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Steel tube driver for 3cx3000A7?

Discussion in 'General CB Services Discussion' started by 960, Aug 21, 2006.

  1. 960

    960 Member

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    What would be a good steel tube driver for the 3cx3000A7??

    It needs to DK up to atleast 700 Bird.

    1 4cx250b?
    2 4cx250b?
    4 4cx250b?

    1 4cx1000A?

    Another other ideas?



    Steel on steel is what my buddy is looking to do, no glass.

    Thanks for the suggestions.
     
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  2. Toll_Free

    Toll_Free Active Member

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    I wouldn't run any of those tubes that hard.

    1 4CX1000 has no grid dissipation... At least not enough.

    Get a 3CX1000. It's about the same as a 4-1000, but uses a complete steel structure. Uses 100 watts for > 1500 watts output, and only needs a couple thousand volts on the anode. No messy screen, either.

    It's also the smallest rebuildable tube they made... At least when I did this full time. 3cx1000 is the BEST driver tube EVER. It will take more abuse than an 8877, is rebuildable (get a 1200 rebuilt) and are available if you know where to look as pulls.

    Since they aren't as popular as the Sputtering 8877, you can find them cheaper, either.

    --Toll_Free
     
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  3. 960

    960 Member

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    Toll Free,

    what do you think you would get out of a a 3cx1000 with a 2watt deadkey swinging 20 Bird from a radio (or about 40pep watts). Will the 3cx1000 handle this?

    If so, I wonder there is a popular amp to use that doesnt have limiting and filtering and crap like the ameritrons for exaple (no offence to anyone who likes or run them).. Thanks
     
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  4. Toll_Free

    Toll_Free Active Member

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    Its been quite some time, but I believe not a whole lot. I seem to recal about a thousand / fifteen hundred for 100 watts or so drive (from my kenwood ts440.....). As I said, it's been years, but I don't think that 20 watts would get him more than a couple hundred out of that box..... Unless you went WAY over on the anode voltage.. I wouldn't, though.

    If he wants to do it from just his radio, he is going to need to do a tetrode, or a single pill as a driver. You could do a 2290 or 2879 into that 3CX1000, that would work... Otherwise, to go from 4 watts to the 500 to 3K people like to stuff those boxes with, hes gonna need a tetrode.

    4CX1000 or 1500 might do the job for him, but it would need input attenuation (funny, huh... Attenuation on your driver..)....

    I'd do a small driver, drivin the 1000 tube (3cx1000). 1 pill could be installed in the box, and it would only need to hit 100 watts... So it would be BARELY noticeable, and could actually work AS the tuned input....

    hrm.

    Anywho.
    --Toll_Free
     
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  5. scottdarling1221

    scottdarling1221 BANNED

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    You brainiacs forgot to ask how much plate voltage he has on the 3000.
    A 3000 with 4kv on the plate and 100 in will get a 2kw or more carrier.
    A 3000 with 6600 volts on the plate and 50 in will get a 2kw plus carrier out.
    Boy you guys need to learn.You could put even more on the plate i know guys running over 7kv on the plate.I have build boxes with 4kv and some with 6600 volts dc on the plate.
     
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  6. Shockwave

    Shockwave Sr. Member

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    I'm thinking 700 watts carrier or 2.8 KW PEP is too much drive on the 3CX3000 tube. If the box is put together right it will make over full rated power with far less drive. I used 400 watts carrier with 2 KW PEP drive on a 3CX6000A7 amp posted in the "tube amp pics" section. It produced 8 KW carrier and modulated 40 KW PEP. It would have done more if I used a vacuum tuner to replace the failing gamma matches.

    Toll free is right, only way to get from 4 watts to the drive level required for a 3CX3000 in one stage is to go tetrode. Good luck finding a well built tetrode amp for 11 meters with shunt screen regulation. If you want to make it simple and use a triode, the 4 watt radio is going to need replacing with something like a FT-101, FT-757 series, or one of them "turbo" 100 watt CB's for AM.

