[Amps] IMD

[jeremy-ca]

As Ive already mentioned I do my IMD tests at 600W after tuning up at around 750W or wherever the tubes "land" with rated Ig or a bit less. Typical for those 3 points is in the -32 to -37 dB range. Loading is critical to maximizing the IMD.

The only time Ive seen 7.5dB gain is with tired tubes. Full output ones can run as high as 11-12 dB with 10 being the norm. This last amp which prompted the thread was doing 900W with a bit under 100W drive, I didnt leave it on more than a few seconds. Backing down to 50W yielded 750W at 55% efficiency.

Im not overly concerned about the rated dissapation, that was derived for CCS audio service for which the tube was originally designed by Taylor.

Depending upon which spec sheet you read the max Ep can be as high as 2750V, Cetron was just one of many building that tube in the USA or Europe.

It's a whole lot easier to tune a 6M amp with selected C values as compared to say using a 250pf Tune and 850 pf Load on 10/15M as is the norm with the HF amps. Fast tuning means the plates dont even show color and once set leave it alone.

If you look at the AL-1200 specs they claim 1200W with 3 tubes so no matter how anyone wants to spin it Im not doing anything different at 750W with two.

End of discussion finally I hope.

Carl
KM1H




  ----- Original Message ----- 
  From: Steve Katz 
  To: Gudguyham at aol.com ; la7sl at online.no ; amps at contesting.com ; km1h at jeremy.mv.com 
  Sent: Tuesday, September 25, 2007 4:37 PM
  Subject: RE: [Amps] 6 mtrs:


  Yep, things do change.

   

  I want to see the spectral analysis of the SB-200 (monoband or otherwise) operating at 750W PEP output on SSB, closing in on IM3-5-7 especially.

   

  When I've used this tube, it's provided only about 8 dB power gain.  With 100W drive that's <750W output, at any frequency.  The Cetron "ratings" per the old data sheet I have is 30 MHz max for full ratings; 7.5 dB gain; 2.4kV max and 250mA max per tube, yielding 300W output per tube (the data obviously assumes 50% efficiency).  At even 65% efficiency to achieve 750W out would be 1153W in, and 403W dissipation from a pair of tubes rated for 320W max dissipation at 30 MHz.

   

  I fully agree anything's possible.

   

  WB2WIK/6

   

   


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

  From: Gudguyham at aol.com [mailto:Gudguyham at aol.com] 
  Sent: Tuesday, September 25, 2007 1:28 PM
  To: stevek at jmr.com; la7sl at online.no; amps at contesting.com; km1h at jeremy.mv.com
  Subject: Re: [Amps] 6 mtrs:

   

  In a message dated 9/25/2007 12:36:55 P.M. Eastern Daylight Time, stevek at jmr.com writes:

    But driving a pair of 572B's to 750W output  looks to a retired E 
    professional
    like pushing an old VW beetle to 100MPH would look to an auto engineer:
    Risky,- at best :-)
    May be I am too conservative ??? ...

  Hi Steve, the Sb-200 operators manual says that 100 watts is permissible,  Just because you are used to an SB-200 on HF or similar amplifier that with 100 watts makes only about 650 watts out, then why is the same 100 watts of drive any different on 6 meters?  To me, 100 watts drive is 100 watts drive either on 80 meters or 6 meters.  I think some of you guys have to think "outside the box".  When one fine tunes a design and makes it specific for a specific frequency we are talking a horse of a different color than an all band amplifier.  Things change.






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