You are getting close. It depends on what mode you will use. You would not want to load up to 80 watts (key down carrier) and then drop the power down to 50 watts and run CW. With CW your peak and average power is the same so the peak power will be 50 watts not 80 watts so you would be better off loading at 50 watts and not 80 watts. If you are running SSB and your peaks will be 80 watts and your average would be lower you would load at 80 watts regardless of what your average power might be because the amp must be loaded for the maximum peak so you do not get flat topping, splatter, etc. You would treat digital modes the same as CW. Whatever your radio can handle or whatever the amp can handle in that mode (whichever is the limiting factor) you will load at that level.
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You are getting close. It depends on what mode you will use. You would not want to load up to 80 watts (key down carrier) and then drop the power down to 50 watts and run CW. With CW your peak and average power is the same so the peak power will be 50 watts not 80 watts so you would be better off loading at 50 watts and not 80 watts. If you are running SSB and your peaks will be 80 watts and your average would be lower you would load at 80 watts regardless of what your average power might be because the amp must be loaded for the maximum peak so you do not get flat topping, splatter, etc. You would treat digital modes the same as CW. Whatever your radio can handle or whatever the amp can handle in that mode (whichever is the limiting factor) you will load at that level.
This is the root of my confusion. I have never seen anything or anyone reputable state this before. Even the ameritron tune up procedure says to reduce the cw drive to desired level after tuning to maximum exciter output or amplifier output.
It would not hurt to do that and there is nothing wrong with doing that assuming theory and actuality is 100% the same. In reality it's not and there will be a slight difference, maybe not enough to be concerned about, but you can conduct a simple test to see what the difference may be in your particular situation. If you have a fairly accurate wattmeter you can see. First, load up your amplifier using your maximum of 80 watts of drive. Now back the drive level down to 50 watts. Note the watt meter power. Now adjust your load and tune at that same 50 watts for a peak in output. Record that power. What is the difference? Does the power increase to a higher level after after re-tuning? If you see an increase of X watts, those X watts that you gained by re-tuning the tank circuit at 50 watts is proof that the amp could be better tuned. If the power goes lower after re-tuning then it proves wrong. See what happens and you decide.
It was brought to my attention that I seemed stupid, ignorant, drunk, or trolling about this subject. I assure you this is not my intent.
I admit I don't know much about amplifiers, and that is why I have to have some faith in those that have proven themselves on the subject. If Ameritron, Tom Rauch and virtually every tuning guide available agrees to tune for max, I'm going to have to follow their advice.
If anyone has a link to anything explaining why it is better to tune at reduced drive, I would love to see it.
I admit I don't know much about amplifiers, and that is why I have to have some faith in those that have proven themselves on the subject. If Ameritron, Tom Rauch and virtually every tuning guide available agrees to tune for max, I'm going to have to follow their advice.
If anyone has a link to anything explaining why it is better to tune at reduced drive, I would love to see it.
This is one of the subjects that I usually avoid. The internet and the ameritron manual makes this more complicated than it has to be. Tune the thing for max output for the drive level you will be using. If the grid and plate current are not excessive (see the manual) it's good to go. Tune up with a dead carrier equal to the max pep you will be putting into the amp and leave it alone. A single tone on ssb will work also. A whistle is not a single tone and is not steady.
If you tune up and then increase the drive from the radio you have an under coupled condition. Grid current will be high so the tubes can be damaged and the thing will splatter. If you want to increase the drive power all you need to do when you retune is adjust the load control and it should literally take less than a second.
If you tune up and then reduce drive from the radio the amplifier is over coupled. This isn't bad as long as you don't get stupid about it. Linearity is improved and grid current is lower. Just remember the more you over couple it the more the efficiency drops. Tuning up at 80 watts and reducing drive to 50 usually won't hurt anything. The efficiency will be low but it won't be an issue on ssb. A high duty cycle mode like AM the tubes will run hotter. Since the 811 doesn't have much plate dissipation to spare you want to run as efficiently as possible.
At the end of the day it's your money and tubes. Do what makes you feel good.
I am seeing why W8JI claims that tuning at a low or reduced drive is the most common tuning error.
I asked a question and accepted the answer until further research seriously contradicted that answer.
It seems very clear with very little room for honest misinterpretation . Don't shoot the messenger please.
