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Reviews Categories | Electron Tubes | Eimac 3CX3000A7 Help

Reviews Summary for Eimac 3CX3000A7
Eimac 3CX3000A7 Reviews: 9 Average rating: 5.0/5 MSRP: $prices varies
Description: High-Mu forced air cooled Power
Product is in production.
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W0FEN Rating: 5/5 Feb 17, 2017 19:07 Send this review to a friend
3CX3000F7  Time owned: more than 12 months
The 3CX3000F7/8162 high-mu forced air cooled
power triode provides relatively high power output
as an amplifier, oscillator, or modulator at low
plate voltages. The tube has a low inductance
cylindrical filament tank circuit for VHF operation.
Operation with zero grid bias in many applications
offers circuit simplicity by eliminating the
bias supply. Grounded-grid operation is attractive
since a power gain of over twenty times can
be obtained. The 3CX3000F7/8162 tube is identical
to the 3CX3000A7 except for the addition of
flexible leads on the base for grid and filament
connections which can simplify socketing in low
frequency applications
3CX3000F7 / 8162

Plate Dissipation (Max.) 4,000 Watts
Screen Dissipation (Max.) ---
Grid Dissipation (Max.) 225 Watts
Frequency for Max. rating (CW) 30 MHz
Amplification Factor 160
Filament/Cathode Thoriated Tungsten
Voltage 7.5 Volts
Current 51.5 Amps
Capacitance Grounded Cathode
Input 38.0 pf
Output 0.6 pf
Feedthrough 24 pf
Capacitance Grounded Grid
Input 38 pf
Output 24.0 pf
Feedthrough 0.6 pf
Cooling Forced Air
Base Special with Flying leads
Air Socket ---
Air Chimney ---
Boiler ---
Length 18.437 in; 468.30 mm
Diameter 4.15 in; 105.50 mm
Weight 7.0 lb; 3.2 kg
ZENKI Rating: 5/5 Oct 17, 2015 19:26 Send this review to a friend
Clean and Rugged  Time owned: more than 12 months
Great to see more reviews of my favorite tube. A tube that I have been using for decades.

1. Super clean probably the best IMD performance available.
2. Rugged as Hell
3. It can be rebuilt if its a genuine Eimac
4. Will outlast most of us. A lifetime buy even in contest duty.
5. Its bargain price
6. Its for real hams, you not going to see a commercial amp with one from Ameritron! Get the tools out and build the amp, its really very easy. You cant pop a 3cx3000 like a fuse like you can with a dirty russian tetrode unless you are brain dead!
7. Its instant on and I can tune it once and maybe tune it every 5 years. Makes it easy to remote the amp. Its as convenient and fast as a solid state amp. Why would I even think of buying a filthy splattering mega dollar solid state amp when i can have the same convenience with a 3cx3000 for much less money and better performance?

8. Theres nothing bad to say about the 3cx3000.

In regards to the excessive power. Its largely a waste of electricity, power and money. If you cant do it with a 1kw to 1.5kw you really need to spend more on antennas rather than using more output power. The capabilities of the tube are generally wasted but thats only because you dont need it. If you want a QRO signal 1kw with a stacked array will do it for you, not 5kw with a G5RV in the attic from EBay!

I will change to another amplifier device like a LDMOS amplifier when they can match the IMD performance of the 3cx3000. I will be in the grave by the time that that happens. The same could be said for the driving transceivers which insults this excellent tube by driving it with such filthy signals from the radios.

KD5OEI Rating: 5/5 Oct 17, 2015 11:51 Send this review to a friend
Rugged and proven to give long service  Time owned: more than 12 months
This tube gets high marks. I have a lot to say about using it. If it's too long, skip it.

It is usually the case that when a properly designed amplifier is driven to a fraction of its capacity that the distortion is lower than if it were driven near its capacity*.

In the usual amateur use, it's impossible to overload the 225W grid with a 100W PEP transmitter. According to the Eimac data sheet, at a plate voltage of 4000V, 420W is needed to drive the tube to 6030 Watts output. The beauty of this is that a typical 100W PEP 'plastic radio' ham transmitter would drive it to 1436W. Of course the plate voltage can be moved around a bit with a variac to fine-adjust the power, but there's no logical reason to nitpick the difference between 1436 and 1500W. (some people will, go figure..) Anyway the Eimac specifications are just a set of proven guidelines. It's really a prefect tube for the ham wanting a full power amplifier. Some other fairly common high power tubes like the 4CX5000 are tricky to drive in grounded grid because the grids are asily damaged in case of a mistake or fault.

Builders are concenred about cost, weight, and size. There's no way to avoid the filament power requirement and adequate cooling, but there is no absolute need to use pole-pig-like plate iron if one is happy with the power supply imiting the performance. Smaller power supply parts could make for a ligher weight power supply, but a small supply is also subject to regulation issues and poor regulation will amplitude-modulate the signal.

Speaking of cost, tube replacement cost is outrageous for certain types. The 3-1000Z is possibly not made any more, and a like new industrial-rated Amperex one is $750. The 4-1000 can be had cheaply, but a 1KW dissipation rating is not conservative for use on AM in a 1500W PEP situation. It's the low efficiency at caqrrier level that wants to eat up tubes. The 3-500Z is OK, and fairly cheap, but they are all Chinese-made now and can't be pushed too hard. A pair is marginal. Three might be OK. The 3CX3000 os a very good choice. It has a higher one-time cost, maybe $750 for a rebuild, but it's not going to burn out over the life of the equipment when used at ham power levels. For those worried about filaments, a soft start to limit inrush current is worthwhile there.

