Cheapest & Reliable 800 watt PEP Out Amp

Discussion in 'Amateur Radio Amplifiers' started by N8FVJ, Apr 9, 2019.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    3CX3000A7 is a great tube and has been used in a couple amateur radio amplifiers, including a big model by Henry (8K)

    It can often be found for lower cost than an 8877 but then you have to invest in a bigger filament transformer, socket and other stuff.
     
  2. K6LPM

    K6LPM Ham Member QRZ Page

    I will give you that, but the quality we really are discussing is bang for the buck reliability and cost of ownership.

    So let's put the convienence of no tune aside, that is not going to be an advantage with an ALS 600.

    So we will indeed like to have an antenna tuner with this amp because nobody operates resonant antennas with a flat 50 ohm impedance across everywhere they wish to operate.

    So we have the expense of a tuner. Remember that this isn't a full gallon amp and that there are a few sub kw qro tuners that are fairly affordable. Also the tuner is a one time expense that you will likely eventually own , no matter what amplifier you own.

    Even so it is still optional with the inconvience of running a true resonant antenna tuned for your frequency operation preference. Remember you can load your antenna at the feedpoint with a proper matching network. I have always preferred a gamma match to get me there....

    The other arguement about SS vs hollowstate and the inheirent imd characteristics, well we are talking the ALS 600 which does indeed operate from a cleaner 50v device, it may not be inhierently cleaner than a properly tuned specific tube, such as a 572 or 3 500z but the amp does in fact meet FCC requirements and does have the proper fixed filter networks that meet and maintain a minimum tolerance quite well.

    I know I have heard many mistuned and fried 811 tubes that have been continually pushed and won't die but should be euthanized because they splatter like ex-lax all over the place by the LID that thinks that they should glow a bit or doesn't recognize the blotchy orange plates as being the not so good end all. Heck if it ain't catastrophic right?

    For that fact you will hear that same splatter from 500z or 572 too. Just mistune the plate and ignore the grid and the amp is a splatter box. Maybe the s/s isn't such a bad thing after all. The appliance operator can't mistune it enough to qrm the service or services without the amp going tilt by default and saving everyone on the air from the misguided?

    BUT A BIG CON for the S/S amp is that the finals are indeed fragile compared to the tube. If it wasn't for the foldback and protection circuitry the cost of replacing finals could put this option on the bottom of the list . However, the protections work good and if you run a balanced 50 ohm antenna that is resonant you are ok , or you optionally have a fairly decent tuner that is rated to 600 watts you will be good. You could even work a 300 watt tuner if you are very kind and know your limitations and have a decent antenna system.

    Hopefully just in case the protection circuit foldsback first. Worse case you arc your tuner. You can still sell the arc'd tuner for the same price you paid used for it on QRZ..... JUST JOKING!
     
  3. K6LPM

    K6LPM Ham Member QRZ Page

    100watts in should just about get ya full legal out maybe? Provided ya have the power supply ? I know that the filament is like 90amps huh?
     
  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Arc your tuner and blast the ALS600 finals... just sayin'.
    I've seen a bit of this type of damage. Better to run a big enough tuna if you need one.
     
  5. K6GB

    K6GB XML Subscriber QRZ Page

    My attic is fully finished and insulated, I'd move the shack up there except there are no stairs.
     
  6. N8FVJ

    N8FVJ Ham Member QRZ Page

    Cetron 572B will last about 30 years with at least 25000 hours use. Posted at AM forum.
     
  7. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    LPM:

    First of all, I edited your post to include paragraphs so that it could actually be read. Remember, unlike some Internet sites, QRZ.com doesn't have real limitations on the size of the posts. Therefore, PLEASE use paragraphs to make your posts readable.

