1. You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
    Dismiss Notice
Dismiss Notice
This forum does not allow a single user to have more than one username. If anyone wants to change their username contact an admin and it will be done. Multiple accounts belonging to the same member will be deleted without warning.

Ebay LDMOS amplifiers

Discussion in 'Amplifiers' started by TIN_CAN, Jul 28, 2020.

  1. TIN_CAN

    TIN_CAN Well-Known Member

    Joined:
    Nov 23, 2011
    Messages:
    277
    Likes Received:
    243
    Just wondering if anyone else have seen these things on ebay, the guy is offering 3 different amps 1000w 1500w and 3000wRMS all running blf188xr these would be fun to try out, prices dont seem too bad, then again how is the quality.

    https://www.ebay.com/itm/3000-watts...409020?hash=item3b4b00b8fc:g:Vh0AAOSw0D5fF3uN




     
    Handy Andy likes this.

  2. Shockwave

    Shockwave Sr. Member

    Joined:
    Sep 19, 2009
    Messages:
    3,196
    Likes Received:
    1,947
    This almost looks like an exact copy of the one "RF Man" was demonstrating on YouTube a few months back. Like most built before it using these 50 volt pallets, they work great when properly driven. Over drive it with just one watt too many and you'll have instant failure placing about $1,000 worth of transistors at risk. If you're going to go this route with no protection, the only way to achieve some reliability is to select an input attenuator that will make any type of over drive condition, completely impossible to achieve with the rig exciting it. Unfortunately, that also reduces maximum output power.

    By the way, the knob marked "gain" is not a gain control. If it were a gain control it could be set in any position without a change in signal quality, other than strength. It's a bias control that should be used to control class of operation and not the gain of the amplifier since doing so, will introduce distortion. The power being measured at the same level for peak and "RMS" is also not so accurate. What he's using as an "RMS" rating is really a flat out CW rating since there is no capacity to modulate and peak anything above that point, like would be required with an "average power rating".
     
    #2 Shockwave, Jul 28, 2020
    Last edited: Jul 28, 2020
  3. TIN_CAN

    TIN_CAN Well-Known Member

    Joined:
    Nov 23, 2011
    Messages:
    277
    Likes Received:
    243
    Thanks for the info on these, was looking for something different then the 2879 pill boxes which I will probably just stick with for now.
     
  4. nomadradio

    nomadradio Analog Retentive

    Joined:
    Apr 3, 2005
    Messages:
    3,569
    Likes Received:
    4,005
    Not one pic of the inside. For two grand-plus I would need to see inside the thing.

    73
     
  5. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

    Joined:
    Apr 23, 2018
    Messages:
    3,280
    Likes Received:
    3,607
    Because of the pellet size and mounting - not exactly a drop in, but to place scale on this, the older Pill (Read Bipolar) and its' "conjugate" needs of "interface layer" from the outsides' RF dynamics and power levels - the "Waveguide" approach is still used. So the Bias is now changed from Current thru a simple diode as a "Fix it all" is now Voltage-regulation based - and if any feedback is needed - Thermal to help with the transition.
    upload_2020-8-3_11-45-31.png

    Everyone thinks 50Volts is the new Baseline - well - they said similar with Tube designs back in the 30's and right on up to the Day they stopped making Hybrid design radios' like the T-240D - found it easier, and safer, to run single ended supplies - so can't really say the 50 Volts is a necessary requirement.
    upload_2020-8-3_11-49-40.png
    Just remember you're dealing with charts using a much higher frequency range spectrum.
    Gain INCREASES when you use lower Frequencies...
    Refer to Maximum Useable Frequency or
    HFE as your transition gain factor.​

    But if you have access to that voltage, you can use it with Envelope Tracking designs as your ability to "boost" your power envelope from your standard fare regulation (AM or Modulation) - just be careful with the outputs for small trickle currents at those voltages placed on the right parts of the body can cause Arrhythmia.

    It's not that hard to transpose what was done with Tube and Solid State - they did it before.

    You just have to reengineer the design to obtain the higher voltage - if that is a necessary requirement for you.

    But if you own a Tesla or Prius, well, let us know how it goes. Be sure to carry a Parachute, for the batteries in those vehicles do emit gasses that is not vented quickly enough, can cause injury and some considerable concussions if you don't have a sunroof or upper exit strategy in place.

    Our current (SIC) dilemma is limits, as well as the supply, not the voltage breakdowns. Heck the MOSFET is made rugged due to this. Bipolar has the voltage constraint (Direction Junction) Reverse breakdown issues. MOSFETs' give you that extra layer of protection like Cottonelle provides their fans - we're just now getting back into the fun part.
     
    #5 Handy Andy, Aug 3, 2020 at 4:37 PM
    Last edited: Aug 3, 2020 at 4:58 PM
  6. Trailblazer

    Trailblazer New Member

    Joined:
    Jul 23, 2020
    Messages:
    1
    Likes Received:
    2
    Hello all,
    Believe me when I say I dont have a dog in this fight. I did however come across in my wanderings info and sales of this palette design which piqued my interest. I dont have the hands on experience that builders have but a general understanding of the concepts being discussed. I just found this video, right, wrong or indifferent to be quite informative
    Cheers
    Rob
     
    Tokin and Handy Andy like this.
  7. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

    Joined:
    Apr 23, 2018
    Messages:
    3,280
    Likes Received:
    3,607
    That's some great stuff right there...

    Fun to watch - well - at least I enjoyed it.

    Sorry, it's not Star Wars, it's better, much better, than that.

    There will be a Quiz on this later.
     
    Tokin likes this.
  8. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

    Joined:
    Oct 23, 2017
    Messages:
    3,221
    Likes Received:
    4,162
    Welcome!
     

Share This Page

  • About Us

    The WorldwideDX Radio Forum was originally established in 2001. We pride ourselves on welcoming Radio Hobby enthusiasts of all types, while offering unbiased, informative, and friendly discussion among the members. We are working every day to make sure our community is the best Radio Hobbyist's site.
  • Like us on Facebook

  • Premium VIP Member

    The management works very hard to make sure the community is running the best software, best designs, and all the other bells and whistles. Care to buy us a beer? We'd really appreciate it!

    Donate to us!