[Amps] Expert 2K / lack of specs /

[Joe Giacobello, K2XX]

I believe that some on this forum were interested in the IMD specs for 
the 2K.  The data that were generated for FCC approval can be found 
here:  http://g4ujs.shacknet.nu/spe_2k-fa.pdf

They seem pretty good.  The thing that bothers me is that the drive they 
used to obtain 1,500W out was about twice what I require.  Makes me 
wonder if the unit that was used to generate the data was different from 
those currently on the market.

73, Joe
K2XX

On 3/10/2013 9:19 AM, Jim Thomson wrote:
> Date: Wed, 6 Mar 2013 11:18:18 +1030
> From: "Leigh Turner"<invertech at frontierisp.net.au>
> To:<amps at contesting.com>
> Subject: Re: [Amps] Expert 2K / lack of specs / pragmatism prevails
>
>
> When homebrewing big SS amps I've found designing 'em big and de-rating them
> a couple of dB below sat Po yields plenty adequate IMD performance for clean
> ham band SSB use. Certainly commensurate with the IMD of modern transceiver
> PA stages and their associated ALC Tx power control loops.
>
> Inefficiency is the inevitable trade-off one makes when wanting to run the
> SS amp clean.
>
> Leigh
> VK5KLT
>
> ##  leigh, there would be no loss in eff, IF you used bigger devices, or more of them.
> The inefficiency starts up when you design a 1 kw amp,,and then operate it at 500w.
> Its cleaner at 500w, but its inefficient.  Reduce the voltage a bit, like 41%, and eff
> is back on track, but imd suffers due to lower voltage used.
>
> ## Instead, used devices rated for 2 kw output, design the amp for 1 kw output,
> run the highest voltage possible and eff will be  as high as it gets.   IMD will be a lot lower,
> and devices will run cooler.   Trade off is you require more devices or bigger ones.  heck,
> the cooling can be based on 1 kw output, and also the pwr supply.
>
> ##  enough of these freescale devices may be the ticket. loads of power
> AND low imd for a change.   Just cuz you don’t hear imd when listening to
> an S-9 signal on a noisy band doesn’t mean there is no imd.  listen to the
> same station, but at 40 over S-9, on a quiet band, and presto, imd is easy to
> spot.   If IMD is only 30 db below pep ( arrl method), IMD  will be 10 db
> over S-9.   IMD really needs to be down  60 db below pep, when listening
> off freq.
>
> ##  Its’ the IMD 7-9-11-13-15th that causes all the problems.  Class A  and some type
> of sliding bias scheme would work  or the eq of EBS.   Or just operate the devices at
> well below their max ratings, like 1/3 their rating.
>
> ##  You don’t see this lousy imd in the commercial /marine/aviation world.
>
> Jim  VE7RF
>
>
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