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Been digging through info for about 6 months now.

Next project, HF all band amplifier.
Took me a while to decide on what tube to use. So going to use the 811a since a have a shelf full of them. Now to decide on how many to use. Seems 4 was the magic number but maybe more. Have to do the math.

I got this huge black ugly case I need to do something with.

Pics to follow as this comes along.

May be requesting folks to check their junk boxes!

Below is the chassis I am going to use. For the last 20 years it has been a power supply ranging from 5 to 800 volts. Time to give it a new face and use it for something more usful. It this case, an HF Amplifier.
It is a rather large enough chassis to handle the project.








You can tell by the size of the watt meter how big the case is

Always love these threads, it is great seeing what an individual comes up with, only so much you can do with 811's but seeing it come together as a package is cool as hell....

I was considering a similar project, just because its been a while, but now I'm kind of thinking about a GS35b Project.

May I ask your experience level, and how much you've already done with Tubes?

My 811 project was going to be planned with a 4 tube final build, and stops at each tube addition, document the build along the way and end up with a multi level project which would be fairly versatile. then perhaps, down the road a bit, change over to 572Bs as $$$ permitted. Ambitious but fun.

Needless to say I've been intrigued by the Russian surplus so the project will probably never go anywhere.

I agree, a lot can be learned from threads such as these. Sort of why I like to stir the pot so to speak. Projects are always good.

Oh boy. Scared someone would ask that.
I started building tube stuff when I was in my teens (14). Been doing it ever since. 90 percent of my business here at the shop is tube. I work on and restore older tube radio and amplifiers. Just finished up a Heath kit SB-220 and 2 LK-800's. Work on tons of Tram and Browning rigs. I just love the old stuff.

I have a AB Standard Radio Receiver in the shop at this moment. This was made in Sweden many years ago.

As far as your project the Russian tubes are the way to go now. Should be a fun build. I have a MLA 2500 in for a tube swap. C-36b's

I do want to say this.
The first thing you need to know about building or working on any amplifier is safety.
Guess what? These amplifiers wil not hurt you. THEY WILL KILL YOU!!!!
These voltages are very lethal. And are the cause of SK every year other than falling off towers.
Please be careful with any project such as this.

I work on quite a bit HF amplifiers and thank God that I have never been hurt.
In just the last month I have repaired the following
Heath SB-220
Heath SB-221
Drake L4B
Amp Internatinal LK800
Amp Internatinal LK800 NTC

The last two have 3500 volts on the plates

Now we will be working with much less than that with this project. But still dangerous.
Never test alone.

I will be follow your progress as well. I was going to build a BIG amp with four 3-500Z's or 4-400's, and still plan to do so but not for another year or two anyway. I have decided first to build a four tube amp using 572B's. I was going to use the lovable 811A but found I could make a nice stiff 2000 volt supply which is a little too much for the 811A's and I want (need) higher plate dissapation to run AM. I just cleaned up a cabinet yesterday for this and found out that my loading cap is too long to fit in it . Before I order the 572B's I need to address an antenna issue here which may result in the purchase of a Butternut HF9V to get me going back on the air until I can put up a new tower and build a quad. Too many projects and too little time and money.

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Front/back ratio comes from the antenna. Forward gain comes from the wall socket.

Kewl!
Chime on in anytime.
The 811a are good tubes and are readly available at decent prices.
The downfall to the 811a is 6 meters. Forget it. The cathode is too small.
But the 572b works great on 6 and this amp can be used with either.

4 3-500 is a lot of heat! But would be a sweet amplifier. If I was to build that I would follw the Drake design.

I know what you mean about time and money. I am tight with both.
But I need a new amplifier since I sold my comercial units and been wanting to start an amplifier project.
A simular tube is the 572b

I may use just a pair but a quad is still a definate possibility. I want to be able to run AM with my Canadian legal limit 750 watt carrier modulated to 100% and not worry about blowing a tube. I have the parts from an RCA 1Kw broadcast transmitter to get me started. It used 4-400's so I even have the sockets and chimnys as well as the vent stacks since 4-400's and 3-500's use the same sockets. BTW,yes the chimneys I have WILL fit the 3-500's.

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Front/back ratio comes from the antenna. Forward gain comes from the wall socket.

I think the 4-400 is a zero bias tube? But the 3-500 requires bias. Higher for AM and lower for ssb.
Also when cathode driven you will need a tuned input for the 3-500.
The good thing about the 4-400 is it is not required since the input impedance will be at 50 ohms.

Oh yeah.
Big tube chimney!

Attached Images

d087_2.jpg (3.8 KB, 14 views)

Actually the 3-500Z is the zero bias tube while the 4-400 being a tetrode likes to see some screen voltage applied.They can be run as a triode in GG service and that is what I will do if I run them.I'll probably construct the amp using the 4-400's and after it is running convert to 3-500's. No sence risking new tubes.Anyway I'll have lots of time to plan that one as it is on the back burner for now. The 572B amp will come first.

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Front/back ratio comes from the antenna. Forward gain comes from the wall socket.

Thanks for that clarification! I had it back wards. I really need to be posting from in the shop with my notes in hand.

Since I have a bunch of 811A's that is what I will do on this project. Then maybe later switch to the 572b's. Although I do not think the price is bad at the moment

This week I am going to sand the chassis down and weld in a new piece of sheet metal since this one is full of holes. At the moment the tubes will fit with 1 inch of clearance from the top flip door. I plan to drop the tube deck about another inch into the lower chassis. I will also sheild the tube deck and use forced air for cooling.

The front panel I think will work out with out much modifications. As you can see in the pic there are 4 big volt anf mili amp meters. Along with 2 switches and two lights.

I already have a band switch and tank coils. A bunch of parts from a Pride 300 and some from SB-200's

Can not wait to see this come together.