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HF homebrew tube amp photo build

Discussion in 'Home Brew' started by Radio Tech, Sep 30, 2009.

  1. Radio Tech

    Radio Tech Radio Operator

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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.
    [​IMG]
    [​IMG]

    [​IMG]

    [​IMG]




    You can tell by the size of the watt meter how big the case is
    [​IMG]
     
    #1 Radio Tech, Sep 30, 2009
    Last edited: Oct 20, 2009

  2. MisterFatty

    MisterFatty Poppin Fresh!

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    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.
     
  3. Radio Tech

    Radio Tech Radio Operator

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    In the begining

    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.:LOL:
    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
     
  4. Radio Tech

    Radio Tech Radio Operator

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    Safety

    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:eek:

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

    Captain Kilowatt Professional Amateur
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    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 .:headbang 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. :cry:
     
  6. Radio Tech

    Radio Tech Radio Operator

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    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
     
  7. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    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.
     
  8. Radio Tech

    Radio Tech Radio Operator

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    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 Files:

  9. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    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.
     
  10. Radio Tech

    Radio Tech Radio Operator

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

    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.
     
  11. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    I thought I would move this thread to the Home Brew section and make it sticky so it will be easier to follow the progress. I will also start my own and drop some pix as time goes by. (y)
     
  12. Radio Tech

    Radio Tech Radio Operator

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    Sounds great!
    Did not get off work until late today. In fact just got home 30 minutes ago. Had to cover for someone. So probably want get nothing done here.

    QRN do you have a 572B handy? If so measure from the top to the tube base so I can see if I have the clearance I need when so if I switch to that tube. I do not have one at the moment.
     
  13. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Sorry no 572B's on hand, just some 811A's. Check this link out for the original specs of the 572B,both physical and electrical specs.

    http://www.r-type.org/pdfs/572b.pdf
     
  14. linearone

    linearone King of NY

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    Russian tubes.

    I like em. They are cheap (we will come back to this), has reasonable filament demands and make good power.

    Downsides:

    1) These tubes are RUSSIAN SURPLUS. You need to understand that when the surplus dries up, thats it. The price will go through the roof, no one will rebuild them and you will be left with an amp that is about as useful as a 12 tube Phantom with 6lQ6's. These are the cheap and plentiful sweep tubes of today. If someone was to do a 35b box I would buy all my spares now while I could and sit on them. I have already seen the price tag jump over the last 4 years. First they were $85, now they are like $120 or so last time I looked.

    2) They are not a zero bias triode and require quite a bit of biasing to prevent them from running wild and drawing too much current at idle. they can draw almost .4 amp each at idle in grounded grid with no bias applied.
    in contrast a 3cx3000a7 will draw anywhere from .230-.4 at idle BUT has a mush higher total output and plate dissipation.

    3) All the data sheets I have seen for the 35b tend to have different info. , all different values etc etc. this bothers me. I think this is why when testing these tubes I find one can draw a considerable amount more current than the one next to it(filament)

    4) only one guy makes a socket and chimney and its expensive. I have seen some good homebrew solutions though.
     
  15. Radio Tech

    Radio Tech Radio Operator

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    Thanks for the Russian tube info linearone.
    I myself have not done much with them but have been doing a lot of reading up. I do have a couple I am going to do a tube swap in a MLA 2500. Just waiting to get rest of the parts.

    Thanks for the link QRN. That was helpful.

    This morning I finished tearing the chassis down and got it all sanded. Next is to get the RF deck fabricated. The tube compartment will drop 1 inch lower than the top of the chassis. This way I can make a full enclosure for the tube compartment and have good shielding. I also will blow air up and across the tubes. This way we should be able to get the heat out of the box instead of blowing across other components.

    More to come.
     

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