New metering schematic: Meter protection diode D16 is the unlabeled small black diode near C It protects the meters in the event of an arc. If D16 fails from an arc, the grid and plate current meters will track. The grid meter will no longer read grid current and the plate current meter will no longer read plate current.
|Published (Last):||5 March 2008|
|PDF File Size:||5.59 Mb|
|ePub File Size:||11.25 Mb|
|Price:||Free* [*Free Regsitration Required]|
Then you are going to have to order some parts. This is designed differently than a standard resistor, and will handle a surge current properly, without exploding.
That is why Ameritron puts them in their bigger amps. I got this part from one of those Ameritron parts lists. It is not standard on the economy amps in the AL series. I favor using the parts Ameritron and the designer, W8JI, recommend. They produce a lot of these amps. A ham without the engineering level test equipment who comes along afterwards with a speculative parasitic suppressor circuit design that works on one amplifier leaves me uneasy.
The Ameritron PC board listed above is an easy install with no questions about stability. Do not use smaller metric style fuse. This does not include labor, if you had to hire the work done. This assumes you did not uncover other problems during the rebuild. For instance, you may have to replace D16 and other components damaged from tube arcs. This is why I recommend people new to amateur radio just buy a new amp with a warranty.
If you already own an ALH, it is worth the cost of parts to rebuild it and bring it up to current factory specs, if the amp suits your needs. So now you have your parts and the W8JI pages above printed out. First thing I do before work is to take photos of the rig, so I can get it back together correctly. Click on any photo on this page to enlarge it. Note particularly the way the spacer and RF safety choke are assembled, and where the orange ceramic plate blocking condensers connect.
W8JI first removes the side bar between the front and rear panel. I have a small container with a lid to save all the screws removed, so they do not get lost. Then W8JI disconnects the orange ceramic disc plate blocking condensers.
See the orange pointer showing solder joint. Do not splash solder, damage the plate choke and neutralizing assembly, or do anything else silly. Loose screws, solder splashes, and metal drill shavings will fall places that cause the maximum damage. The bread always falls jelly side down. Then W8JI disconnects the RF choke that serves a safety function by grounding the output of the amplifier for DC in case certain components fail.
Be careful of the fine wire. I did not unsolder it, I just swung it out of the way. This keeps the front and rear switch wafers on the same band, in sync. It is much better to avoid this, but there is a procedure to align them if you mess it up.
Replacing the switch wafer is very tedious. Once you have the shaft removed, the next step is to remove the tubes and set them aside for safe keeping. Then disconnect the red high voltage wire from the power supply PC board. W8JI does not include these steps, but the tubes are expensive.
To install the Ohm 20 Watt resistor, you have to drill a hole. You MUST mount the resistor to a piece of metal for a heat sink. That is much easier with the whole subchassis completely removed. The vibration from drilling can damage the tubes. The high voltage wire is fragile, and needs to be disconnected anyway to install the fuse and glitch resistor.
This allows you to carefully rotate the tube socket sub chassis, laying it down on the main chassis, as shown in this photo. I disconnected the filament wires to avoid abrasion or damage to the thin insulation coating on the wires.
See the photos of the disconnection of the wires, as the orange pointer indicates. You can now see the resistors and capacitors from grid to ground used on the older ALH amplifiers.
These often burned out if the tube arcs. Some of these were replaced by the seller with inductive resistors, explaining why the Parasitic Choke Resistors also burned out. You will need to remove those components and replace them with a ground lug that attaches to the mounting screw nearest the grid pin of the tube. Once you have installed the ground lugs properly in contact with the tube socket grid pin, solder the lug directly to the grid pin.
W8JI arrows on his photo states: "Ground grids directly! Also, this procedure is simpler than the one recommended by PA0RFI, which requires that you remove and rotate all tube sockets degrees to get the grids pointing to the center, where he uses a wire to ground them at a central ground lug. This is a lot of work, and the sheet metal chassis is probably a better ground than a wire of any size. These normally do not conduct except in the case of an internal tube arc, which may occur in Chinese tubes.
