This tube has a 1kw anode dissipation, grid dissipation of 26 watts and a maximum cathode current of 1.4 amps....I chose an anode voltage under load of 2.5kvdc...

The next problem to solve was how to blow off the 400 watts of plate dissipation whilst delivering 400 watts continuous RF data....The GS-31B has a solid cast alloy removable finned heat sink type cooler...The air through this tube is basically free flow with little to no back pressure...After a few inquiry's from some experienced ham buddy's I chose a new EBM Papst 4650X all metal boxer fan for the job..I had to import some from the US at considerable cost, mainly postage...

I chose a very straight forward T output network using a machined aluminum disc capacitor for tuning and I then machined up an adjustable coaxial pickup for loading....This pickup is a set and forget feature...

The power supply is a conventionial voltage doubling unit using a large toroidal HT transformer especially made for this job...The HT supply is 3kv peak dropping to 2750vdc under an 800ma load...I hand wound a filament transformer, 12.8 volts @ 4 amps and used a commercial small tranny for the 24 volt relay supply..

The amplifier is simple using manual switch on for the heaters and HT supply and has a variable bias control..Anode and Grid current are monitored using a pair of cheap but good quality meters...I made my own scales to suit the job...

The complete amplifier is hand made from the case to the front panel finish and the various boards wiring etc...The job probably took around 30 hours to complete over the past month....It has been an enjoyable project and gained me some new experience and knowledge which I will apply to the next project....

Simple specs....The amplifier will easily run 1kw output SSB and CW..For 400 watts data the amplifier runs loaded 2700vdc @ 300ma...As the efficiency is nearer 55% there is some spare overhead....Weight 18kg... Case 18" wide x 16" deep x 6.5"high

Enjoy the construction pictures...

Bob..VK3ZL..

[VK3ZL]

More construction pics..These show the case under construction, the tube socket and input T network shielded box, and the finished amplifier module...The complete module can be easily removed from the amplifier case simply disconnecting HT, Filament and B minus wires and coax connectors....

Bob..VK3ZL..

[NQ6U]

Damn, you're good, Bob!

[PA5COR]

VHQ ( Very High Quality as usual Bob...
Thanks for sharing, love your work and pictures.

73,
Cor

[KG4CGC]

Always amazing.

[KA5PIU]

Hello.

Tubes!
I can run around 300 watts with the finals section from a 330 watt radio, all solid state no tune.
But, a am somewhat of a sloppy builder, nowhere near the effort or quality of that thing!
In fact, I am noted for simply drilling and tapping, sawing and bending, to produce the end product I want, if it works I am happy.
In order to make it look nice I have someone who does woodworking build the wooden box it goes in, that is if it is ever made to look nice. ;)
Casa de Rudolfo, home of the 'Make it work and paint it blue'.

[W7XF]

Uhhhhhh Rudy...

For data duty, you should not run a solid state amplifier (or ANY amplifier, at that) at much more than 50% rated output power; the high duty cycle of digital modes (excepting CW) will QUICKLY overheat and/or fry components, no matter how efficient the cooling system.

[KG4CGC]

Uhhhhhh Rudy...

For data duty, you should not run a solid state amplifier (or ANY amplifier, at that) at much more than 50% rated output power; the high duty cycle of digital modes (excepting CW) will QUICKLY overheat and/or fry components, no matter how efficient the cooling system. Could you use an APU for cooling?

[suddenseer]

Bob, you are an awesome radio amateur. :bowdown: I have only made a few qrp tx's. I had amassed junk to make an amplifier, but never quite got to your level.:ashamed: Your beautiful gardening skills seems to balance you as a person. Are you a good cook as well? I wish you could adopt me.:lol:

[KA5PIU]

Uhhhhhh Rudy...

For data duty, you should not run a solid state amplifier (or ANY amplifier, at that) at much more than 50% rated output power; the high duty cycle of digital modes (excepting CW) will QUICKLY overheat and/or fry components, no matter how efficient the cooling system.

Hello.

This is 100% duty cycle commercial repeater amplifier we are talking about, not some wimpy ham effort. ;)
330 watt repeaters are being replaced by the digital counterparts.
As a matter of policy the frequency determining elements and sections are being removed and crushed.
This leaves a really nice cabinet with a set of duplexers and a massive battery backed power supply, and one hell of an RF section.
2 watts in, 330 watts out. ;)
But that is just the policy, the stuff can not be put back on frequency.
It makes as much sense as the cash for clunkers program, that said the "clunker" could not be over something like 10 years old.

[KC2UGV]

Gorgeous. Absolutely gorgeous craftsmanship.

[KA5PIU]

Hello.

Yes, the quality is far better than anything I do.
Gardening? anyone up for a backhoe, it is me! ;)

[mw0uzo]

I think some love juice just leaked out. Awesome amplifier!

[kc5yhq]

Do u have a simply drawing and item list so a person can build the amp.. I want it for my personal use.. thanks
kc5yhq@hfradio.org

[N8YX]

Bob,

What's the tuning procedure for the "loading" disc - and is it accessible when the amplifier is under power and operating?

[VK3ZL]

G'day John,the loading disc is a set it and forget it unless you want to drastically move frequency..It is adjusted by loosening two grub screws...I just put a plastic tie around the N type elbow and through a hole in the side of the case...With the cover back on the box it is a simple job adjusting loading moving the plastic tie carefully in and out...Once adjusted for best output, remove top cover and tighten up the two grubscrews and cut off the plastic tie...This amplifier is generally used on 144.250 and the loading is set up around 144.200...A quick peak of Tune seems all that is required from 144-144.300...The ham only uses it for EME work and the rare ssb contact....We ended up installing an extractor fan, (Papst 4650X above the tube to add extra assistance to air flow so the unit has a push pull air system...This is quite adequate for 1 minute 400 watt data bursts without getting too warm...Noise is minimal mainly the air flow....I am now doing a 432mhz version, simple circuit and once more aiming for 400 watts continuous power out data bursts...The 2 meter amp easily does 1 - 1200 watts cw and ssb...

I prefer to build simple and reliable amplifiers with no bells and whistles...These are "Real Operator's " units..

Bob..VK3ZL..