Need help with Homebrew linear toob selection

[N9NEO]

Holiday Greetings.

I intend to build a linear over the next year and need some advice on tubes.

I have  10watts of drive from a HX-50 and am  interested in 160m-80m-40m only.  I realize HX-50 is not a very good  performer, but I will dial it in ok so it sounds good.

I am looking at 2 ways of skinning this cat.  Mybe a 6146 driving into a pair of tubes, or one maybe 4CX800A tetrode tube.

A pair of 572B tubes are about 100 bucks and the 4CX800A tube is about $140.  These prices are from Tom's tubes and I'm fairly certain they are from Russia.

Are these reasonable ways to go?  One better than the other?  What should I expect for output power.  Are 811 or 813 tubes another possibility?

best regards,
Bob
N9NEO

[Glenn NY4NC]

Hi Bob;

How about a single 3-500Z grounded grid?.. Inexpensive tube, readily available, easy to build, don't need a leaf blower to cool it, good IMD, stable...

I've been using a single 3-500Z for several years now for amplifying my AM exciter. 10 watts of drive gets me about 125 watts out. I would have gone with a pair of 3-500Z's but I couldn't get 220v in the shack in my last house. Not the case with the new QTH 
 

Holiday Greetings.

I intend to build a linear over the next year and need some advice on tubes.

I have  10watts of drive from a HX-50 and am  interested in 160m-80m-40m only.  I realize HX-50 is not a very good  performer, but I will dial it in ok so it sounds good.

I am looking at 2 ways of skinning this cat.  Mybe a 6146 driving into a pair of tubes, or one maybe 4CX800A tetrode tube.

A pair of 572B tubes are about 100 bucks and the 4CX800A tube is about $140.  These prices are from Tom's tubes and I'm fairly certain they are from Russia.

Are these reasonable ways to go?  One better than the other?  What should I expect for output power.  Are 811 or 813 tubes another possibility?

best regards,
Bob
N9NEO

[Glenn NY4NC]

Another great tube/option I forgot to mention in my last post is the Russian GS-35B triode. You can get them new for $79 plus shipping from the "QRO-Stuff Store" You'll get 2kw+ in a grounded grid configuration with around 3kv on the anode. Don't need a socket, they can be mounted directly on your chassis. Best dollars-per-watt choice.

Here's a link to the E-bay store that sells them;

http://cgi.ebay.com/Tube-GS-35B-new-in-box-2500-W_W0QQitemZ5841508470QQcategoryZ48710QQtcZphotoQQcmdZViewItem

And lots of info on building an amplifier here = http://amp.w4zt.com/

...and here = http://home.comcast.net/%7Ewb8wju/

[K1JJ]

Hola Bob,

Lots of ways to go.

You being a very technical guy, this may interest you. I've been getting a good edumacation from the Amps Reflector about using tetrodes with negative feedback. Normally a GG amplifier is good for -32 to -36db 3rd order IMD according to the amp manufacturers in the real world.

But by using drivers that are running in class A, low level and driving a tetrode with voltage only, you can achieve upwards of 50db+ 3rd order with the drivers.  Then put some RF negative feedback around the tetrode power final to bring it up with the rest of the chain.

I like this design and plan to try it out. Read my post about IMD tests and you will see the difference it makes when tuning across a signal going from a -32 signal to a  to -55db 3rd order signal. [Estimates]
 
This applies to both AM and ssb, of course. With input baseband frequencies out to 6kc on AM, a little IMD can really raise havoc compared to the narrow <2.8 ssb audio.

Starting with only 5 mW into a OPA695 op amp at 500mw, I plan to use a 6550 running class A putting out LESS than a watt, driving a 4CX-350 running class A also putting out a watt or so [mostly for voltage] driving a 4CX-3000 with about 20db of negative feedback from the 4X3 back to the 4CX-350A.

We'll see.

A 6550 driving your  grid driven 4CX-800 with neg feedback could be a nice, clean way to go. No grid current in the 4CX-800 - Running 350V on plate, 200V on screen and -37V on grid of the 6550 gives deep super clean class A operation with enough voltage swing to drive the 4CX-800 easily.


BTW, check out your 10W IMD output from the HX-50 first. You want that to be at least 10db cleaner than the amplifier to make sense here. You may be able to do this with some serious work.

Here's a schematic using a 4X10 and a similar scheme. Notice the ease of the neutralization and the negative feedback. Simple.  You can scale this for many types of tetrodes.  ALL of my amps here are triodes, and I feel they could be cleaner, thus the effort.

Copy and paste this into your browser and go - it does not work by clicking on it as a direct link for some reason:

http://wc6w.50webs.com/wc6wamps/popp.html?h10a1.jpg


Just another approach to consider, OM.

73,

T

[W2VW]

The answer depends on what you have available for a power supply. No matter what:
572b's are overpriced for what you get.
For AM the name of the game is plate dissipation.
6146's should be declared unconstitutional.

[WA1GFZ]

Bob,
There are many possible ways to skin the cat. The all time cheapest way to go is use 813s. This may be a safe way to learn. Being a smart guy I'm sure you could easily build something bigger. Just start collecting parts. and see where it takes you.
The Russian tubes sure have become popular.

[Glenn NY4NC]

No way dude!.. Isn't Irb using them in his dixie 100?? 

6146's should be declared unconstitutional.

[W2VW]

No way dude!.. Isn't Irb using them in his dixie 100?? 

6146's should be declared unconstitutional.

Exactly. YOU are suppposed to do as Irwin says not what Irwin does.

