A New 6 meter amplifier project..

Hi all....It has been a while since I posted one of my amplifier projects...I decided to up the power stakes in a new amplifier for 6 meters and put this unit together using a Russian GS-35B 1500 watt anode dissipation triode...I have experience using these tubes in my water cooled 160 meter amplifier and have found the Russian triode an exceptionally rugged and reliable generating device...

My first job was to source a suitable HT transformer compatible with the tube....I ended up ordering a custom made hefty Toroidal unit with multiple secondary taps for flexibility so that it can be used with other tubes...The pictured transformer was the result and after testing I ordered a bulk lot for future projects..

The actual amplifier project was straight forward using my past experience setting things out so that servicing is easy....The amplifier has a hinged front panel allowing access to the control circuits, step start and bias circuits etc...

The RF deck contains the tube, plate choke and a Pi L output circuit....I used a new Jennings 1-10pf vacuum variable 25kv neutralising capacitor for plate tune, a 1/4 inch silver plated inductor and a new 200pf German kit capacitor for loading....The L coil is a 5 turn 10 gauge inductor....The amplifier uses a hefty Russian coaxial relay for output...

The input is simple consisting of a Tunable T network...The filament tranny is Toroidal, multi tapped primary so that I can set the heater voltage to 12.6 volts..

The serious stuff is in the HT power supply of course....The rectifier consists of 22 6A10 1kv 6 amp diodes and 10 470mfd 450 volt electrolytic capacitors...I used the 1425vac tap on the HT transformer to give me around 3700vdc.....Now this is serious stuff to have on your desktop and if it catches fire don't pee on it...That will hurt...Keep the kids away from it also..

The amplifier cooling is done with a large heavy 6 inch Papst 7450ES Metal Bladed fan...The RF deck is pressurised the air being drawn in through the HT PSU..The air exits through the tube cooler and Teflon Chimney on the top cover....Air pressure shows .4 inch on my manometer, more than satisfactory..The cathode compartment is sealed from the RF deck and is cooled by a smaller aux fan..

I used all anodised aluminum for the amplifier case....I carefully ground away all surfaces at the joins where the surfaces came together...The case came together beautifully and looks very nice and is completely RF tight..All earthing points were cleaned both sides to make sure of good contact...

I finally finished the project last week and tested all electrical functions ensuring everything worked as designed...It was time to apply a bit of RF and see what happens....I set the amplifier up with two Bird watt meters and a Bird 1kw dummy load and connected up the Yaesu 897....First job was to run 10 watts in and set the input T network to 1-1 vswr...Then I proceeded to tune and load the amplifier in increments...Everything went beautifully and the final outcome was better than expected....Something to note using these triodes, the input needs to be finely tuned as you increase power to get the most efficient transfer of power and grid current...I gave the amplifier a few days of hard running using CW fast dots at 1kw output...30 minutes on and 5 off....It has never missed a beat and power output doesn't vary....The poor Bird dummy load doesn't like it though and started to protest eventually..

The final figures were 1600 watts carrier output with 95 watts of drive....The amplifier "sweet spot" is 1200 watts with 60 watts drive....The efficiency starts to drop away at higher power mainly due to the HT transformer limit..

I designed this amplifier as a 1kw output unit to suit the new 1kw power limit being introduced in March this year....I think I have achieved all I set out to do...

Messing around with this stuff is fun and sometimes terrifying if the XYL walks into the workshop and says BOO....Being a cantankerous old fart and at my age only having a short attention span I often wonder how I havn't electroplated myself..(:-> However I love doing these jobs and I am already building Mk2 of this amplifier and another 2 meter version...

Enjoy the pics....Bob..VK3ZL..

A few more pics..Behind front panel showing the simple step start and bias setup.


Bob..VK3ZL..

well done

Excllent work Bob, a pleasure to the eye ;)

I stick to the 200 watt here from my Yaesu FT 2000 D, our limit is 400 watt anyway, so for the 3 dB extra i won't make that effort.

Hotchie Momma!
You always do beautiful work! And look! No shipper's footprints!

Bob, you are a true artist. Nice work.

What the barkeep said.

Very nice!

Impressive work. Have you built anything similar for the 144, 222 and 432MHz bands?

Beautiful work, Bob—as usual. I have to hand it to you: it takes some cojones to work with that kind of voltage. Just dealing with the comparatively wimpy 700V in my T-4X scares the crap outta me.

Every time I see your projects, they simply amaze me.

Amazing workmanship, you are a true talent.:clap:

I'm a little inexperienced in this hobby to totally appreciate the electronics portion of what you accomplished. However, I can very much appreciate the metal work in the cabinet. You said you have a shop. Does it include a metal bending brake? That case is beautifully straight and square :) If I'd tried to do that by hand, I guess it would end up a trapezoid and have lots of RF leaks. :doh:

Thanks for all the nice encouraging comments...I do build 2 meter amplifiers and the odd 70cm on request ...70cm is a lot harder to get efficiency...

I have a simple workshop and no special tools...I do everything by hand...I actually order the sheet metal cut to size for the amplifier cases...I use aluminum angle and pop rivets to do the final assembly..The cases take around a day and a half to complete as I have to cut out all the holes fror meters, sockets etc by hand...As I have been doing this for many years the job is routine to me...Fitting everything perfectly takes time and practice..Mum knowledge of electronics is rudimentry but I have taught myself through experience...Solid state leaves me cold..

Bob..VK3ZL...

