Ameritron Company. INCLUDES 10 METERS, 200V. $5,099.95 Ameritron. $5,099.95 Details. Page 1 of 11 MFJ Enterprises Inc Our Brands: Important. People of Ameritron are not keen in flawless drawing understandable diagrams. They are even inconsistent when drafting the components. Of the same device circulates different schematics! To more understand the track of the meters I drew the schematic differently. Now one can see how a rcing in the tube blows the 50 Ohm resistor and partly.

The Ameritron AL-811 10 meter mod is simple to do if you have just a little mechanical ability.

Now that the FCC have rolled back or removed the ten meter ban on amplifiers. Companies are selling them so it should be safe to share this.

Ameritron AL-811 10 Meter Mod

Modifying this amplifier for 10/12 meters, this use to require sending a copy of your license to Ameritron. Use this link Ameritron requests. Then they would send you directions. I recommend you do that now, especially if it is a new amp. If you have not bought it yet you may want to ask if they can do it for you. Their directions will not ruin the warranty.

1. Take off the window on the bake panel and see if you can see the green wire. If not then take out the cover screws and remove the top. Locate the rear panel PC board and the AUX tuning coil from the rear panel.
2. Looking down along the rear you should see the green wire connected from the PC board to the AUX tuned input coil as shown in the diagram. Cut the green wire and make sure it will not touch or go to ground.
3. Replace the window or cover and screws.

In some cases a high SWR may occur at the amplifier input. You will have to adjust the AUX tuned-input circuit slug with a plastic 0.1” hex T.V. tuning tool.

Put the tuning tool in place, tune the amplifier and tune for the lowest SWR while transmitting. Ameritron amps usually come pre-set for 10m (AUX tuning).

You may use 12 meters more than 10 and want to tune it for better performance. Re-tune the slug for lowest SWR in the middle of the 12 meter band. Or you could compromise the match, setting it for halfway between the 10m dip and the 12m dip. This will make it work on on both bands.

Watch the grid drive while doing this with the 811A tubes. They do not like to be over driven over driven.

This easy Ameritron AL-811 10 meter mod will have you talking on 10 and 12 meters soon, Happy DXing.

The Ameritron AL-811H is an attractive choice as an entry level amplifier for the low budget amateur operator. The modern components are rated to deliver reliable, effective HF communications power levels if operated within their specifications. The AL-811H has the essential design elements for a clean, stable signal. The lowest priced amplifier, the three tube AL-811, lacks neutralization and some other important design features that are included in the AL-811H. I would encourage you to spend the extra money to get the AL-811H 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 AL-811H 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-200. I installed similar modifications on my SB-200.

Installation of the 200 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 200 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. 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 standby 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 200 ohm resistor did not cure the clicking problem in our case. It is supposed to prevent a clicking noise in the receiver while in standby; that may or may not work for you. The schematics in the most recent 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 150 VDC, which accompanies the clicking noise. The bias in the W8JI high voltage resistor bias mod is a bit above 50 VDC, but 150 VDC is apparently not sufficient to cut off the tubes. 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 AL-811H amplifiers not complaining about the clicking, so Ameritron must select the tubes for cut off characteristics as well as burning them in to reduce the arcing problem with new Chinese tubes. The W8JI 200 ohm resistor mod increases the drive power from about 40 watts to 45 watts on 80, 40, and 20 meters. Installing a pair of 200 ohm resistors requires redesign of the input matching network, as W8JI 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. Adding a B+ fuse and protection resistor is important, and NOT covered in the W8JI mods. There are other details, but first you must have the W8JI instructions. Go to the W8JI page and print these pages out:
https://www.w8ji.com/al811_important_modifications_changes.htm
https://www.w8ji.com/al811_update.htm

Then you are going to have to order some parts. Here is the list of parts and sources to order, with approximate prices:
RECOMMENDED SET OF FOUR GENUINE 811A TUBES, 100% TESTED AND GUARANTEED CETRON: $56 X 4 = $224https://www.rfparts.com/tubes/tubes-811a.html?p=1
OR (See discussion of W8JI on power rating of Chinese tubes more like non-A old 811s)
Ameritron 811A Replacement Power Tubes #380-0

Ameritron 10 Meter Mods Pdf Writer