    All that aside: I agree that, if possible, antenna systems should be well matched and my antennas do meet, as is practically possible, this. However, at least for 40-meters, 80-meters, and 160-meters, it is difficult to get a good match over the entire band and, for all practical purposes, unless you use something like a T2FD antenna, which is very inefficient, impossible on 80-meters and 160-meters. I, too, like the gamma match for 20-meters through 10-meters. However, for VHF and UHF, I prefer to use a folded-dipole driven element that has a ratio of 2:1 of the diameter of opposite sides of the element. This makes for a feed-point impedance of right at 200-ohms. Then, a simple 4:1 coaxial cable balun provides an excellent match to 50-ohm coaxial cable.

    For 40-meters, and lower frequencies, a gamma match gets very difficult to implement especially with wire antennas. With multi-band antennas, a gamma match just doesn't work.

    Right now, I have 4-linear amplifiers for HF: a Heath HA-10 Warrior (4-each 811A tubes), Heath SB-200 (2-each 572B tubes that are Cetron plus a pair of Cetron tubes as spares), home-brew 160-meter amplifier (2-each GI-7bT tubes), and a Henry / Tempo 2001 (2-each 8874 tubes). I designed the 160-meter amplifier to be able to handle a pretty wide range of impedance and the 2001 uses a rotary inductor for plate tuning instead of the normal fixed tapped coil with variable capacitor plate tuning. The 2001 can handle a wide range of impedance as well. The Warrior and SB-200 cannot match as wide an impedance range as the other 2-amplifiers. However, both of those amplifiers have no problems with any of my antennas that are for the bands that those amplifiers cover.

    I doubt very much that I am going to purchase an antenna tuner. In the 60-years that I have been licensed, I have only owned 1 antenna tuner for transmitting (I did make a receiving tuner for my first Collins 75A-1 before I learned about using TV baluns to match the 300-ohm input to 50-ohm coaxial cable) and that was a Dentron 160-meter only tuner that I got in a trade deal. It was soon apparent that all of my transmitters could match my 160-meter antennas better without the tuner than with the tuner. Eventually, I traded off the Dentron.

    By the way, all of my amplifiers including the Warrior, which is right at 60-years old, and my Henry / Tempo 2001, which is over 45-years old, have the original tubes and both are still putting out full power! Yes, I do know how to tune an amplifier.

    Take it from me, no matter how "fool proof" an amplifier is supposed to be designed, there are still going to be a significant number of amateur radio operators that are going to find someway to circumvent that design. Poor quality signals are still going to happen. Remember, a linear amplifier is, by design, going to amplify whatever appears on the input and, if the driving signal is dirty, the output signal will also be dirty and at a much higher level. But, I sincerely believe that there are going to be operators who find some method of causing the amplifier to contribute additional spurious emissions besides what appears on the input.

    There are auto-tune devices that can match a very wide-range of impedance. Unfortunately, these devices are not inexpensive. In fact, the best of these devices, the ones that can match the widest range of impedance, are VERY expensive. An excellent example of one such device was the tuner included with the Collins 308-U20 amplifier. This was an amplifier, designed for the U.S. military, that covered 3 MHz to 30 MHz (continuous coverage with no band-switch), that could be driven to full power output with less than 100-watts, and had a minimum output of 20,000-watts.

    One day, here at the "new" Collins Radio Corporate headquarters in Richardson, Texas, a couple of Collins' technicians were testing the auto-tune function in a new 308-U20 amplifier. To do this testing, they laid a 100-foot piece of 12 gauge wire across one of the parking lots and connected one end to the 308-U20 amplifier. Using a frequency in the 4 MHz range, the test was started. The auto-tune function worked well well. However, because of the very high power, the end of the wire started burning and the wire started getting shorter. On a whim, the technicians decided to see how short the wire could become before the automatic shutdown of the amplifier would happen.

    Over about a half-hour period, the wire got shorter and shorter. Finally, when there was just under 3-feet of the wire remaining, the automatic shutdown happened. Such was a test that showed a very wide range of impedance matching. As a reminder of this test, for a number of months, there was a scorched line, in the parking lot, caused by the burning wire.

