I sold MOV's for GE a few decades ago. These devices wear out a little with each voltage event applied. The more voltage along with the frequency of application determines their life time. They are also not narrowly spec,d. I am not surprised to hear of them being "unreliable" over time. One of the applications GE was touting them as lightening arrestors for housing. Attached in the electrical box. They were rated high enough to only age with over 250+ volts. With the electric company doing a good job with respect to voltage level the lasted a long time until the wore out via current leakage / getting hot. Appreciate the post as I picked up one of these third hand. Apparently the second person tended to loose tube sets frequently. The serial number is 12653 and I suspect it has the problems you have described that need to be eliminated. Great road map to follow
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. RUclips video under EATON . have not got them yet. in the AMP for filament protection GDT's much faster and last longer. 73's
This tear down really helped me out. I picked up a used "I am third owner" Al 811 H this morning. Supposedly never used so when I got home I took the cover off and applied AC. Only 3 tubes light up so I assumed a bad tube. After some probing around I find that one of the tube sockets has a open pin. So I had to go underneath the RF deck. Well one of the Filament's had never been soldered. The wire between two of the tube sockets was to short and though some solder was blobbed on the socket the wire didn't make connection at all. So a big thank you for this video. I need to re-glue about the top three windings on the plate coil. Of course I have no Q Dope. I have every thing else put back together but too tired to turn on tonight. This amp doesn't have most of the items you worry about. It does have one MOV on the back panel. That will stay in for now... Thanks again. Garry W8GMF
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.
Tom: Thanks for sharing your great knowledge about the 811 amp your truly one of the best ham sites on U- TUBE. About the cars I had a 1969 American Motors AMX 390 Cu/in V8 , 4speed , Hurst , posi ,Electric Blue with Black racing stripe ,Joel Rosen at Motion performance curved the distributor , it ran like a champ!!! John Boy Utah KJ7TBR need to get pics on QRZ, need to figure that one out ! Chow
Again, many people won't bother to thank someone for taking their time to share their knowledge. Or worse have to argue about everything. But thank for the education!
I just purchased a new 811H, and I'll be doing all the upgrades before using it. The workmanship seems to be fine, so I don't think there will be any major cleanup to do. I owned an 811H 15 years ago and had no issues running it exclusively on CW for several years. I never opened the case except to install the tubes. Many thanks for the video and upgrade kits. I'll probably order them soon.
Great video, learned a lot! I'm still classified as a "newbie" to electronics, but it's videos like these that go a long ways in teaching the skills needed for ham radio operations. Thank you Tom!!!
I can't not express how much knowledge I've learned from you over the years, sir. Nor can I thank you enough for the patience in which you teach, especially with "dummies" like me, or "newbies". 73 DE N4ZAW
The best improvements to these MFJ amplifiers are done with the relentless application of a good sledge hammer. After which they will give you no further trouble. Then you can move on to something good, like an SB-200.
Great video. I had an MOV fail on a 2019 AL-811H amp when I installed 4 new 572B Penta tubes. Supposedly these were matched and tested tubes. In any event I read and watched several of your articles and videos and I feel very confortable working on this amp. I think your work on explaining the 811H and other Ameritron amps are some of the best I have seen. You would have made a great teacher. Thank you! Hank K5HHQ.
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.
Picked up my 811 three tubers, from an Elmer friend for $400.00 built in 2008 ! I think it’s a good deal considering new ones are almost 1400 bucks . I will be getting a lot of your mods! My radio is a Kenwood TS-520s I think that 200 ohm input resistor will help me a lot and the gas discharge tubes. Thanks to choose the right CTR. JohnBoyUtah KJ7TBR 🇺🇸😎🎙📡
I have A 2000 AL 572 amp. never had any problems so far. I have many RUSSIA 572/B tubes working great. I have CETRON 811A and 572/B also marshal 811A and many china ones. even some 811H tubes. I know what you mean on some china 811A tubes flash over . I have several AL 811 series amps. had them pink bleeders go bad taking out a cap . That band rod on my 572 is brown fiber not a metal one. I haven't found any good china 6146B tubes but I got GE and ECG 6146W work super. MOV will go bad over time. EATON has some new blue Hybrid MOV replacements . mostly for line protection . GAS tubes are faster . great video . 73's
Thanks Tom for uploading this very informative video. I don't have an AL-811H, but some of the content is applicable to my amp. I have the following thoughts after watching it: 1) How is the 200 ohm value of the resistor that is added to work with the neutralizing transformer determined? (E.g., if one desires to have less effect on gain, would a lower resistance such as 100 ohms be appropriate?) 2) For some of us, a quick pictorial to illustrate the suggested circuit modification (such as the insertion of the 200 ohm resistor mentioned above) would be useful during the explanation of each modification. 3) Good point about the potential problem with loose/overlapping windings on the plate choke. The next time I have my amp open for maintenance, I plan to check the security of my plate choke windings.