Quotes from https://www.w8ji.com/loading_amplifier.htm
The most common amplifier tuning or loading error is adjusting an amplifier at low or reduced drive power as a last amplifier tuning step. When we load a radio or amplifier at reduced drive as a last tuning step, we establish that power level as the absolute ceiling for drive and output power. Final loading at reduced drive results in a loading control too-far meshed. This can cause arcing, splatter, and excessive grid current.
Ideally (if possible) we should make the final tuning and loading adjustments at or near maximum exciter drive power.
The last few tuning steps should always be:
- Load the amplifier to maximum obtainable output at full exciter drive (without exceeding amplifier short term overload ratings)
- After that, advance the loading control very slightly beyond that point (towards less capacitance).
No post that I read is telling you to tune up at reduced power and then increase drive. This is what w8ji warns against. I'm not disagreeing and you're still arguing. Tune up at whatever drive level you want but you can not exceed that level without readjusting the load.
As you increase drive the more the load control will have to be advanced. What w8ji is having you do is err on the side of caution to make sure the amplifier is not under coupled. The average ham doesn't have a clue how that magic box works so you have to give them instructions like you find in the ameritron manual.
Another reason ameritron has such a tuning procedure is because their advertised power is a bit much. Like the AL80b. If you want a kilowatt out of a single 3-500 you better over couple it or the high grid current will damage the tube.
I peak the amplifier at the drive level I use and then slightly advanced the load as w8ji says to do. I use real tubes and have no reason to tune up at max output. That would far exceed legal limit on the amateur bands anyway so what's the point?
When you ask for advice, then start quoting your favorite tech.... or engineer, and ask us to prove him wrong about something that you dont understand you sound like another troll on this forum.
When you start a post with a silly comment designed to lead others to believe I am making ridiculous claims, it hard to believe you aren't just trolling me. Thank you.
Manuals are written so that maximum safety to the equipment is ensured. They don't have time to teach amplifiers 101 in the manual. That is something you learn on your own. As time goes on and you are a ham for "gold years" and beyond, you learn the finer points of operating and you expand on what manuals brush over. Just sayin'
543_Dallas is spot on with his information on tuning up a tube amplifier. I’ve owned Alpha, Ten Tec, Kenwood, Heath Kit, Palomar, Acom, Ameritron, Amp Supply and OM. My Alpha 91b was a pain to tune and for some reason preferred starting with the load control first instead of tune (sold it asap). My AL-1500 gets tuned with whatever exciter level I’m going to use. Thirty-five watts input generates 1500 plus output. Grid current is everything so the load gets adjusted accordingly and if that won’t bring grid current down I turn down the exciter level output. I’ve never used a two-tone or pulser, and do just fine using a CW tone or Ritty output. The nature of the beast is such that any change in exciter output typically requires tweaking the tune and load a smidge.
When switching bands if I don’t know the preset settings I start with only 20 watts input peaking my output. Then increase my exciter level to my desired level of output. Even knowing what my pre-settings are I would never start by driving my amplifier with full exciter output when changing bands, you’re just asking for trouble.
Brad
KE0XS
When switching bands if I don’t know the preset settings I start with only 20 watts input peaking my output. Then increase my exciter level to my desired level of output. Even knowing what my pre-settings are I would never start by driving my amplifier with full exciter output when changing bands, you’re just asking for trouble.
Brad
KE0XS
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Why is it that W8JI believes that many transceivers have a significant and hard to detect power/ALC overshoot when running reduced power? Is this true, or is he just crying wolf for no reason?
I will admit I was wrong when I thought it was tuning to max amplifier power. It is actually max exciter power that matters much more. It has been stated that an amp can be tuned at any reasonable power, and that seems true.
Few hams have the ability to detect a millisecond of power overshoot. If you can, there is no danger in tuning up at a reduced exciter output.
Tuning at max exciter output is best practice because of the danger of high voltage and arcs it can cause, not because they want to be complicated or think hams are stupid.
I will admit I was wrong when I thought it was tuning to max amplifier power. It is actually max exciter power that matters much more. It has been stated that an amp can be tuned at any reasonable power, and that seems true.
Few hams have the ability to detect a millisecond of power overshoot. If you can, there is no danger in tuning up at a reduced exciter output.
Tuning at max exciter output is best practice because of the danger of high voltage and arcs it can cause, not because they want to be complicated or think hams are stupid.