AL811 AL811H Ameritron Critical Safety Mods 

Where did you find the build date on the amp?

Penta has never treated Ameritron right or other people. In the 1980's they sold Ameritron, when I was GM, a batch of 8877's that turned out to washed and relabeled defective Eimac returns. We learned this because some of the serial numbers matched defective Eimac tubes we had sent back to Eimac. Years later, after MFJ bought Ameritron, they did the very same thing on other tubes. In neither case, even years apart, was anyone refunded. If you search the owner's name you can find and read the judicial history for yourself.

@@Jerrythenerdful Most of my tubes came from RFparts. I never had a problem yet. love the 3-500ZG RF parts ladled tubes. Many friend's run them and they last.

@@Jerrythenerdful very interesting information going back to the 80s and showed a pattern of common practice

I would remove any MOV's. They are a source of future problems. When they fail, they fail shorted or partly shorted. I find a lot of MFJ products with unsoldered or poorly soldered connections. I estimate that maybe one out of every five to ten 811 amps I see have one or more connections inside that were never soldered but still working! You can get away with this in tube amplifiers more than solid state, but it would sure be better if they inspected a bit better.

Thank you, I'm not sure I deserve that though. Sounds like you had an fun car. I love people who have the unusual or uncommon cars!

Thank you! We were desperate to protect radios back around 1990. At that time GDT's were a lot less common and much more costly, plus MFJ had them in stock, so we used MOV's. The protection changes evolved over time. That basic amp design is over 30 years old. It probably needs a whole rework.

I replace MOV's quite often. power surge is very common hear. I put bigger ones in. replace V130LA10 with LA20 Etc. I buy 100 at a time. Eaton has new blue Hybrid MOV that has better life. RU-vid video under EATON . have not got them yet. in the AMP for filament protection GDT's much faster and last longer. 73's

Hi Eddie, I'm in the house now so I can't see work emails. The only unreliable bleeders are the sand color ones. My KS has 500 volt longer life capacitors, plus they are closer to the ideal size. You really do not want to upsize the capacitance. It is already way larger than it needs with the original 220uF, and I think MFJ went bigger still. It really needs more voltage, not more capacitance. Let me know what you need and I can throw it in the box. In the three tube version, a direct 572B swap is good. Just plug them in. Recently I discovered MFJ downsized the fan airflow. I had no idea they did that. The Cooltron China fan flows about 8 CFM of air and the amp really needs at least twice that, ideally around three times that if you run carrier or digital modes. I had no idea they cut back on cooling until I saw a fairly new amp with thermal damage inside. Then I checked airflow because it felt light almost no air movement. The very minimum airflow with cabinet on should be 15 CFM with three 811 tubes.

It requires at least one 200 ohm swamping resistor to be stable. The Collins 30L-1 is another example of a non-neutralized amp.

another reason to not buy that amp

Yes, absolutely. At least as much as it is practical in an amplifier, the grids are best going directly to ground or bypassed at the socket with a low impedance path to chassis. The exception to this is "neutralizing" a single band VHF amplifier by series tuning the grid. If there is an exception to this I would like to have a conversation as to what the exception might be.

Yes on all grounded grid amps I do every heathkit amp I work on they picked this procedure up from Collins radio that was one of the bid design flaws Collins did. If its a grounded grid amp ground the grids right to ground as short as a lead as possible. If this affects the grid metering section of the amp this redesign the metering section.

Almost all of these mods are done in newer production amps.

@@Jerrythenerdful Thank you. I saw some of the mods inspecting this one. Works great so far.

No I do not follow you. 1.) The B+ plate arc forms a quick rising pulse with a very wide spectrum content. It tries to elevate the grid and the filament off near-chassis level to 1500 volts B+. 2.) The large filament choke is a high impedance for fast rising pulses, so it blocks the higher frequency energy in pulses from the transformer filament line. Only the lower frequency sustained energy makes it there. 3.) The fast rising pulse energy above lower frequencies makes it through the parallel .01uF caps, and through the tuned input, to the radio port (if relays are closed). 4.) That pulse bangs the radio input just like any ESD. Some radios take this OK, some radios are sensitive to it. Sometimes this knocks a final out, sometimes it damages the radio output bridge diode, sometimes a receiver input part. It all depends when and how hard the pulse hits and how sensitive the radio is. ICOM for example blames this on ALC at times, and they also have blamed this damage on lack of a relay line isolation device. The MOV's cannot be used on RF lines. They can only be used on the low frequency stuff, so they are not fully effective. The MOV's have also turned out to create a secondary problem. They sometimes fail shorted. This biases the tubes on all the time. The MOV's should be removed, three GDT's installed. If the grids float on resistors the grids should be directly grounded. ALL of this is factory production changes determined by years of field failure experience and testing here at my place.

mac p I do not follow you, either??

I recall your name and e-mailing you. If you can't see my reply check your spam folder. If you use g-mail it is unlikely I can get a message to you.

The ARB only protects the relay jack from spikes from the relay. It has nothing to do with tube arc protection. I can repair these amps, I do a lot of them, but I eventually want to phase out of service and concentrate on products. www.ctrengineeringinc.com/

I have not seen any email from you. My email for orders is orders@ctrengineeringinc.com Make sure the "inc" is in there.

@@Jerrythenerdful I got your reply in email and placed the order yesterday. I'm excited to get the old 811 back in action and up to date. Thanks in advance!

Sorry, but that is not true. The issue is the slew rate of the pulse. It passes right through a series capacitor as it charges the capacitors. This is not slow rise dc, it is a sharp pulse.

You know the history by rumor I suppose. I am not sure how you would know it, but I know the history by being involved with the trouble when Ameritron decides it is critical. The problems with tube faults damaging radios is the reason there have been a variety of changes in these amps over the years. At first MOV's were installed, along with a large capacitor to absorb energy. The MOV's help mitigate damage, but are unreliable in the field. After a few hard arcs they either fail sorted or sometimes fail open. Tube shorts in these amplifiers are relatively common. In a significant percentage of these cases, a radio is damaged. The damage is sometimes blamed on ALC voltage or on relay line voltage. It is best that people add GDT's and bring the amplifier up to current spec's.

If I'm understand the information on his web site correctly, the guy who made this video is the guy who actually designed the amp! And basically, what he's saying is that if you have an older version of the amp that there are modifications you can make to protect your exciter and your amp from being damaged by faulty tubes.

I know someone who lost 2 amplifiers and a radio by exactly this failure mode. An AL-80A, which he ended up giving to me. I rebuilt it and now use it every day, and an AL-80B which damaged his radio. He ended up selling that one, unrepaired. Had there been at least the GDTs, a simple tube swap might have put the amps back on the air. Of course if they did have the GDTs, I wouldn't have my wonderful AL-80A, made before MFJ owned Ameritron.

It is a good inexpensive amplifier, which was the targeted design. It just needs updates. It is an old design I did from back around 1990.