Hi Tom, Ref: Ameritron AL811 amp not the H I just ordered 811KP and the 811R200K kits from you, well sent you the email for ordering.. Last year I changed the three 811s to three 572Bs by just swapping them out, was that ok or do I need something else? Last year I also put larger capacitors in the power supply, I didn’t change the bleeder resistors as your kit 811KS have. I also won’t need the 6A grid meter protection diode because it comes in the 811KP I ordered. Can I order or can you tell me what the resistors are? Thank you for a great website and videos you have made helping Hams. Eddie kj4fgi
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.
Very informative video as is all of the material you have posted on your website. Sharing your knowledge and expertise is a great help to the amateur community. Question: the problem as presented relates to the design degradation and manufacturing of 811A tubes. If I upgraded my amp (circa 2007 vintage) to 572B tubes will that mitigate the issue? Thanks, W6JAK.
What is the cause for an 811 (non H model) for the load tune to go to 0 when tuning up on 80M & 160M bands. There isn't enough load control to peak on these two bands.
Thank you for your service! Nobody seems to care about tube amp’s anymore! Shameful! Would love to see you publish a book or a paper on these mods with specific’s and put it on e-bay I would buy it in a heartbeat I will be getting a 2007 vintage Ameritron three tube 811 from an Elmer friend of mine. You video is extremely helpful! JohnBoyUtah KJ7TBR 😎🇺🇸🎙📡
Like the video, I happen to have an older, 23 year older 811...anyhow In prepping to remove all of the MOV's out of this al-811, exactly how many are there? and will be required in addition to the tube protection? The last simple question is what is the pin to pin location for the GDT's on the 811a's? Looking forward to your kit.
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.
200 ohm resistor. Okay, PLEASE give a part number & brand. For a GDT is this okay??: B88069X0880S102 Happy to purchase resistor and GDT's from you. CONSIDER doing this same type video on the Al-82 please as I own both and am sure others would appreciate it too. Thank you Tom
How would I know if my 811H requires this? I would guess that mine (I am 2nd owner) is about 5 years old. Is there a way to determine its age by the Serial # ? Am also using an ARB-704. Thanks.
Thanks for good portion of information. I have same unit in UK and i will do all modyfication You show on video. But i need to verifity its same PCB or mayby diffrent. Also i have some problem with power. I even install new 811 tubes and have only 430W . I cant find reason of this problem. Can You maybe give me some advice pls. ? Anywa its good video, i fix my old Yaesy 2100B based on Your knowelage.
Do you sell any upgrade kits for Ameritron AL-572? I'm waiting to be emailed back on the upgrade kits I need for my Ameritron AL-811H amplifier. I figured I'd order for both of my amplifiers. Thanks for that great video. KK4YLF
Oyie sounds like a scary and hairy job. Do you know if that's all the 811's like mine is marked inside 2008. I don't mind doing the work like that I'm just one who second guesses myself lol. Also here's a question isn't the ARB-704 supposed to protect you from that arching to the radio as well or just to help key up the amp ? And if someone like me wanted someone like you in the future to do the corrections to these amps would you do that? I love my 811 with 80 watts in I get out just fine. But of course im sure we all want to do what's best to protect our radios as well. 73's de N1GHI
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/
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.
@@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.
There have been tens of thousands of these amplifiers on the market for decades and this is the first I have ever heard of this. The possible occurrence of this happening is very rare and not worth the overkill effort.
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.
I sold MOV's for GE a few decades ago. These devices wear out a little with each voltage event applied. The more voltage along with the frequency of application determines their life time. They are also not narrowly spec,d.
I am not surprised to hear of them being "unreliable" over time. One of the applications GE was touting them as lightening arrestors for housing. Attached in the electrical box. They were rated high enough to only age with over 250+ volts. With the electric company doing a good job with respect to voltage level the lasted a long time until the wore out via current leakage / getting hot.
Appreciate the post as I picked up one of these third hand. Apparently the second person tended to loose tube sets frequently. The serial number is 12653 and I suspect it has the problems you have described that need to be eliminated. Great road map to follow
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. RUclips video under EATON . have not got them yet. in the AMP for filament protection GDT's much faster and last longer. 73's
Thanks Tom! What a great explanation on the different circuits of the amp and why the mods are so important. Please keep up the videos
This tear down really helped me out. I picked up a used "I am third owner" Al 811 H this morning. Supposedly never used so when I got home I took the cover off and applied AC. Only 3 tubes light up so I assumed a bad tube. After some probing around I find that one of the tube sockets has a open pin. So I had to go underneath the RF deck. Well one of the Filament's had never been soldered. The wire between two of the tube sockets was to short and though some solder was blobbed on the socket the wire didn't make connection at all. So a big thank you for this video. I need to re-glue about the top three windings on the plate coil. Of course I have no Q Dope. I have every thing else put back together but too tired to turn on tonight. This amp doesn't have most of the items you worry about. It does have one MOV on the back panel. That will stay in for now...
