Amplifier re build..

[VK3ZL]

Hi all...I have been busy these past few days doing a re build on my old HF shack amplifier..I built this unit a few years ago to cover 80-10 meters but in all that time I only ever used it on 7mhz..As my building and wiring skills have improved I pulled out all the original wiring, grid protection circuits and the tuned input and pi output coils...I made up a completely new front panel..

I completely re wired the amplifier using my current style, and disposed of the grid protection circuits which I have found unnecessary with the Russian GI-7BT triodes...I made up a simple adjustable Pi input network and a new coil for the Pi output...

I started on Monday and finished today...Switched it on and all functions work perfectly..I havn't put any RF into it as yet as I am re vamping my shack...Needed a good cleanup..

The following pics are the old amplifier then the rest the finished overhaul..Enjoy..

I will now upload the re modeled amplifier..


Bob..VK3ZL..

[VK3ZL]

Ok This is the completed 7mhz 2 x GI-7BT amplifier....If you look at the tubes you will see that I have used coolers from GI-46B tubes....These coolers are much more efficient than the originals and are a perfect fit..Pics show the re vamped Pi network with a simple home brew coil..I retained the vac cap 3-200pf and the 3 gang loading cap..Behind the front panel is all new wiring..Step start and bias control circuit etc..

I am really pleased with the outcone...Downer is that there are a few spare holes in the chassis but a few bolts and nuts, pop rivets etc will cover them up...

I have included a pic of the HT transformer...It came from some old industrial equipment..Beautifully made C core..Secondary is rated 900 volts at 1.5 amps..Voltage doubled it gives around 2450 volts and drops 150 volts under an 800ma load...Picked it up for $5...I just wish there was more of that stuff around...

Ok that's all of that project....I am also about to complete a new 6 meter GI-46B prototype...I will post that here an a couple of weeks....After that I am building myself a new 160 meter shack amplifier...I currently run a water cooled single GS-35B on Topband...As I am getting up in years I have decided to revert back to air cooling...Old age, 4kv HT and water condensation on vinyl water hoses are not a good mixture, so time to take stock, make things safer and sit back happy....

Enjoy....Bob..VK3ZL..

[PA5COR]

As usual it is a beautifull set of piccies Bob, and a pleasure to see how much detail you put into the amps, i would have been closer i might have opted for one of yours in place of the Heathkit SB-1000 i rebuild.
Keep us fed with thse piccies, keeps us off the street and out of trouble ;)

[K7SGJ]

Damn, Bob. That is some more outstanding work. I never get tired of seeing your work.

Where do you get your tubes? And, what do the GI-7BT run down under? I wish I had the time and metal skills to put something together from scratch. Everything I ever did was using commercially available enclosures and adapting them. I could use one of my skills to make a nice enclosure, but I doubt oak would be a good choice.

[N1LAF]

Professional Schematic Generation in standby...

This is all I can get from the photos.

http://paulfelgate.com/hamisland/VK3ZL_AMP.jpg

[N8YX]

Looks good - as always! :cheers:

[KC2UGV]

Nothing I can add here... Just gorgeous.

[NQ6U]

Looks good - as always! :cheers:

Yeah, and will you please stop doing that? It makes the rest of us feel inferior.

[WA4TM]

Yeah, and will you please stop doing that? It makes the rest of us feel inferior.

I'll second that statement!!!!!!! I still have problems with static on FM broadcast radio!:lol:

Looking darn good Bob!!!

[K7SGJ]

Yeah, and will you please stop doing that? It makes the rest of us feel inferior.

To be honest, I feel inferior when I see someone that can color and stay inside the lines. I can't find the words to describe what I feel when I see Bob's work.

[VK3ZL]

Damn, Bob. That is some more outstanding work. I never get tired of seeing your work.

Where do you get your tubes? And, what do the GI-7BT run down under? I wish I had the time and metal skills to put something together from scratch. Everything I ever did was using commercially available enclosures and adapting them. I could use one of my skills to make a nice enclosure, but I doubt oak would be a good choice.

Gidday Ed and thanks all for the compliments...Well, this was a job for ME for a change and I have enjoyed the whole process..

I normally run pairs of GI-6 and 7 tubes to 800 watts output...This seems to be the happy spot for them...This amplifier will tune up to 1200 watts carrier with 55 watts of drive..However the tubes wouldn't stand that for long unless water cooled...I think I have mentioned in previous amplifier posts that I prefer to run tubes well under their full capability..

I buy all my GI-6 and 7B tubes from an Ukraine ebay source, RADIOKOMPONENT..Andy is honest, reliable and fairly priced..I also buy GS-31 and 35B tubes from Alex Gavva UR4LL...You can google his website with goodies for sale...These Cold War Russian tubes are very robust and I have yet to destroy one..My EME amps running JT65 for hours on end using GS-31 and 35B tubes on 6 and 2 meters are all still going strong...This is running 600 watts (GS-31B), and 800 watts (GS-35B) in data mode....Modest power but with big beams all that is needed..

Sorry if I get carried away with my replies, just put it down to senility...Bob..

VK3ZL..

[VK3ZL]

Professional Schematic Generation in standby...

This is all I can get from the photos.

http://paulfelgate.com/hamisland/VK3ZL_AMP.jpg

Havn't forgotten you Paul..Will get around to it soon...Bob..

[mw0uzo]

Looks soooo tasty, great work :D
Just love the simplicity of it. I know where to go for advice if I dare to build one!

[W3WN]

dayum

Man, I wish I had the time, the parts, the tools, and most importantly, your skills. I've seen commercial amps that didn't look that professional.

Great job. I'm envious.

[AE1PT]

Nice project Bob. Once upon a time, I knew many hams that built their gear from scratch--and I mean high caliber construction and design. You are keeping a great tradition alive, and doing a find job of it!

[VK3ZL]

Nice project Bob. Once upon a time, I knew many hams that built their gear from scratch--and I mean high caliber construction and design. You are keeping a great tradition alive, and doing a find job of it!

Thanks for the kind words Paul..I am always striving to improve my skills with each project..I am lucky to be blessed with heaps of time, patience and and a desire to do things right..I had many old hams, ( all now SK) who gave me their time encouragement to learn simple metalwork skills and a basic understanding of electronics and over the past 50 years I have never forgotten the advice "A job worth doing is a job done well"..Even in my old age I am still learning how to do things a little better every time I start something new...However if you check my storage shed you will find quite a few "dead marines", projects that didn't turn out right or didn't come up to my expectations..This happens to us all...:chin:

Bob..VK3ZL..

[koØm]

Yeah, and will you please stop doing that? It makes the rest of us feel inferior.

Yeah, times 10

.