[Amps] SPE 2K RTTY Duty Cycle

[Jim Thomson]

Date: Fri, 22 May 2015 07:58:01 -0500
From: Kevin Stover <kevin.stover at mediacombb.net>
To: amps at contesting.com
Subject: Re: [Amps] SPE 2K RTTY Duty Cycle

There are NO 12V final amateur transceivers that make -40dB IM3, none. Never have been, never will be. The best are at -33 to -35.

Those transceivers capable of 200 Watts are all using 28 or 50V finals and can reach -40 depending on the low pass filter used behind the PA.It's time for the manu's to get rid of this fascination with running evberything off a battery.

The most expensive part of any SS amp is NOT the finals themselves it's the LPF that will take 1500 watts and keep harmonics legal (-43db HF, -60dB 6m). That's not IM3. Name the amp that hits an IM3 of -40. The 8877 will come close, the Russian triodes won't, none of the tetrodes will do it.


-- 
R. Kevin Stover
AC0H

## The old Icom marine transceivers, that were the size of a Icom 720   would easily meet FCC imd specs for marine SSB.    And yes, they all ran on 12 vdc...still do.   Baffles me why Icom and Yaesu can easily make marine SSB HF
transceivers  that will meet the fcc  imd spec.....yet make pure junk for the amateur radio versions.   But, if you look at the 12 vdc marine gear, like the typ 2-30 mhz types,  you will see that the microphone is hardwired into the radio.  There
is NO mic gain control at all.  There is NO processor.   Fixed power output in most cases.   FCC marine IMD specs are sky high vs ham junk.  How do they do it..and with just 12 vdc?  Better final transistors, but de-rated for better IMD.
And loads more NFB.   And no, they don’t run Class A  either. 

##  If you want to see crap IMD... check out the 400watt version of the yaesu 9000.  -11db for imd3.   That’s like –17 db pep. 

##  Sure, the yaesu in class A has superb imd..... but its very inefficient..and runs extremely hot.   My yaesu  MK-V  sucks 10A  CCS in class A mode.  regardless of whether it putting out 0 watts..or 75 watts.   Do the maths.
It dissipates 300 watts, when keyed, but no audio.    And 225 watts, when keyed, and driven to 75 watts out. 

##  If you want a triode tube amp that has superb imd, is instant on, and uses a rebuildable tube, the 3CX-3000A7 is the real ticket.   IMD3 = –59db pep.  That’s –53 db  below one tone of a 2 tone signal.  IMO, IMD referenced to  pep
is valid.   S meters are peak reading devices.  If a 40 over S9 signal is S9 a few khz away, its imd is –40 db pep. 

##  I have given up trying to find a SS amp that meets my requirements.  Maybe way down the road, but not these days.   Dunno what all the fuss about MRF-150s is all about, ther device is long gone obsolete.   The latest version, the 
VRF-151G is far better in every aspect, including imd. 

Jim   VE7RF