You can see a close up of one of them, from the filament to the NEW grounding lug at the top of my photo. The second one is at the lower right, just out of view. Drill a hole just large enough for a mounting screw. I installed it differently from W8JI, because the terminal strip was mounted differently, and this resulted in the shortest lead length. Do not get rough with the leads, or there may be internal damage.
There is discussion about how many turns of wire are proper for the parasitic coils. Be sure you are using the latest configuration with fewer turns. The replacement choke is Ameritron I was able to salvage the plate choke in this amp because I had some unobtainium Q Dope, a special low loss polystyrene cement. Note some colored nail polishes use metallic or conductive ingredients.
If you are going to replace the HV power supply electrolytics, do it now. Be very careful to install them in the correct polarity. If they are 10 or 15 years old, it is better to do it now, even if they test good. With the screw connection style capacitors, it is very easy to make a mistake. Do not cut corners by changing only one failed capacitor.
They are all the same age. Do them ALL while you are in there. Use the parts from Ameritron to guarantee you have no mechanical problems with fit. If you are an expert, maybe Volt, longer life, degree capacitors could be substituted, but you will have to check for proper fit. Once you are certain that all modifications are done correctly, reconnect the filament wires.
Then you can reinstall the tube socket sub chassis back into the main chassis with the 8 screws you removed from the bottom of the amplifier. See how close they are to the metal standoff at the left? Also avoid damage to the red HV wire to the plate RF choke. Route it so that it can be reconnected to the Power Supply PC board, but do not reconnect it yet.
Now we are going beyond the W8JI updates. I also use this mod in my Heathkit SB amps. Do not use a junkbox resistor for this. I took out the other support brace after I marked the location for the mounting hole to drill it.
This prevents metal chips falling into the amplifier. I fabricated a small support from some bare G PC board for the fuse and resistors. First, I removed the junk box resistor kludge the seller had installed. The fuse protects the amp if the tubes arc. The resistor limits the rise time of the current from the capacitor bank into the arc. This gives the fuse time to act. It is not a guaranteed protection, but in most cases it increases your chances of amplifier survival by limiting the energy stored in the capacitors, which discharges through the tube arc.
In combination with the W8JI recommended mods, it all adds up. If you apply RF drive by transmitting, the grids will see that, with NO plate current.
This will result in excessive grid current. If you do not detect this immediately, the tubes will be permanently damaged. Watch your meters while transmitting. As long as you are attentive, this modification affords some further protection beyond the W8JI mods. I am obsessive about proper methodical test procedure order.
If you prefer a "smoke test", do it the expensive way. You should now see normal power supply voltage on the panel meter. Turn the amp OFF. Just to be safe, short them to ground.
If you got a capacitor in backwards while rebuilding the power supply, it will show up here, without involving the new tubes.
AMERITRON AL-811H Instruction Manual
Time Owned: more than 12 months. Well, the Ameritron ALH is not as inexpensive as shown at the top of the page eHam really needs to go in and edit some of the review header material , now being over a thousand dollars. But the ALH is still a tremendous bargain for a tube amp capable of around watts or a bit more a realistic figure, though the amp is advertised as having watt capability. I figured sticking with watts would keep relations with the neighbors on a friendly basis.
Ameritron Diagrams, Schematics, Service Manuals
Long Tube Life: The A tubes are long life, reliable transmitting tubes. The Grid Current meter provides a continuous reading of the A grid current to indicate proper loading of the Amplifier. Multi-voltage Heavy Duty Transformer: A unique "buck-boost" winding allows adjustment of primary voltages to match a wide range of line voltages centered on and volts. This versatile Ameritron feature allows the user to maintain optimum voltages on the tubes and other components to obtain maximum performance and life. Vernier Plate and Load Adjustments: Both tuning controls have vernier reduction drives for smooth tuning logging scales for accurate and rapid tune-up. Safety interlock: AC input power is removed from the transformer when the cover is removed. Never attempt to defeat this switch.
Stop electronic waste - fix it yourself