[Amps] Expert 1k amp

[Paul Christensen]

Steve,

I did an unscientific check with my SPE 1K.  Ripple on the RF envelope at 
the 1KW level is no worse than with my Alpha 77Dx and 87A at 1500W.  It's 
just noticeable on the scope at the maximum power level.   Yes, total drain 
current is about 40-42 amps.

If the QST Product Review is any indication of the amp's IMD performance, 
3rd-order 2-tone is about -40 dBc.  Not sure how well that figure holds up 
across a sample of units.  The IMD spectra of the 2K model appears very 
close.  Apart from fault detection and T/R, I've not spent much time with 
the rest of the schematic so it would be interesting to see how they achieve 
reasonably good IMD at full power that's competitive with many VT amps.

These are not "brick-on-the-key" amps.  In the case of the 1K, the software 
automatically cuts back power to 50% after about 15 seconds.  I don't run 
high duty-cycle modes like RTTY, but I think it would be a painful 
experience in a contest between automatic power reduction and fan noise. 
For me, it's a good instant-on alternative for my operating modes, but it 
would not be my only amp.

Paul, W9AC


----- Original Message ----- 
From: "Steve Thompson" <g8gsq72 at gmail.com>
To: <amps at contesting.com>
Sent: Thursday, March 07, 2013 3:50 AM
Subject: [Amps] Expert 1k amp


> Yesterday I did some minor repairs to a friend's amp - resoldering joints 
> on the current sensing resistor. Looking at the circuits later I noticed 
> that the main supply voltage is regulated by having SCRs in place of 
> diodes rectifying the transformer secondary and the main smoothing 
> capacitor is 47000uF.
>
> My friend tells me the amp runs over 40A at full tilt, which means 
> something like 8.5V ripple on the supply (7V at 60Hz). That strikes me as 
> quite high and I'd expect to see some difference in amplifier gain/output 
> if I was running such an amp off a regulated supply and altered the 
> voltage that much. Has anyone measured one? Is any 100/120Hz audible on a 
> carrier?
>
> Steve
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