[N9NEO]

Ok, then it's settled

73
NEO

[K1MVP]

Ok, then it's settled

73
NEO

Bob,--N9NEO,
    I have some "info" and skizmatics on grounded grid 813 amplifiers, which I
     have collected as I am in the process of just starting to build an 813 amp
     for 160, 75 and 40.
     Let me know if you would like/ or need info, and will get try es get some
     of it together and I can snail mail it to you.

                                    73, Rene, K1MVP
 
 P.S.,With a pair of 813`s, u should be able to get at least 150 watts out es
       while its not 300, you will still be only 3 db down from running 300 watts,
       and the 813`s are "dirt cheap" and thus you will get a lot of "bang for
       the buck".

 P.P.S, I think a Valiant with three 6146`s will give you 150 watts, so you would
          be on a par with a Junkston Valiant, --not too shabby, and you could
          run an exciter with "good quality" audio into it .     

[W2VW]

Tetrodes are a major pain in the backside. You have to work around screen bypass capacitors which must be low inductance and usually expensive. A 4CX800 either needs to run in grounded screen or have a relatively expensive screen bypass capacitor built into the socket. Then you have to have a solid screen supply that can sink negative screen current. Then you should have glitch protection like gas discharge devices so your complicated screen supply doesn't blow up WHEN the tube arcs internally. THEN the distortion will probably not be too good unless the tube is cathode driven or grid driven with degenerative feedback using some resistance introduced into the cathode.
Any tube(s) cornsidered for a new linear amp design should be priced including the proper socket chimney and blowers if used.
Then take the whole thing as dollars verses plate dissipation. If you really like the tetrodes then try a GU-84 or a GU-78B.
http://www.nd2x.net/tube-1.html
The trick is to find the sockets with a built-in screen bypass. Screen bypass rings can be fabricated at home using Beryllium Copper finger stock purchased from Surplus Snails and mulitple "chip" capacitors.
The olde standby best kept secret would be 813's. Triode connect 4 of them and you will have a great low band only amp. Parts count will be up with this and you might want extra toobs on hand in case some aren't up to the standards of the others in parallel.
A single 4-1000 is nice too. Cathode drive it and if your plate supply isn't enough to get 1500 Watts P.E.P. out then put some negative bias on the control grid and a little
positive on the screen. You get the glass with the Orange glow and all the lead inductance problems that are married to glass toobs at the same time.
If none of the above posts including this one help then you could roll dice. Maybe a fortune teller......
A single GS-35B is nice but don't forget a socket fixture and chimney for the $ figure.
10 Watts will not drive one of these to it's potential. You will also want a B+ around 3500 Volts under load.

[Steve - WB3HUZ]

813s make nice zero-bias triodes when the screen and grid are grounded.

[KL7OF]

for more power, its easy to go to 3 or 4 or 5 or more... 813's ...........I always wanted to build one that has a row of 813's so I could just plug in more tubes for more strap..... 

[K1JJ]

for more power, its easy to go to 3 or 4 or 5 or more... 813's ...........I always wanted to build one that has a row of 813's so I could just plug in more tubes for more strap..... 

Yeah, that would be fun.  It's called a "barefoot linear", cuz you don't need a blower and it runs silent. You can tell 'em you're barefoot...

I know a ham who collected twelve 813's with sockets to do just that. Intended it for 160 and 75M. He never did and sold them off.

Then there's my buddy who put four in a linear with 4KV - got out 2KW pep.

So, twelve would be good for 6 kW pep, multiplied out.

Great tube, those 813's.

T

[WA1GFZ]

output C is a bit high for 20 and above but GG with a pair would do good power 4 should do 2 kw in. Lots of emission. i have a box full that I want to use some day. fc

[W2VW]

I have an old (4) 813 deck that belonged to a friend. The thing made every bit as much power as a pair of 3-500Z's for years. Once in a while He would replace a toob.
Don't let the 125 Watt plate dissipation rating fool ya. It's got the same sized plate as higher rated toobs.

4 with air on them is good for legal limit. Make it 5 to be different.

[Glenn NY4NC]

Can you still buy a new 813??..... If you use 4, don't you have to match them do a certain degree??
push-pull, parallel?
If not, one's gonna be huffin and puffin!!!

[Glenn NY4NC]

You don't need a socket.....and nothing wrong with a cheap PVC chimney..

That's right, 10 watts won't drive it to 2.5kw... but you can't run 2.5kw on AM, right??

A single GS-35B is nice but don't forget a socket fixture and chimney for the $ figure.
10 Watts will not drive one of these to it's potential. You will also want a B+ around 3500 Volts under load.

[Steve - WB3HUZ]

Matching is not really needed, unless one is really dead.

You can run 2.5 kW on AM. You can run as much input as you want. It's the output the FCC measures.

[W2VW]

1500 Watt carrier, 100,000 Watt upper sideband, 100,000 Watt lower sideband exactly 180 degrees out of polarity with the other sideband. Conforms to current part 97 regulations.

[Glenn NY4NC]

:

[Glenn NY4NC]

I thought we were talking about outpoot....

Matching is not really needed, unless one is really dead.

You can run 2.5 kW on AM. You can run as much input as you want. It's the output the FCC measures.

[W2VW]

A few months back I checked a large quantity of 813's. All were at least 40 years old and some over 60. They were HiMu triode connected as modulators during the test. I checked idling current and ability to make positive peaks. Some of the toobs had been pretty beaten. I found that pairing them is not really too difficult. Even different brands work together.

[Steve - WB3HUZ]

I suppose if we were really worried about wasting electricity, we wouldn't be on the air at all, or even have our receivers powered.

[W2VW]

I suppose if we were really worried about wasting electricity, we wouldn't be on the air at all, or even have our receivers powered.

In the words of the late W2WME:

All non-essential communication is just that, non-essential.