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Originally Posted by VK3ZL

Thanks for all the nice encouraging comments...I do build 2 meter amplifiers and the odd 70cm on request ...70cm is a lot harder to get efficiency...

I have a simple workshop and no special tools...I do everything by hand...I actually order the sheet metal cut to size for the amplifier cases...I use aluminum angle and pop rivets to do the final assembly..The cases take around a day and a half to complete as I have to cut out all the holes fror meters, sockets etc by hand...As I have been doing this for many years the job is routine to me...Fitting everything perfectly takes time and practice..Mum knowledge of electronics is rudimentry but I have taught myself through experience...Solid state leaves me cold..

Bob..VK3ZL...

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Lol, rudimentary. Talented and modest.

Well, that amplifier just sold for $1800...That's $1k for all my work and time..I'm happy..
I have another 2 meter unit completed and ready to sell next week...Ya know, keeps this old geezer outta the pub...
I have already started another 6 meter GS-35B amplifier so I will be busy for another couple of weeks then I will have to find something else to keep myself occupied...Retired since 1983 and I don't know where the years have gone....Ah well !!! :dunno:

Bob..VK3ZL..

How many hours did it take to build the 6M amp?

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Originally Posted by K7SGJ

How many hours did it take to build the 6M amp?

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Probably 25-30 hours all up....

Bob..VK3ZL..

Simply amazing! and beautiful work.
I love to build something that takes 10 watts in and a couple out.
Schematics are hard to find

I have built 2 GS-35b amps and, I have a third one that I have taken a sabbatical on building until things slow down around here. The first was a single tube / single band model. 4500 on the plate Ip was about 1.0 amps with 100 peak watts of drive produced upwards of 3000 watts on the Bird 43P. Second one was a 2 holer with 5000 on the plates that did over six easy. They worked great, but compared to your construction, I am humble, embarrased and not qualified to sweep the shaving from your shop floor.

I see that you are using the W4ZT bias type board, what the idle current one the tubes during zero-signal mode and, what the Ip and Ig under transmit?

Attachment 5405

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Looks pretty nice to me, Melvin. I like the vacuum caps.

[QUOTE=koØm;408896]I have built 2 GS-35b amps and, I have a third one that I have taken a sabbatical on building until things slow down around here. The first was a single tube / single band model. 4500 on the plate Ip was about 1.0 amps with 100 peak watts of drive produced upwards of 3000 watts on the Bird 43P. Second one was a 2 holer with 5000 on the plates that did over six easy. They worked great, but compared to your construction, I am humble, embarrased and not qualified to sweep the shaving from your shop floor.

I see that you are using the W4ZT bias type board, what the idle current one the tubes during zero-signal mode and, what the Ip and Ig under transmit?

.[/QUOTE}
G'day Melvin, you are doing ok I would say...I idle my GS-35B around 150ma....Grid current loaded at 1kw is around 200ma and 1500 watts about 300ma...I don't put more than 3700 volts on the tubes as I sell these amplifiers to hams, experience unknown....I do find that individual tubes show different characteristics as far as grid current and general performance is concerned....Grid current really isn't an issue and I know many hams using these tubes don't bother putting in a grid meter..Overall I find the GS-35B a very rugged tube and you would have to do something really stupid to hurt one at ham power...The 8877 pales against these tubes with it's delicate grid structure and looking at the $ value most Russian tubes are excellent value...:cool2:

73...Bob..VK3ZL..




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Originally Posted by koØm

I have built 2 GS-35b amps and, I have a third one that I have taken a sabbatical on building until things slow down around here. The first was a single tube / single band model. 4500 on the plate Ip was about 1.0 amps with 100 peak watts of drive produced upwards of 3000 watts on the Bird 43P. Second one was a 2 holer with 5000 on the plates that did over six easy. They worked great, but compared to your construction, I am humble, embarrased and not qualified to sweep the shaving from your shop floor.

I see that you are using the W4ZT bias type board, what the idle current one the tubes during zero-signal mode and, what the Ip and Ig under transmit?

Attachment 5405

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Nothing wrong with that construction. I would say you are MORE than qualified to do Bob's floor. Hell, with all the $$ his making on his amps, he'll probably fly you to OZ on his nickel (or it's equivalent in Aussie currency) just to do it.

Both you guys do really nice work!
I've been toying with the idea of one of these myself. I've got a TenTec 425, uses a pair of 3CX800-A7's, and the tubes are getting pretty soft. I'm having a real hard time justifying the tube replacement cost on this one. Eimac tubes are about $1600/pair, and Chinese tubes are about $900/pair. On the used market, the entire amp is in the $1500 range with good tubes.

Anybody care to do some close collaboration on a conversion?

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Originally Posted by W5GA

Both you guys do really nice work!
I've been toying with the idea of one of these myself. I've got a TenTec 425, uses a pair of 3CX800-A7's, and the tubes are getting pretty soft. I'm having a real hard time justifying the tube replacement cost on this one. Eimac tubes are about $1600/pair, and Chinese tubes are about $900/pair. On the used market, the entire amp is in the $1500 range with good tubes.

Anybody care to do some close collaboration on a conversion?

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G'day Doug....If you are considering a conversion check out the UR4LL website for possible substitute tubes...From my experience, Russian tubes are generally tough, reliable and cheap...There are a couple of Russian triodes that you may be able to utilise...You would probably have to do a part re build of the RF deck and substitute the filament transformer...Some commercial linears lend themselves to conversion than others however...You would best Google around and look at work other hams have done...Start with the W4ZT site...There are also many Youtube videos to be found....

Good luck..Bob..VK3ZL..