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4cx800 amplifier how to

Up Home. This page might be a bit long, but it explains how and why you need to adjust the amplifier in a certain way. If you find it confusing and have suggestions to improve it, please email me at this address:. In grounded-grid amplifiers , grid current meter is the single most important indication of proper final loading and operation!!


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WATCH RELATED VIDEO: JTG Built 4cx350 Steel Tube, base linear Amplifier

144 MHz Amplifier with GU74b


If you cannot hear them, you cannot work them. So, before buying an amplifier, install the very best antenna system you can afford. The best example of a compromise antenna is a G5RV because it was designed to provide great results only on 20m — on every other band it is a compromise and on 80 it gives very poor results, on it is little better than a Dummy-Load.

A good antenna system gives gain in two directions, receive and transmit. If you use a poor antenna, you will get poor performance in both directions. The BEST way to get cheap gain is to eliminate loss. This means you must design your antenna system specifically for your purpose. Do not ignore the loss in your transmission line. Although it is true that any given transmission line will exhibit less line-loss when used on the lower frequencies, it is still loss that can be prevented and transmission line loss affects both transmit and receive.

Only buy coax made in the USA and then only that made to military specifications. Stay away from any coax made in China. Ninety-nine percent of amateur radio operators find that when they use a reasonable antenna system, to watts of output power is more than enough power.

The reason behind this is simple…people can more easily understand and operate in watts but our equipment operates in Decibels Db. To appreciate this more fully let us relate it to the S meter and what it means when we increase output power. First, each increase of one S unit e. Therefore, to go from a reading of S6 to S7 you will need to increase your output power by 6 DB.

Using this scale, it means that every time you double your output power you are increasing your signal by only 3 DB. If you again double your output power you will get another 3 DB increase in signal strength. Together both these increases total 6 DB from your original power level. Here is a real-life example: you are transmitting at the watts output power level.

The ham on the receive end of your signal is seeing an S5 on his S meter. In order for him to see an S6 on his meter, you would have to increase your power output level by 6 DB or go from watts to watts of output.

In order to go from an S6 to an S7 on the receive end you would then have to go to watts of output power. Understanding that watts of output power is the legal limit, that is as close as you are going to get to an S7 meter reading.

If you have an amplifier that produces — watts of output power you will have an 8. If you go from watts to watts, you will have a 3 DB advantage, which is only one-half of an S unit. If you and your friend are both running watts of output power and both of you are giving the ham on the receive end of you signal exactly the same S meter reading, by you increasing your power to watts you will have a half of an S unit advantage which will get you through to the other ham first, all things being equal.

Most of the older and smaller tube amplifiers have little, if any, protection circuitry. You just had to watch how you tuned the amplifier. The only value the fuses offered were to give some protection after a catastrophic failure like a shorted power transformer.

If a tube shorted, the meters would blow and maybe the fuse would eventually blow. The first real level of protection amplifier manufactures incorporated in amplifiers was grid protection. If you drove the amplifier with too much power or did not tune the amplifier properly, you would over drive the grid s and damage to the tube s.

With grid trip protection, if the grid current went past a predetermined value, the grid protection relay would drop out and the amp went into a standby mode. Tube type amplifiers of today are either grounded grid or grid driven, class AB1 or AB2. These make for good linear amplifier designs. Some of the older amplifiers were grid driven class AB1 and could be driven into class C. You should not drive any amplifier into class C and use it on SSB. If you did, the signal would be distorted and cause splatter on the band.

Class C would be for CW only. Many years ago, amplifiers were rated on input power and class C would give an advantage of more power out with less power in.

Go to any forum on the internet that talks about amplifiers and you will see what I mean. These were a series of handbooks that gave, what I call, the best place to read and learn about RF amplifiers. He does not subtract drive power, from the radio, in his formula.

Example: watts of output power divided by watts of input power equals. Example: volts key down times ma equals watts of input power. Here is where efficiency really comes into play. It not only tells you how good of a job the manufacture did when they designed the amplifier but it tells you how to choose the proper tube or tubes for the RF section. Looking at the above formula, we can see the amplifier starts out with watts of input power but only produces watts of output power.

What happened to the difference in power of watts? Well, that is what the tube has to dissipate. If the tube is not designed to dissipate that much heat or the tube is not cooled properly, the tube will fail. Now the tube will have to be able to dissipate watts of power that is turned into heat. When it comes to transmitting tubes, the old dependable Z tube is still a great tube to use in RF amplifiers.

They are still reasonable in price, take a lot of abuse before failure, and produce a lot of power. A properly designed RF deck with a single Z is capable of producing watts of output power. I have never seen any design on the market that can do this without abusing the tube. The problem is, they are overdriving the tube, producing IMD on the bands and shortening the tube life.