    Once you have 100 watts PEP drive from the radio on AM you can feed a single ceramic triode to drive the 3CX3000. The 3CX1000 would certainly run comfortably as a driver for the 3000 tube. Personally, if the goal was as few drive stages with low drive requirements, I would have built something like a 4CX5000 as a tetrode and hit it with a 100 watt radio. With all the MRI surplus tubes and Russian ones, combined with the "tetrode board" this is within the reach of a good amp builder.
     
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  7. Shockwave

    Shockwave Sr. Member

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    It is also worth commenting as Scott delicately points out that plate voltage does effect drive requirements to some extent. I was using 7 KV full load on the plate of the 6000 tube. That made my drive carrier requirements a little lower then normal. Plate voltage has a bigger impact on output power then drive requirements since a given tube needs to be operated within a certain window to obtain good efficiency without arcing. To make a long story short, higher plate voltages do much more in terms of output power then higher drive levels could ever do.

    The best maximum power output while still retaining good reliability on large Eimac ceramic tubes is about 20% higher plate voltage then published ratings. This extra plate voltage from a well built power supply makes a big difference in positive peaks (forward swing) on AM. Going more then this will risk internal tube arcs. The key to keeping good tube life at these voltages is not exceeding rated plate or grid current. The tube can handle 20% more voltage but higher plate current will cause too much cathode emission and lower the tube life. Higher grid dissipation will cause the grid to melt and short.

    The sad thing is too many 11 meter amp builders don't even know how to use ohms law to calculate plate load impedance and use this information with a resistor and SWR meter or antenna analyzer to match the tank circuit. So many times I've seen where "technicians" will make a tank coil and as long as it tunes up without the load or tune caps being at the ends, everything is good. That sure is a long way from making certain there is an efficient match between the tube anode and RF output connector.

    I can say Scott has learned how to build a good amplifier that runs stable, efficient, and reliable but my friend needs to not belittle others simply because they don't know as much as you. It took me many years to learn what I have once I figured out I didn't know it all. Do things the right way. Offer them the information and when they come back with the "I know it all" attitude then belittle them and call them brianiacs :)
     
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    Last edited: Mar 30, 2010
  8. scottdarling1221

    scottdarling1221 BANNED

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    your right i apologize if i came off like an ass las im sure i did.I have shockwave to thank for atleast 90 percent of the knowledge i have learned and the rest was from me having to figuring things out on my own but in some shape or form used knowledge i learned from him to get the awnser.

    Tetrodes are nice but take forever to make low drive no need for multiple drivers.Triodes are ok also as long as you build them right so you need as little drive as possible and are protected so they dont blowup if you make a mistake with the amount of drive you feed them or if you have it way out of tune.

    I my self am learning somthing new everyday no one knows everything.I am in the process of building a 160-10 meter box with a 3cx3000a7 with a 20 amp roller inductor.And i am finding out its not as easy as a mono band box thats fr sure and that i am limited big when it comes to power output due to the roller inductor.I would have used a 30 amp roller but it was way to big almost 16 inches long and 10 3/4 wide and 10 3/4 tall. So with the voltage i am going to run and a q of 12 i am limited to around 1.6 amps of plate current which equals around 1.4 kw and 4 times that peak.

    If i went with a 6000 tube i can increase the plate voltage and then i can get a little more power.I could even leave the 10000 in it and raise the plate voltage to 10kv.I have a bunch of 6000 tubes and 1 10000 tube all good.

    Ofcourse i will observe the legal limits this box is being built with over kill inmind since i talk on am on the ham bands.
     
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  9. Duppy Conquerer

    Duppy Conquerer Member

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    Very humbling....like the fact that scotty stepped up and appreciated the critique. I am new here fellas and would like alittle assistance. I posted in the amplifier section...would appreciate some help.
     
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  10. vo1ks

    vo1ks Active Member

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    The 8874 is used as a driver for the 3CX3000A7 in FM broadcast transmitters. Both tubes operate grounded grid. About 10 watts drive is capable of producing over 5kW output power 24/7. I don't have plate volt or current specs off the top of my head...
     
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