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write your own review of the Eimac 3CX3000A7.
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VE7RF
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Rating: 5/5
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Dec 16, 2011 06:54
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Superb-best tube for IMD..period.
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Time owned: more than 12 months
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50 watts in = 1.5 kw out
100watts in = 2.5 kw out
150watts in = 3.5 kw out
200watts in = 5.2 kw out
That's all at 5kv under load. [5500 no load]
The joke is, you can use the 225 watt CCS grid as a Dummy load for your 200w FT-1000D. It's also rebuildable. It's NOT your typ throw away tube. The IMD is superb, 2nd to none. I used a pair of dayton 4C006B blowers to cool it. Socket came from RF parts. Chimney is a modified SK-306, with wraps of silicone rubber around the tube,and a SS hose clamp to fill the gap. The tube is built like a tank. Harbach sells Dahl fil and plate xfmrs. I used a Sola constant voltage xfmr, to feed a constant 240 vac to a small 5A, 0-240vac variac, that feeds the fil xfmr. Just the fil + blower on for the 1st 48 hrs, since it uses getters that are heat activated from the fil. Use 7.5 vac, measured at the socket, for the 1st 200 hrs. After 200 hrs on the fil hr meter, fil V reduced to 7.125 vac. Ramp it up slow..and when done fro the night, ramp it down slow, then leave blower on for another 10 mins.
This tube is a HUGE bang for the buck..and so is it's big brother, the 3CX-6000A7, also superb.
[both take the SAME socket]
later...Jim VE7RF
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K6AER
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Rating: 5/5
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Sep 25, 2009 13:49
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Solid tube for amplifiers
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Time owned: more than 12 months
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I have used the 3CX3000A7 and it is a great tube. Tube mounting is a bit of an engineering function but if you have access to a machine shop this is but a 3 hour issue.
Filament and cooling tend to be the largest issues. The filaments require 386 watts at 7.5 volts but the tube is instant heat. At amateur power with 4000 volts on the plate I have measured 46 dB IMD from second to third and the tube at 1500 watts out and this makes for a very nice AB2 linear. Even when not in use it make a nice shack heater.
Air pressure is a bit high for ham desktop applications requiring a lot of air and some might find the tube application noisy.
Input capacitance is 38 pF and the tube works very well up to 6 meters. The largest single problem is the tube gain (amp factor 160) is high and you need to use an input pad if you want to drive the tube with typical 100 watts.
With Thoriated Tungsten filaments you are ready to go in seconds which is nice. Finding a 51 amp filament transformer was the hardest part of the project.
I built my amplifier as a stand alone cabinet and eventually sold the amplifier to a contest station.
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K8KAS
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Rating: 5/5
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Sep 25, 2009 08:26
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Lot's of reserve
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Time owned: more than 12 months
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I would much rather listen to a good 3CX3000A7 than some 1 watt QRP station. It's a great tube and a lot of ham's have used them over the years.
PS--If you don't like QRO all you have to do is turn the dial, don't cry about it. QRO can be a great trainer as well for some people, because QRO ham's know when you do run power a lot of thing's can smoke and bake if your cheap. It's also a great way to meet your neighbors fast.
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HFRF
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Rating: 5/5
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Sep 25, 2009 07:17
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Ham use? No!
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Time owned: more than 12 months
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The tube is meant for commercial broadcast which means very long life with very reliable service. The tube is relatively cheap considering the 5-10 kilowatts that can be delivered. Using this tube for ham use is stupid unless you want to run illegal power levels. Then why stop here. Maybe a 3cx20000 might be better for all you illegal hams and cbers. 350 watts to heat the filament and a large chassis and blower would be required. Any normal use of this tube for a ham amp is retarded. The theory that an amp with huge power capability used at ham power levels will provide service that will last a million years is dumb. These amps tend get dismantled in a short time while lowly SB220 last 50 years.
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