[Amps] Expert 1k amp

[Carl]

Is the ARRL still using a 6dB fudge with the way they measure IMD?

Carl
KM1H

----- Original Message ----- 
From: "Paul Christensen" <w9ac at arrl.net>
To: <amps at 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 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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>
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