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.

[N8YX]

Looks good - as always!

[KC2UGV]

Nothing I can add here... Just gorgeous.

[NQ6U]

Looks good - as always!

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!

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.