Building K5LAD's 4-1000A Amplifier
I built this amplifier back in my younger days, back in the early 1970s. A check of my logbook shows that my first contact using the amplifier was with Gene - K5NYT in Tulsa on 3905 KHz on March 31, 1973. Since that time, I've made many contacts using it and this amplifier has always been a real benefit for my ham station. On numerous occasions, I've gotten requests from other hams, asking for a copy of the schematic or some other detail on my amplifier. The truth is, when I originally built the amplifier, I had no "official" schematic and different sections were on various scraps of paper. I always kept the scraps together in a folder but it was far from being an organized documentation package. Different sections of the circuit were taken from different places. When I found a part of a circuit I liked on some other published amplifier circuit, I borrowed it and incorporated it in my amplifier.
Finally, in 2008, some 35 years after building the amplifier, I decided to put together the scraps and get some sort of organization to my documentation. Using Microsoft Paint, during times of poor TV shows (and there were MANY) I drew up the schematics of the power supply section, the control section and the actual amplifier. I've tried to identify different pieces used in the project, often from the original bills of sale from the piece which I had also saved in the documentation folder. Some, however, are not identified completely, by either a commercial nomenclature or an actual value since I don't have that information available. If this amplifier ever breaks down, I'll get back inside and write down some of those unknowns. The problem is, however, this amplifier has many of the features of the Eveready bunny and just keeps going and going and going. When I built the amplifier originally, I did not deliberately build it for quick and easy disassembly so I've never decided to just sit down and take it apart to identify the innards of the beast. Some day, perhaps, but that activity is certainly not scheduled. If someone wanted to duplicate some of this amplifier, I think there is enough identified that it would not leave you too far out in left field. In particular, I'd like to be able to identify the values of the tuned circuit in the switched input of the amplifier but that's probably a several hour project and just not one I'm interesting in pursuing. Perhaps if I ever retire I'll have some time to do that............ Oh, oooops, I'm already retired. Oh well.........
First is the schematic of the amplifier. The amplifier cabinet was constructed from aluminum angle stock which was tapped to allow the shell of the amplifier to be attached with 10/32" by 3/4" binder head screws. The front panel was constructed from a commercial piece which was Bud PA-1109 Aluminum Panel (15 ¾x19x1/8) - Light gray textured. After all of the holes were drilled and machined into the front panel, the lettering was engraved into the aluminum and black paint placed in the engraved letters. The front panel was then belt-sanded to give it a nice smooth grain, then it was clear anodized to protect the surface. Now, after 35 years the front panel still looks as nice as it did the day I made the first contact with it. I was fortunate enough to have a good ham friend who owned a specialty machining shop and he took care of the engraving, sanding, and anodizing tasks. I don't recall what I paid for this service but it was worth every penny.
The inner chassis, made from a Bud chassis Bud AC-1428 - Chassis (15x17x4), had all the holes sealed and the squirrel-cage blower blew directly into this sealed unit. The chassis was totally pressurized and the only way the air could escape was through the Eimac air socket, past the tube filament pins to keep them cool, then with the help of the Pyrex tube chimney, past the tube's outer envelope, then past the aluminum-finned tube cap and out the top of the chimney and finally, out the top of amplifier via a nice round chrome 5" speaker cover. Even the rocker switches in the front were sealed so air could not escape around them. As I recall, I used quite a bit of RTV to seal every little nook and cranny.
The amplifier schematic has most of the components identified. The exception is in the input tuned circuit. Only one band is shown and even then, I did not have the values written down, at least on any note I had saved. The three larger meters used were a cheaper Philmore 0-1 ma meters but were available at my ham store when I built the amplifier, really looked nice, and an especially nice thing -- they all matched. The scales were hand drawn to match the new scales but I have recently found a program which allows the user to make a really nice, customized and colorized scales so that project is on my list. As closely as I can recall, here's a list of parts used in the amplifier section Click on this link. Note that there are some prices beside some of the pieces and it should be noted that these come from the scraps of paper and the original bills. Remember that this was in the early 1970s and that was back when you were buying gasoline for less than 99 cents a gallon............ assuming that the reader was even born during this time. Ah, the good ole days.... where have they gone???????
Note that the amplifier has a smaller output meter with a potentiometer adjustment just for maximum and quickly tuning the amplifier. The amplifier also has a built-in ALC circuit to allow a negative-going voltage back to any transceiver which needs that. I could not find any scraps of paper with an ALC circuit shown so that's another one that I'll need to reverse engineer whenever I open the amplifier up. If you're using one of the typical ham 100 watt output transceivers, you don't need to worry about overdriving this amplifier.
Here's the power supply schematic:
A list of parts for the power supply is also available by clicking this link. I wish I could also tell the reader where I got the parts I used so they might be able to find the same for themselves but it's just been too long since I found these parts.
And here's the wiring used to control both the amplifier and the power supply:
The four switches, used in the control circuit are SPDT rocker switches with a translucent body and a neon bulb and series resistor behind it. When the switch is in the ON position, the rocker switch body is lighted. This makes a nice feature.
The FIL. switch is wired so that it cannot apply power to the tube filament unless the BLOWER switch is also on. Since the tube filament takes 7.5 volts at 21 amps, that's a lot of heat to dissipate, even if the high voltage is turned off. The 4-1000A has an instant-on filament so there is no need to have a delay between powering the filament and applying the high voltage.
The H.V. switch controls the 117 volt AC voltage going to the power supply cabinet through the Remote/Local switch on the front of the power supply box. With current cabling, the power supply box can be located 8 to 10 feet away from the amplifier, the user has complete control from the front of the amplifier panel.
The RELAY switch could also be called a "Stand-by" switch since it allows the amplifier to be fully powered up, both filament and high voltage, but with this switch in the off position, the transceiver will bypass the amplifier and feed through without amplification. In this stand-by position, the tube is biased off to draw minimum plate current with no drive.
The pictures, and the descriptions shown below them, are from the power supply section. I'd like to say that I build all of my equipment so that it looks beautiful and could be used as an example for all, however, it's just "ain't so." I even considered leaving out the pictures of my power supply construction so you might think that since it works so well, it must be a picture of perfection. Ha! It is what it is and it works well and every time so, what the heck!?!
NOTE: At one time, I sat down and created a Troubleshooting Chart for my 4-1000A amplifier. It might not be useful to others but I will include it as part of my documentation package. Click here to display this Troubleshooting Chart.
Written August 13, 2008
Updated 01/18/09 01:41 AM