Thanks again. Garry W8GMF
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.
Tom: Thanks for sharing your great knowledge about the 811 amp your truly one of the best ham sites on U- TUBE. About the cars I had a 1969 American Motors AMX 390 Cu/in V8 , 4speed , Hurst , posi ,Electric Blue with Black racing stripe ,Joel Rosen at Motion performance curved the distributor , it ran like a champ!!! John Boy Utah KJ7TBR need to get pics on QRZ, need to figure that one out ! Chow
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!
Again, many people won't bother to thank someone for taking their time to share their knowledge. Or worse have to argue about everything. But thank for the education!
I just purchased a new 811H, and I'll be doing all the upgrades before using it. The workmanship seems to be fine, so I don't think there will be any major cleanup to do. I owned an 811H 15 years ago and had no issues running it exclusively on CW for several years. I never opened the case except to install the tubes. Many thanks for the video and upgrade kits. I'll probably order them soon.
Great video, learned a lot! I'm still classified as a "newbie" to electronics, but it's videos like these that go a long ways in teaching the skills needed for ham radio operations. Thank you Tom!!!
Outstanding video. Tom we appreciate you sharing your knowledge. So nice to see. Kevin
I can't not express how much knowledge I've learned from you over the years, sir. Nor can I thank you enough for the patience in which you teach, especially with "dummies" like me, or "newbies". 73 DE N4ZAW
The best improvements to these MFJ amplifiers are done with the relentless application of a good sledge hammer. After which they will give you no further trouble. Then you can move on to something good, like an SB-200.
Well this explains how my 811, LDG 600 and IC-7300 went on fire.
Just received my KP and KS kits today. I'll start doing the mods tomorrow when my shack (garage) is a little cooler.
Great video. I had an MOV fail on a 2019 AL-811H amp when I installed 4 new 572B Penta tubes. Supposedly these were matched and tested tubes. In any event I read and watched several of your articles and videos and I feel very confortable working on this amp. I think your work on explaining the 811H and other Ameritron amps are some of the best I have seen. You would have made a great teacher. Thank you! Hank K5HHQ.
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 just inherited a AL811 made in 1991 and your videos have been very useful. Many thanks.
Where did you find the build date on the amp?
Picked up my 811 three tubers, from an Elmer friend for $400.00 built in 2008 ! I think it’s a good deal considering new ones are almost 1400 bucks . I will be getting a lot of your mods! My radio is a Kenwood TS-520s I think that 200 ohm input resistor will help me a lot and the gas discharge tubes. Thanks to choose the right CTR. JohnBoyUtah KJ7TBR 🇺🇸😎🎙📡
I have A 2000 AL 572 amp. never had any problems so far. I have many RUSSIA 572/B tubes working great. I have CETRON 811A and 572/B also marshal 811A and many china ones. even some 811H tubes. I know what you mean on some china 811A tubes flash over . I have several AL 811 series amps. had them pink bleeders go bad taking out a cap . That band rod on my 572 is brown fiber not a metal one. I haven't found any good china 6146B tubes but I got GE and ECG 6146W work super. MOV will go bad over time. EATON has some new blue Hybrid MOV replacements . mostly for line protection . GAS tubes are faster . great video . 73's
such talent and useful information and only 961 subscribers, thank you Sir for the knowledge!
Thanks Tom for uploading this very informative video. I don't have an AL-811H, but some of the content is applicable to my amp.
I have the following thoughts after watching it:
1) How is the 200 ohm value of the resistor that is added to work with the neutralizing transformer determined? (E.g., if one desires to have less effect on gain, would a lower resistance such as 100 ohms be appropriate?)
2) For some of us, a quick pictorial to illustrate the suggested circuit modification (such as the insertion of the 200 ohm resistor mentioned above) would be useful during the explanation of each modification.
3) Good point about the potential problem with loose/overlapping windings on the plate choke. The next time I have my amp open for maintenance, I plan to check the security of my plate choke windings.
Hi Tom,
Ref: Ameritron AL811 amp not the H
I just ordered 811KP and the 811R200K kits from you, well sent you the email for ordering..
Last year I changed the three 811s to three 572Bs by just swapping them out, was that ok or do I need something else?
