I've used the Gamma on PSK at 30 watts and CW at 100w and no one complained (I realize that only means no one complained). I may have been pushing the envelope but the Gamma met my needs for a small lightweight portable supply. I wouldn't use it full time in the shack when there are other more robust choices.
Buck k4ia K3 #101 In a message dated 8/18/2010 11:57:34 A.M. Eastern Daylight Time, [email protected] writes: > *Gamma Research further hedges their rating by adding a footnote > to their spex that "Output power should be limited to 25 or 300 > watts during tune-up or other prolonged key-down operation." At > 13.8 VDC that means the supply should not be expected to provide > more than 2A continuous! With a less than 50% DC to RF efficiency for most solid state rigs (K3 is 36% based on 20A @13.8V for 100 W output), 25 or 30 Watts output would be close to 5 Amps @ 13.8V assuming 40% efficiency. 73, ... Joe, W4TV On 8/18/2010 11:39 AM, Ron D'Eau Claire wrote: > Quite true Joe, and that's why it's important to note how the supply is > rated. > > If you're talking about the Gamma HPS1a, it's rated at only 5 amps > continuous* and they do not offer an ICAS rating. Instead they say it will > handle 22 amps peak at 25% duty/sec., which I interpret to mean no more than > 22 amps for up to 250 milliseconds during any 1 second interval. Clearly > that's useless for supplying anything but SSB voice modulation, and I'd be > concerned with using it with any degree of compression at that. I'd never > expect it to support RTTY or FM with the K3 above 10 watts RF output where > the current demand exceeds the 5 amp rating of the HPS1a. > > By comparison the MFJ-4125 with its 22A continuous, 25 A peak rating should > allow you to put a brick on the key at 100 watts with *most* K3s feeding a > low SWR. K3's can be well with in factory spec's and show a variation in > current demand of a few amps at 100W RF out from rig to rig and band to band > and, of course, the SWR has a big effect on the current needed. > > As I noted, with my K3 if I were to run a 100% duty cycle mode like RTTY or > FM and planned to transmit more than 5 minutes at a time, I might dial back > the RF output power 1 or 2 dB to keep the Astron 20A within its CCS rating. > > Ron AC7AC > > *Gamma Research further hedges their rating by adding a footnote to their > spex that "Output power should be limited to 25 or 30 watts during tune-up > or other prolonged key-down operation." At 13.8 VDC that means the supply > should not be expected to provide more than 2A continuous! > > -----Original Message----- > > I run my K3 from an Astron 20A with no problems at all. The 20A > > is rated at 20A Intermittent Commercial and Amateur Service (ICAS) > > and 16A continuous commercial service (CCS). > > Ah, but there is a significant difference in the rating between > a linear supply (your Astron RS-20) and a switching supply like > the MFJ-4125 or similar. The Astron is rated for average current > and duty cycle ... it can almost certainly provide more than 20A > on short peaks ... the 20A rating is based on heating of the > transformer and regulator transistors. > > A switching supply is generally rated for CCS with peak current > rating based on the energy storage in the capacitors (how much > current can be drawn before the output drops too low) and the > average current based on the capacity of the switching circuit > to keep the capacitor charged (current rating of the inductor, > transformer, and switching devices). > > A prime example of the peak/average issue is the Gamma supply. > It does not even tolerate full power CW well at slow speeds and > falls apart completely at 100 W (even 50 W) RTTY because of the > "continuous" current limitations. > > The K3 is quite happy with a 25A peak / 20-22A continuous > switching supply. Since a linear supply generally has sufficient > energy storage in the filter cap because of the need to work with > a much lower ripple voltage than a switcher, a "20A" linear supply > can usually supply the same brief 25A peaks (dynamic load) within > the heating limits of 20A (average) ICAS service depending on the > design of the regulator (current limiting). > > 73, > > ... Joe, W4TV > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
