I had split this up in a few parts, so be sure and read all the parts to this article.
In a previous article about problems with linear amps I had such good response and many readers I am following up with another informative article.
For you newcomers and those old timers as well who are really thinking about purchasing a linear amplifier I have a few suggestions, some do’s and Don’ts in the process.
Let us start from the very beginning on this project and for those of you a little scared of a big amp perhaps I can get you over your fears.
Let us start with the shack, examine your operating position and determine if that big amp will sit on your operating position with out collapsing the table and all your gear into a heap of rubble. Most Linear amps on the market weight about 50 to 75 pounds, so do not put them on a card table for obvious reasons. Make sure you have a sturdy structure that will support the weight.
Next, you should have if you do not already have it and that is a 240AC line into your shack I have mine on a separate breaker, plus the rest of the gear on a separate breaker from my breaker box. I had a licensed electrician install the lines, if you are qualified to do this yourself have at it, but if you are not then contact a qualified, dependable and licensed Electrician.
We should take a look at your antennas at this time because we may have to make some changes with more efficient systems. If you have been content in dropping a long wire out the window and tuning it up with your antenna tuner, you may find this will not work with higher power. I would strongly suggest a resonant antenna for the band, or bands you plan to operate. It makes little sense to have a 1000 watts fed into an inefficient long wire, run the risk of damaging your amp with high swr and causing problems to your neighbors, then it is in having an efficient antenna with low SWR.
Determine where you are going to place your amp, then have the 240ac receptacle placed near the rear panel of the unit, you do not want to find out the cord will not reach the receptacle and have to replace the cord with a longer one. With that in mind we are now ready to place our order for that new amplifier and if you have found your best price, the model you want and the brand name you want then let’s consider placing the order.
I assume you have shopped around with various vendors for the best price, do not be stuck with one supplier, prices can vary as much as 20 percent. Plus some offer free shipping, others do not, some charge sales tax, others do not. Some offer service warranties and some do not. Get you best offer and let’s make that call, or e mail and have your credit card handy.
We make our call and place the order we wait about ten days to two weeks for in most instances three boxes to arrive at our front door. One large box containing the deck the smaller box the power transformer and the next box, or boxes containing the tubes and plate connector caps and suppressors. We will have some work to do when all this arrives.
Once that UPS or FEDX man brings those boxes you might want to find your self a dolly of some sort, even your kids wagon if you have to go a long distance to the ham shack will save your back. You will need some tools, a box cutter a ratchet wrench, and extender of at least six inches, plus a small blade screwdriver, a small Phillips screwdriver and a small set of Allen wrenches. Also, raid the kitchen and see if your XYL, or girl friend has a spare cup cake pan, or a small pot. If she says no, then find a drink cup from your favorite fast food place. Wash it out, let it dry and keep it handy.
Ok, Let’s go to work, open the big box and remove the deck, if you have room on your operating table to set the deck great, if not, you may have to work on the floor, or at another location, this is up to you. Find the instruction book and follow the directions as to what to do and when to do it. The first step will be to remove the cover on the deck that is the top cover; you recall I mentioned having a cup cake pan, pot, or drink cup? This is for the twenty four to thirty screws holding down the deck cover. Some screws are blade and some are Phillps plus the size of the screws is 1/4 inch. If you drop one, they have a nasty habit of blending into the carpet, so drop them all one by one in the pan or cup. Makes life a lot easier.
Set the cover aside we now want to install the power transformer, on Ameritron units the wires coming from the transformer are color coded and pictures are provided in the manual as to where these leads should be connected. You first need to mount the transformer, this is heavy so be careful moving it into place and not damage other components. It seems that three of the bolts are easy to access, but the fourth one is often very close to a shield preventing you from getting your fingers on the bolt, or nut. This is where the six-inch extender comes in handy; you can get in a tight place and do the job properly. Do not leave one nut and bolt off just because it is hard to access, get the job done right and use all four mounting holes with nuts and bolts. Some brands will have self-tapping holes for this mounting; others will use nuts and bolts.
Once you have the transformer in place time to connect it to where the leads will go, the manual will guide you, but if you are colorblind please get a friend who is not to assist you. There will be a high voltage winding, a primary, a filament connection, or in some cases a separate filament transformer. In the Alpha amps there is a Molex plug coming from the transformer and you match it up with another plug coming from control boards in the amp. Like this better, no chance of mistakes.
Be sure all leads are fastened to their destination securely, you do not have to over torque the screws but make sure the eyelets on the leads of the transformer are snug and not loose enough to move on the terminal strips, or connecting posts on the rectifier board.
Next step install the tube, or tubes depending on what model you purchased. Do not force the tube into the socket; note the keyway on the tube, or the pin arrangement if it does not have a key way. With a gentle hand insert the tubes making sure they are seated properly and go all the way down in the socket. At this point find the suppressors and plate cap connectors. You recall I mentioned a small set of Allen wrenches, some amps use an Allen head for the plate cap connectors, do not over torque these, they should be snug, but not overly tightened. This is dependent on who made the amp and the method of connection.
Insert them per instructions, now at this point you are ready to try the amp with the initial test. DO NOT PLUG IT IN JUST YET! Let’s put the cover on before we try anything, hopefully you put all those little screws in the cup, so now take them out one by one and reinstall them on the deck cover. Be sure and fit the cover in place do not at this time try and force the cover into place, it should go back in place the same way it came off the deck.
Once you have all the screws in place you are ready for the initial test, make sure at this time the top cover is in place, fitted correctly and is not forced into position. Next, make sure the power switch is in the OFF position, the CW/SSB switch is in CW and the standby/operate switch is in standby. Some models will not have all the mentioned switches, but act accordingly to fit the model you have in front of you.
Plug in the power cord, Nothing should happen, your are ready to proceed. Step 1 throw the power switch, if have a pair of 3-500z tubes they will light up and the plate voltage will appear. You should be able to look down through the perforated lid and see if both tubes have filament voltage. They should be lit up; if you have a ceramic tube such as 3CX 1500, or 4CX 1000 you cannot see the filaments. Plus you may not have any plate voltage until the tube cathode reaches a certain temperature. This normally takes about three minutes. Let’s assume you have glass tubes for the first phase and we will cover the ceramic tubes in the second phase.