Last year I also put larger capacitors in the power supply, I didn’t change the bleeder resistors as your kit 811KS have.
I also won’t need the 6A grid meter protection diode because it comes in the 811KP I ordered. Can I order or can you tell me what the resistors are?
Thank you for a great website and videos you have made helping Hams.
Eddie kj4fgi
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.
Thank you Sir for sharing your knowledge!
Thanks Tom.
I am having trouble finding a video of how to install the mfj gop-100 on my al-811h.
Very informative video as is all of the material you have posted on your website. Sharing your knowledge and expertise is a great help to the amateur community. Question: the problem as presented relates to the design degradation and manufacturing of 811A tubes. If I upgraded my amp (circa 2007 vintage) to 572B tubes will that mitigate the issue? Thanks, W6JAK.
The 3 tube AL-811 (lacking neutralization) makes a great free running oscillator on 28mhz.
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
Good to see you on here! Thank you
Thanks Tom. It's good to someone gives a crap about quality.
What is the cause for an 811 (non H model) for the load tune to go to 0 when tuning up on 80M & 160M bands. There isn't enough load control to peak on these two bands.
Thank you for your service! Nobody seems to care about tube amp’s anymore! Shameful! Would love to see you publish a book or a paper on these mods with specific’s and put it on e-bay I would buy it in a heartbeat I will be getting a 2007 vintage Ameritron three tube 811 from an Elmer friend of mine. You video is extremely helpful! JohnBoyUtah KJ7TBR 😎🇺🇸🎙📡
Do you have a video for the AL811? Is there much difference in this mode for the Three tube AL811?
Like the video, I happen to have an older, 23 year older 811...anyhow
In prepping to remove all of the MOV's out of this al-811, exactly how many are there? and will be required in addition to the tube protection?
The last simple question is what is the pin to pin location for the GDT's on the 811a's?
Looking forward to your kit.
Great video and information. Many thanks. KB3NG
Great video!
Is the hard grounding of the grids pretty much applicable mod to all GG amps?
Many thanks...
de K4WRF
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.
Should I just simply remove the MOV’s? Just clip them? They don’t need replaced with anything else?
200 ohm resistor. Okay, PLEASE give a part number & brand. For a GDT is this okay??: B88069X0880S102 Happy to purchase resistor and GDT's from you. CONSIDER doing this same type video on the Al-82 please as I own both and am sure others would appreciate it too. Thank you Tom
Do you sell a DVD containing all of your AL811H updated? Are update kits prices current as of 01/31/22 before I order?
Front screw being the one next to the wafer , or further from the wafer! I.E front with reference to the front of the Amp or vice versa ????????
How would I know if my 811H requires this? I would guess that mine (I am 2nd owner) is about 5 years old. Is there a way to determine its age by the Serial # ? Am also using an ARB-704. Thanks.
Thanks for good portion of information. I have same unit in UK and i will do all modyfication You show on video. But i need to verifity its same PCB or mayby diffrent. Also i have some problem with power. I even install new 811 tubes and have only 430W . I cant find reason of this problem. Can You maybe give me some advice pls. ? Anywa its good video, i fix my old Yaesy 2100B based on Your knowelage.
Do you sell any upgrade kits for Ameritron AL-572? I'm waiting to be emailed back on the upgrade kits I need for my Ameritron AL-811H amplifier. I figured I'd order for both of my amplifiers. Thanks for that great video. KK4YLF
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.
Great instructions on the modifications. Would love to see the parts numbers for the GDT and resistor mounted under the tube chassis. Thank you KA4USN
Goooood Excelent
Oyie sounds like a scary and hairy job. Do you know if that's all the 811's like mine is marked inside 2008. I don't mind doing the work like that I'm just one who second guesses myself lol.
Also here's a question isn't the ARB-704 supposed to protect you from that arching to the radio as well or just to help key up the amp ?
And if someone like me wanted someone like you in the future to do the corrections to these amps would you do that?
I love my 811 with 80 watts in I get out just fine. But of course im sure we all want to do what's best to protect our radios as well.
73's de N1GHI
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/
Confused. You have blocking caps on the RF input to the tube and 50 volt MOVs on the filament line. Follow me?
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??
Ok..... I just ordered a brand new AL811H, delivery today 3/5/21 do these mods need to be done?
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.
I've sent emails about getting the parts kits - No reply as of this message 8/17/22. Are you still offering the kits? N6PRX
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!
actualy block capacitors on filament shoild be replaces with higher voktage values so they wont pass arc. Its simple
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.
There have been tens of thousands of these amplifiers on the market for decades and this is the first I have ever heard of this. The possible occurrence of this happening is very rare and not worth the overkill effort.
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.
and ground those grids..
so basically this amplifier sucks
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.