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• Surplus UHF NEC Amplifier Modules

• Surplus UHF NEC Amplifier Modules

  ZL1SWW > 12-03-2017, 04:34 PM

  Hi,
  
  I was lucky to get one of the ex UHF TV PAs here in ZL from a very kind VK3.
  
  On the old VKlogger forums, there was a discussion about these and the VK3BEZ club had been selling these?
  
  I have changed my Pots and set up the initial bias conditions etc without Drain power.
  Started on the Wilkinson combiner and just wanted to ask a question relating to the power rating of the 100 ohm isolation resistor.
  The one in the pictures looks like about 30 watt or so.
  
  Now all things being equal etc, shouldn't see too much power dissipated in this resistor. Just wanted to gauge what people have found who have fired this up with success. Nay heat showing up and should I use say 100 ohm 100 watt? I can series up two 50 ohm ones that have leads out each side and the heat sink tab isolated.
  Have put mine on a bigger and straighter heat sink.
  
  Refer to about the 3rd pic etc in the pdf.
  
  http://www.vk3bez.org/Files/Surplus%20NE...odules.pdf
  
  Cheers and thanks for any feedback.
  
  Simon
  ZL1SWW

• Re: Surplus UHF NEC Amplifier Modules

  VK3WRE > 13-03-2017, 09:14 PM

  Hi Simon, the load in the kits we sold were 50 watt units, I didnt do any damage to the 100 ohm load when I distroyed one of the
  fets in the prototype unit. 2 of the 50 ohn resistors will fit the bill if you have nothing else on the combiner.
  I have done quite a few units to date and all have worked well with only a couple of blown fets !!
  good luck with the unit.
  
  cheers Ralph
  VK3WRE

• Re: Surplus UHF NEC Amplifier Modules

  ZL1SWW > 16-03-2017, 04:47 PM

  Hi Ralph,
  Yeah I hope mine will work!
  
  I have 30 Watt 100 ohm resistors. By rights if all things are balanced, we shouldn't see too much heading into the load.
  I might try a 30 Watt one as it is the only one I have bar the two 50 ohm double lead types. Just means I have to splay the coax apart a bit at the input end.
  Will take care that the short 50 ohm coaxes leading to the combiner at exactly the same length.
  
  Cheers & thanks,
  
  Simon
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