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Re: [Amps] Expert 1k amp

To: "Paul Christensen" <w9ac@arrl.net>, <amps@contesting.com>
Subject: Re: [Amps] Expert 1k amp
From: "Carl" <km1h@jeremy.mv.com>
Date: Thu, 7 Mar 2013 11:58:27 -0500
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Is the ARRL still using a 6dB fudge with the way they measure IMD?

Carl
KM1H

----- Original Message ----- From: "Paul Christensen" <w9ac@arrl.net>
To: <amps@contesting.com>
Sent: Thursday, March 07, 2013 8:06 AM
Subject: Re: [Amps] Expert 1k amp


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@gmail.com>
To: <amps@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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