10/12 Meter Modification Instructions. AL (not A or B). The AL needs a kit to modify for 10/12 Meters. Write to us for details. All other units DO NOT require. Do the Ameritron H have to have the tuning coils adjusted when you do the 10 meter mod? I have not done the mod on my H and. the al & h mod is SIMPLE. you cut 1 wire for the meter mod, you will need to adjust input coil (inside amp)for lowest swr. if you do.
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The modern components are rated to deliver reliable, effective HF communications power levels if operated within their specifications. The ALH has the essential design elements for a clean, stable signal. The lowest priced amplifier, the three tube AL, lacks neutralization and some other important design features that are included in the ALH.
I would encourage you to spend the extra money to get the ALH instead of the 3 tube model, if those were your options. There are certain design measures in the W8JI updates that protect the amplifier from damage if arcs occur. There are also reports on eham reviews of receiver front end destruction due to tube arcs getting back to the transceiver. This amp is not the only grounded grid tube amp that needs this protection; it has become a problem, due to inferior tubes of today.
If you have an older model ALH which does not have these design updates, I urge you to install them, or send the amp back to Ameritron for rework to current specs.
This web page is a detailed step by step supplement to the W8JI instructions. I also install an arc protect fuse and resistor in the HV lead. This measure is standard in Ameritron higher priced amplifiers, and a common mod to update older amps like the Heathkit SB I installed similar modifications on my SB Installation of the ohm swamping resistor is “optional”, according to the W8JI instructions. I put it in, after we encountered a clicking noise in the receiver in amplifier standby mode.
The ohm resistor does not have a DC path to the cathode circuit, so I did not understand how it would improve the cut off bias situation. The only purpose I could see it serving was to terminate the input circuit by resistive loading, to reduce a tendency to break into a burst of RF oscillation due to the tubes not being properly biased OFF.
The burst of oscillation is very brief, and no current is indicated on the plate meter. It automatically extinguishes when the arc suppressors fire, upsetting the bias. W8JI states that in some cases the clicking happens on different bands with varying plate and loading settings. This is the classic definition of instability.
Otherwise, the plate and load or band settings would be irrelevant.
Ameritron ALH 10m Mod | QRZ Forums
It is not surprising, since if the tubes exhibit sufficient gain, and there are no resistive terminations on either the input or the output, oscillation may occur, even in a well designed amp.
In the meteg mode, neither the input nor the output of the amplifier are terminated, and the plate supply voltage is ON. If the tubes are not actively driven into cut off no gain the amplifier, even though it is neutralized, will possibly oscillate even though it is neutralized. Under normal conditions with the relay closed, the tubes are connected to a transceiver on the input and an antenna on the output, and it is stable.
The ohm resistor did not cure the mos problem in our case. It is supposed to prevent a clicking mster in the receiver while in standby; that may or may not work for you. The schematics in the most moda releases on the Ameritron web site do not show either this mod, or the other W8JI mod which I did not try which uses a DC bias derived from the High Voltage supply to drive the tubes into cutoff no plate current.
The gas tubes fire at VDC, which accompanies the clicking noise. Otherwise, I speculate that residual gas in the tubes is driving the cathode voltage above that cut off voltage value otherwise the arc suppressors would not fire. Since neither of the mods W8JI suggested are installed in current production models, I did not proceed further.
Apparently they select tubes for proper operation in their amps, since eham reviews does not note this problem. The new tubes used in the rebuild worked fine otherwise, but they were not from RF Parts or Ameritron. Possibly your results will be better, if you use tubes from those suppliers. I cannot imagine users of new ALH amplifiers not complaining about the clicking, so Ameritron must select the tubes for cut off characteristics as well as burning them metfr to reduce the arcing problem with new Chinese tubes.
The W8JI ohm resistor mod increases the drive power from about 40 watts to 45 watts on 80, 40, and 20 meters. Installing a pair of ohm resistors requires redesign of the input matching network, as A,eritron notes. Other bands are proportionate in drive demands. You must avoid drilling a mounting hole that damages the neutralizing transformer.
You must be careful to avoid pinching the wires from the filament choke under one of the standoffs when reinstalling the sub chassis. There are other details, but first you must have the W8JI instructions.
Go to the W8JI page and print these pages out: Here is the list of parts and sources to meteer, with approximate prices: Do not substitute on the P style resistor.
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. There is a lot of internet hype about parasitic suppressor design. 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 mete 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 ameriitron 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 zmeritron 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 meeter 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.
Ameritron AL-811H 10m Mod
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 metwr the power supply PC board. W8JI does not include these steps, but the tubes are expensive.
Ameritron Als-600 10 Meter Mod Kit HF
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 ameritton to the thin insulation coating on the wires.
Ameritron Als 10 Meter Mod Kit HF | eBay
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: 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. TWO from each filament lead to ground. 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.