Latest enterprise..GS-31B 6 meter amplifier..

[VK3ZL]

Gidday all..I have been keeping busy these past few weeks...I delivered a new GS-31B 2 meter amplifier to a friend a month ago and he asked me if I would build a 6 meter twin..I got to work a couple of weeks ago and put this one together...Pretty straight forward with no bells and whistles, just the old homebrew Heathkit style..

The amplifier has soft start for HT, adjustable tube bias from the front panel and other normal controls..The HT transformer delivers 1300vac @ 1.5 amps CCS...It is voltage doubled and gives around 3500vdc...Minor supply's are 24vdc for relays and 20vdc for the cooling fan...I used a Papst 5 inch 12-28 volt fan for cooling...This fan produces around 225cfm in free air and is more than adequate to cool the GS-31B tube...The RF deck is pressurised and the air goes through the tube cooler and exits through a Teflon chimney on the top cover..

The amplifier uses a simple Tuned T input network on the cathode and a Pi-L network on the Business End..I built the case so that there is plenty of room under the hood for maintenance and easy servicing...The front panel hinges down to expose the main control wiring etc...All wiring is color coded for the various amplifier circuits and functions...

I set this amplifier up on the test bench last Monday morning and gave it a run...The amplifier tuned up perfectly first try and I only had to tweak the T input network variable capacitor..Bypass vswr is 1-1...Drive vswr is 1.2-1...I ran the amplifier up to 1kw output with around 45 watts drive, didn't bother driving it any harder....The owner only wants a reliable 500 watts in all modes....This amplifier does the deal..

Delivered the amp this morning and one really happy owner...I like it when things go well..

A few pics....Enjoy..Bob..VK3ZL..

[VK3ZL]

Rest of the amplifier pics..

Bob..VK3ZL..

[KG4CGC]

Radio Porn.
No really. I mean porn in a, good, way.

[kb2vxa]

Aw reet!

[PA5COR]

Beautifull as ever, a work in progress...;)

[NQ6U]

Radio Porn.
No really. I mean porn in a, good, way.

This. Fucking A.

[K7SGJ]

Another outstanding job, Bob. I may have asked before (I'm old) but, how do you produce the front panel artwork?

[VK3ZL]

Another outstanding job, Bob. I may have asked before (I'm old) but, how do you produce the front panel artwork?


I use dry rub on letters and give the panel a spray of clear lacquer when I finish...

Bob..VK3ZL..

[K7SGJ]

Thanks. They really do turn out nice. Good job!

[koØm]

I use dry rub on letters and give the panel a spray of clear lacquer when I finish...

Bob..VK3ZL..

Bob, what all metal working tools do you have in the workshop? Break, Shear, Standing Drill press, miter saw? Any, all; what else?

.

[K7SGJ]

Just two files. A flat bastard, and a round MFer.

[VK3ZL]

Closer to the truth than you realise...I have a drill press which I purchased 35 years ago...I can use a 1mm drill in it and the chuck still runs perfectly true..Let's see, yeah about a dozen or more flat bastards of various cut, some half round and round files..Two electric hand drills one battery powered..I have two metal squares probably 90 years old which were my fathers..Dozens of drills of all sizes metric and imperial..I cut all my metal, ie aluminum angle by hand with a hack saw and vice...There is an art in this which has to be mastered..Pop riveter..I use all 1/8 inch dia rivets 1/4 to 1/2 inches long..

I have all my aluminum sheet cut in a metal fabrication shop these days...I then build up the cases using 12mm aluminum angle..I assemble the whole case using nuts and bolts to make sure everything is in alignment then remove each bolt at a time and replace it with a pop rivet...

To make large holes for meters fans etc I scribe the size on to the aluminum panel...I then scribe a second circle 1/8 inch less diameter...I then proceed to drill out the hole using the inside scribed circle...Once complete I knock out the center and carefully file the left over edge out to the scribed circle..

Smaller holes for coax sockets, high voltage feed thru bushes, grommets etc, I use a step drill..I then use a tapered reamer to finish the hole to size..

The front panel finish is a bit complex...I use a strip of half inch aluminum square tubing top and bottom of the panel..I step the top piece 3/32 inch above the panel so that the aluminum cover fits flush...The rest of the job is just plain hard work needing patience and care...Remember the old saying, "Measure twice and cut once" ..Those of you who work in metal or wood know what I mean..I always try and finish an amplifier with no extra holes or mistakes..I have become adept at masking these of course..Stick a bolt or pop rivet into a wrong hole and usually nobody but me will notice...However I always try to avoid mistakes..

Most of my amplifiers are simple and uncomplicated...I do not use overload control or automatic starting circuits...Being of the old ham school I believe in plain hands and eyes on operating....If you are watching your meters etc when operating, then apart from some bad component failure it is easy to pick up any problem that may be developing in your amplifier...

Ok, off the soap box now....Bob..VK3ZL..

BTW I have just started on a new 2 meter GS-31B amplifier today...Working on the case now and will have it done over the weekend..

[W3WN]

I wish to blazes there was a practical way for you to build me an amp... and get it here without it costing a small fortune.

Dayum, you do good work.

[K7SGJ]

I wish to blazes there was a practical way for you to build me an amp... and get it here without it costing a small fortune.

Dayum, you do good work.

Well...........there might be a possibility of a Bobkit.

[koØm]

Well...........there might be a possibility of a Bobkit.

You know, what Bob has going for him is a system, a "Bobkit" would not really be a stretch for him to produce. He could supply the sheet metal sides and angle, a finished face plate, etched copper boards that he mounts components, switches, connectors, relays, pictures and a diagram. You supply the wiring, transformers and other power supply parts and, the tube.

I have looked carefully at Bob's construction techniques and, I am going to incorporate some of them on a couple of projects that I have to finish.

.

[VK3ZL]

Hi all...I have been held up waiting for some parts for this amplifier...At last everything has arrived and I was able to complete the project over the past few days....The amplifier is now switching on, all functions operating properly....I will start some RF tests this week and expect this one will be ready for the new owner..

First batch of pictures are the HT transformer and the etched rectifier board and the completed rectifier pack...This is a voltage doubler...The HT transformer is rated at 3Kv AC 1.5 amp CCS which when rectified will produce around 3400vdc..These Toroids are good quality and cost me around $300 including shipping..

Enjoy..Bob..VK3ZL..

[VK3ZL]

Next lot of pictures are the completed amplifier...I don't paint the top cover and amplifier sides until all is complete and the amplifier fully tested with RF..This unit will produce 1kw CW and SSB and 5-600 watts EME data work..

Not sure if I included some tech details of this amp in earlier posts..The amplifier uses a tuned T input network to the Cathode...The output RF deck is a tuned 1/4 wavelength line grounded at the far end..I use a 20kv 330pf HT blocking cap on the hot end of the line...The line is tuned using a simple Flapper capacitor cam driven from the front panel...The Loading is a short tunable pickup link also tunable from the front..This job was requested to use ordinary PL259 sockets...I had a 12 volt Belling Lee coax relay and fitted it all up...Works fine with 24 volt through a dropping resistance..

You will note the space under the hood for easy access to everything for servicing.

I will take another batch of pictures once I have the amplifier running and complete..

Enjoy....Bob..VK3ZL..

[VK3ZL]

Hi all..I posted these last two replies into the wrong thread..They belong in the 2 meter amplifier thread..Sorry...

Bob..VK3ZL..