[Moon] REPRINT of W6PO Amp Re: [Moon-Net] 3CX1500 PA 144

Thu Aug 27 15:47:52 CEST 2015

Hi All,

If Interested in original amp,
 this is my tuning I used for 8877 amps.
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Tuning of amp power out is G1 "grid current peak" critical,
do not to exceed G1 rating for plate voltage/current and input drive,
adjust drive, plate load and plate resonance for recommended G1 current at power out peak watts.
--------.
Reprint of W6PO amp. is:

http://www.landfall.net/Radio/8877-1.htm

L1 = (CTC 1538-4-3) try AMIDON T-50-12  # 22 - 7T,
 as you find on gauge wire with # turns needed for best G1 vswr.

Tom  W2DRZ
  ----- Original Message ----- 
  From: w2drz at ramcoinc.com 
  To: TexasRF at aol.com ; radeohedca at hotmail.com ; w8zn54 at verizon.net ; faustocoletti at alice.it ; moon-net at mailman.pe1itr.com ; moon at moonbounce.info 
  Sent: Wednesday, August 26, 2015 3:27 PM
  Subject: Re: [Moon] [Moon-Net] 3CX1500 PA 144

  Hi Hugh,

  The tube at rated power and proper drive the cathode is about 54 ohm,
   be sure the proper 50 watt zanier is installed in circuit so bias does not change with plate current up to 1 amp.

  What is needed is a low Q input cathode circuit, many years ago went thru the same problem with the 8877 tube..
   original design with ferrite core form is the main problem today, as that part is no longer made and do not recall the core mix.

  Gerald is correct on description of circuit.
  to find a replacement slug form is close impossible.
   So best is attempt a low Q input circuit design..

  tom W2DRZ

    ----- Original Message ----- 
    From: TexasRF at aol.com 
    To: radeohedca at hotmail.com ; w8zn54 at verizon.net ; faustocoletti at alice.it ; moon-net at mailman.pe1itr.com ; moon at moonbounce.info 
    Sent: Wednesday, August 26, 2015 2:39 PM
    Subject: Re: [Moon-Net] 3CX1500 PA 144

    The input impedance of a cathode driven amplifier is related to cathode current. That makes the required impedance matching solution quite different for low drive power vs high drive power.

    With very high drive power the cathode impedance is fairly close to 50 ohms resistive. In this case the input matching network is there mainly to cancel the cathode to grid C component.

    With lower drive levels, the network would still cancel the C but would also transform the much higher R value down to 50 ohms.

    73,
    Gerald K5GW

    In a message dated 8/26/2015 12:47:07 P.M. Central Daylight Time, radeohedca at hotmail.com writes:
      Keyphrase "...should be able to..."
      I beat my head against the wall trying many variations on the original T network to get it to work properly. It looked good into an antenna analyzer (low power) but acted differently with real power going through it. I concluded that it was insufficient to satisfy my FT-847 so a more coplex network is required. 

      73, Hugh VA3TO

--------------------------------------------------------------------------
      From: w8zn54 at verizon.net
      To: faustocoletti at alice.it; moon-net at mailman.pe1itr.com; moon at moonbounce.info
      Date: Wed, 26 Aug 2015 13:26:37 -0400
      Subject: Re: [Moon-Net] 3CX1500 PA 144

      In the original W6PO circuit, there was a variable inductor, a variable capacitor and a fixed coil. By adjusting the two coils and cap, you should be able to get the input SWR down to less than 1.5:1. I’ve used an MFJ and a Comet antenna analyzer to do this with decent luck.

      GL and 73,

      Terry – W8ZN

      From: moon-net-bounces at mailman.pe1itr.com [mailto:moon-net-bounces at mailman.pe1itr.com] On Behalf Of Hugh Duff
      Sent: Wednesday, August 26, 2015 1:06 PM
      To: Fausto Coletti; moon-net at mailman.pe1itr.com; 'freetalk moonnet'
      Subject: Re: [Moon-Net] 3CX1500 PA 144

      I had a similar experience with my W6PO amp. 

      I was driving it with a Yaesu FT-847 which seemed to be extemely sensitive to SWR and it dramitically folds back the output power.

      I ended up using an MFJ 2m atenna tuner between the radio and the amp and it worked perfectly, low SWR and maximum power transfer. 

      My next step would be to build up an more complex input network.  

      73, Hugh VA3TO

--------------------------------------------------------------------------

      From: faustocoletti at alice.it
      To: moon-net at mailman.pe1itr.com; moon at moonbounce.info
      Date: Wed, 26 Aug 2015 17:54:20 +0200
      Subject: [Moon-Net] 3CX1500 PA 144

      Hi all, 

      I am building for a friend a 3CX1500 linear amplifier for 144 MHz. 

      At the first tests, the amplifier work well with a good gain, 20 Watt input for 800 watts output. 

      The problem is in the input circuit or, if I set it to a low SWR, I have not the maximum power transfer 

      and vice versa if I set for maximum power transfer I have a high input SWR. 

      I used a T circuit as the W6PO amplifier. 

      Any suggestion? 

      73, Fausto IK4NMF

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