    You don't want to know what the 308-U20 cost new! At the time, I could have paid cash for my 2800 square-foot house in what was the "best" neighborhood in all of the north Dallas area (including suburbs) for what the amplifier cost the government. Rodger Staubach (Dallas Cowboys quarter-back) lived down the hill and around the corner when he was playing, politicians, television personalities (a local major television new anchor lived across the street from me), etc., were in this neighborhood. In fact, there are still a lot of similar personalities who live in the neighborhood located in Richardson, Texas.

    Solid-state amplifiers have definitely come a long way in recent years. However, at this time, tube-type amplifiers still have an advantage and it will take a while before the solid state amplifiers eventually "catch up" with the tube-type units.

    Glen, K9STH
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yeah....

    The 3CX3000A7 filament is 7.5V @ 51.5A and rated output power in AB2 RF GG service is 7.26kW with 4.8kV Ep and 2A Ip.

    My neighbor Charlie uses them all over the place in his amplifiers at ASI: http://www.ampsystems.com/asiprod-old.htm

    He worked for Henry before they decided to stop making tube type amplifiers many years ago; but right at the end, the Henry 8K Ultra was his. 8K Ultra outside:
    [​IMG]

    8K Ultra inside RF deck, top view:
    [​IMG]

    8K Ultra power supply, inside view:
    [​IMG]

    That amp could output >>2.5kW with a 100W exciter and just barely get warm doing so. With 200W drive, ~5kW PEP output power.

    Good tube. Charlie likes them a lot.
     
    K6LPM and KD2ACO like this.
  9. K6LPM

    K6LPM Ham Member QRZ Page

    Hi
    Glen, thanks for the editing and response. As I have said before, I greatly enjoy reading your posts.

    I wonder what a 308-U20 could be had for on the surplus market in this day and age?
    Are they still in service these days?

    I envision some sort of system being employed in some obscure makeshift embassy or provided to some secret clandestined regime in the middle East!

    Dont get me wrong, I do love tube type technologies. It just seems in my opinion that if someone was getting started putting together an HF station, the ALS-600 is going to be a great value.

    A great majority of stations are already using solid state transcievers. A modest solid state amplifier for these types of stations make sense. MFJ makes several inexpensive manual tuners. Even those with roller inductors.

    Although not a mandatory accessory, many stations have them. They obviously are a very popular accessory if you look at how vast the marketplace offerings are out there.

    For that fact, a tuner is a great home brew project for a ham to cut their teeth on. I am surprised we don't see a huge amount of published tuner projects.

    For a more sophisticated station it is hard to argue the value in a tube amplifier. Especially given the fact that the prices on big tube amps continue to drop to bargain levels. No better time to buy that old dream Alpha or Henry console amps. Great deals on those big tube, big iron full duty amps these days...

    Of course if you are avid homebrewer you can purchase a handful of LDMOS devices for under five or six hundred bucks and have a start at building your own Kalifornia Kilowatt!
     
    Last edited: Apr 25, 2019
  10. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    I have no idea as to how many of the old Collins 208 and 308 series amplifiers are still in use. I suspect that there are a fair number. These amplifiers were normally installed in the communications "huts" that were then installed on military trucks. Most of these huts were being built here, at the Richardson plant, and the communications equipment had to be "checked out" before the huts were delivered to the military. There were large generators towed behind the truck on which the hut was installed.

    Unfortunately, the majority of problematic signals are now being generated by the all solid-state transceivers. Way too many operators, these days, do not receive any real training on how to use the equipment. Then, there have been mistakes in several transceiver manuals that actually increase the spurious signals if followed. When the person just reads the manual (and that is definitely NOT a "given"), and then follow the instructions, problems happen.

    There are definitely a number of operators who are of the fully clockwise turning of the controls and that almost every time causes many problems. Proper education, in the use of equipment, will greatly decrease the problems caused by misuse of the equipment. But, such education is just not emphasized if even available in the location. This really needs to change! Local clubs need to have an active program to make such education available and to urge every newcomer, in the area, to attend seminars on proper operating of the equipment as well as proper procedures, etc.

    Glen, K9STH

     
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