Their plate voltage is too low and the tube is not cooled properly. The old B series tubes are still available and are still widely used. Four of these tubes will generally produce watts of output power. One of these tubes is capable of producing as high as watts of output power.

The tube is still readily available and can easily product watts of continuous output power all day long. Svetlana, a Russian tube manufacture, has been supplying tubes for amplifier manufactures for many years.

Pi and Pi-L refer to the tank circuitry in your tube amplifier. Pi-L uses an extra inductor or the addition of a unun in the tank coil assembly. A properly built Pi network will offer about 45 DB of third order harmonic attenuation. This will vary with plate load impedance and does comply with FCC specification. Pi-L offers 65 DB of third order harmonic attenuation and is not affected with plate load impedance. A second advantage Pi-L offers is smoother tuning on 80 and meters.

Power supply requirements can vary. This rating means the amplifier can put its rated power out, nonstop, 24 hours a day 7 days a week. TV and radio broadcast stations look for these ratings.

VA stands for Volt - Amp ratings. KVA is Volt - Amp rating. If it takes about watts of input power to produce watts of output power, a good choice for a rugged power supply would be a supply ratted at 2. If the transformer produces volts and can handle ma of current load, the transformer is rated at x.

If the transformer is rated at 2. Remember, there are bleeder resistors across the capacitors in the power supply and that will generate a partial load on the transformer. Watch how the manufactures advertise their power supply ratings; it is all in the wording. Very few amplifiers have high KVA ratings for their power supplies.

Most of them are rated well below the 2 KVA. The high rating is not really needed unless you are running a very high duty cycle. A VA power supply can easily supply a tube with enough power to produce a comfortable watts of output power. You can gauge the capacity of a transformer by its weight. A transformer that weighs 30 pounds has a capacity of watts of commercial service. These ratings are watts delivered to the RF deck, not power output from the amplifier.

This amplifier weighed only 47 pounds. Although the tubes were the weak link in this amplifier, it could run PEP watts out all day long and not overheat the power supply. I am not suggesting you look for a lightweight RF amplifier.

I am just trying to give you an idea of a duty cycle comparison between commercial service and amateur radio service. Solid-state amplifiers have come a long way and have become very popular with contesters. The reason is, they do not have to be tuned which makes for fast band changing. For these amps to produce watts out you must have a power input of watts. That means you have to dissipate watts of heat. SS devices are not as forgiving to high SWR or over driving as tube type amps.

SS amps have a lot of protection built in. They trip if the SWR goes over 1. Watch carefully how you treat a solid-state amplifier.


Gu74b for sale

Rcmp ottawa jobs I am still experimenting with this design, but the information is sufficient for a home brewer! The first design. The second design. Recent experiments with a stripped design. Fitted with an electronic bias switch. Trial version second design.

ARRAY Solutions sells OM Power and Acom HF Amplifiers -- BOTH which use the 4CX Tetrode. These Tetrode RF Tubes were $ USD for a.

4CX800 GU74B Tube Tetrode Valve Amplifier Amateur Radio.


Project Tsunami. Burkhard, DF5XV, www. The live weight of this PA amounts to 1. Burkhard has an official permission of the BNA for 20 KW on shortwave for broadcast, although not for ham radio. Such enormous values of transmitting power challenge even the creativity of an experienced high frequency engineer. Well, three years ago, the of this article placed a bet against Burkhard to build a power amplified with more than half the output power of the VK20 in SSB mode, yet would fit the trunk of a compact car as well as a manageable weight. So the race was on!

Category: 4cx800 output

4cx800 amplifier how to

From the N4UQ e-mail archives. The characteristics of the tubes are very similar. These triode tubes are found mostly in grounded grid amplifiers. They use the same inexpensive socket. Only the filament voltage needs to be changed.

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4cx Measure the screen voltage starting v Control Grid Voltage and These triode tubes are found mostly in grounded grid amplifiers.

How to exchange the GU74b / 4CX800 tubes on your Alpha91b (Alpha99) Amplifier

Rodger Singley Mon, 27 Nov Skip to site navigation Press enter. Joe and Drakelist, You definitely should not be driving the grid current to excessive levels as this can easily damage the tube. A couple of thoughts: 1.

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If you cannot hear them, you cannot work them. So, before buying an amplifier, install the very best antenna system you can afford.

It finally happened… After a decade of reliable service, my Alpha91b amplifier broke. Most likely on its way to Spain one of the tubes broke. The first shock was big, but a few measurements confirmed that just the tubes were broken. In this blog post, I will share the knowledge I gained during debugging, commissioning, and breathing new life into the amplifier. Do not perform ANY work on your amplifier if you are not exactly sure what you are doing. Again if you are not sure, contact RF-concepts or your local dealer.

From the N4UQ e-mail archives. The characteristics of the tubes are very similar. These triode tubes are found mostly in grounded grid amplifiers.




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