Serious builders want everything to match up. A tube capable of 6500W output needs a 10KVA power transformer. A 5600V 2A transformer will make a solid 4300V at 2A using a 30H choke input filter wit a 10uF capacitor.
A transformer for this can be made by restacking the core of a 3-phase 20KVA transformer from an old RCA Amplidyne broadcast rig. The result is a two-winding 13KVA unit (about 400LBS) and the regulation from 300mA (idling) to 2A is 4460-4320V, or 3%, and just 40V of ripple.
That is how a power supply should perform. The above are all CCS (Continuous Commercial Service) figures, not ICAS and not the oft-used "SSB" rating of IVS (Intermittent Voice Service) found in amps like the SB-220 that have a 40-70uF capacitor-input filter and regulation of 20%.
Beside good regulation, the choke input filter using a reltively small 10uF capacitance limits the fault energy in caeof an arc. A high voltage fuse should be employed anyway.

I have a nice 3CX3000 amp that was built by someone else. It was built so well that i thought it had been factory-made. It will definitely make 6KW peak power but uses a small 2.6KVA (CCS) transformer with a voltage doubler and huge stack of electrolytics, so the regulation is not the best (22%) if it is pushed. However, it easily will make legal limit power in any mode all day long with decent regulation of around 8%.

But I am building a 3CX3000 amplifier for myself and want a full duty piece of equipment with the best regulation and no question about there being a weak link somewhere, as was done in the old days when hams wore a coat and tie to ham fests. My TS-430 is ready to drive it to the nominal 1430W PEP.

I'm astonished by the 'no' reply in the topic and wanted to learn more about why someone would be so much against a 'Cadillac' solution, but the person wo made the post is not identified at all, so the opinion can only be discarded as meaningless.

* A case in point is the old Elenco Commander*, a 4-1000A GG amp running 6000V on the plate and having a 4KW PEP input rating and 1500W average input on AM, made from 1958 to 1959, was designed with this concept in mind. A 4-1000 would not stand up to 4KW PEP input if used on AM, but it is perfect for legal limit use in that or any mode including. It's documentd in "Transmitters, Exciters and Power Amplifiers 1930 to 1980", by Raymond S Moore. The manual is online somwehere. Even with these good specs, a 4-1000 is nearing its dissipation limit when used as a linear amplifier for AM, and the grids are at risk, especially the 25 Watt control grid, unless the higher plate voltages are employed to increae the tube's sensitivity.
WA0ZZG Rating: 5/5 Jul 20, 2012 18:34 Send this review to a friend
Knowledge Builder  Time owned: more than 12 months
The company that makes this tube, Eimac, is actually owned by a parent company, CPI. One of the other CPI divisions is a company called Econco. These people take tubes like this, tear them down and rebuild them. Cost can be quite a bit less than new from Eimac. Econco does grade their tubes. You have to ask.
You will also gain a fantastic understanding of power tubes by reading their 'Tube Topics' section. Filament voltage is EXTREMELY critical here. You need to use an adjustable, regulated filament supply that can produce 7.5V at 54amps.
I had a tetrode in a 5kw FM transmitter(4CX5000) that normally gave 27,000 to 30,000 hours fail at 7000 hours because I left the filament voltage turned up, and it was at 8.0V.
The air blower will sound like a Hoover. 220V, single phase may be at the limits and 3-phase may be needed. I like step-start relays at this size and a fan cooldown timer.
This is the size where transmitters are hand built, never on an assembly line. It is as much an art as it is a science. ..and the trees glow and the bushed hummm..
KB8YIJ Rating: 5/5 Jul 19, 2012 23:53 Send this review to a friend
Yes use it in ham radio!  Time owned: more than 12 months
The posting that was saying not to use in ham radio is frankly dumb. Im a broadcast engineer and all transmitters are built with plenty of headroom.

I would much rather have a tube that will last longer than me and is almost impossible to hurt for tuning mistakes than a weak kneed over priced tube that fails all the time.

As far as illegal power goes who says you need a giant pwr supply to run this tube?? How many sets of 3-500z amps are out there running 4000+ on the plate?

How about the hf radios that run 200 watts out you think that some hams are not running more than 100 watts into a amp like a sb 220 or something like that. Can you say wide?

Or better yet put 200 watts into something like a a amp that uses 3cx800s or any tetrode poof is what happens a lot of the time and all of this because you forgot to turn the output down.

Then you get to get new tubes that are WAY overpriced and very sensitive to tuning mistakes.

As far as I'm concerned for the money you can't do much better than the 3cx3000a7 or better yet the F7 version.
VE7RF Rating: 5/5 Dec 16, 2011 06:54 Send this review to a friend
Superb-best tube for IMD..period.  Time owned: more than 12 months
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
K6AER Rating: 5/5 Sep 25, 2009 13:49 Send this review to a friend
Solid tube for amplifiers  Time owned: more than 12 months
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.
K8KAS Rating: 5/5 Sep 25, 2009 08:26 Send this review to a friend
Lot's of reserve  Time owned: more than 12 months
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.
HFRF Rating: 5/5 Sep 25, 2009 07:17 Send this review to a friend
Ham use? No!  Time owned: more than 12 months
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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