The AM Forum

The article "Why Not Give AM a Try" that appeared in February QST (p. 43) points out a not-so-well-known fact that will undoubtedly be overlooked by most readers.

Power level

Your 100 W SSB transceiver puts out 100 W PEP on SSB.  That is, at the peak of your voice envelope the  power output is 100 W, just as it can be 100 W with your key down on CW.  When you're not talking on SSB, your power output is 0 W.  The actual average output is typically less than 10W, depending on voice characteristics.

Of course, this is in reference to a good quality SSB voice signal that is not over-driving the rig or linear amp, and is not overly processed.

At the 10w level, on an amplifier capable of 100 watts peak, the amplitude of the signal voltage is running at just 31.6% of the amplifier's peak capability.  The amplifier is running at 1/10 of its peak power capability, and since power is a function of the square of signal voltage, the output voltage is 1/√10= 1/3.1623 = .316 or 31.6% of the peak voltage capability.

If you ever watched the analogue VU meters at a recording studio or broadcast station, you might have noticed that when a person is talking, the meter hovers at about the -10 VU or 30% modulation level, even though it may kick up towards 0 VU (100% modulation) on occasional peaks.  With music and other program material, it may run much higher.

So, the average power output level of a linear amplifier running SSB is actually less than the unmodulated carrier power of that same amplifier running AM at the same peak power level, and the SSB efficiency is averaging considerably less than when the amplifier is running AM.  The difference is not so obvious, because with AM, the carrier operates at a continuous 100% duty cycle, while with SSB, the power output is intermittent, running at a very low duty cycle, but the meters kick up to maximum on voice peaks while the meter stands still when the amplifier is operated properly on AM.

So much for the alleged "inefficiency" of a linear amplifier when it is used to run AM.

This means that at 1500 watts pep output, the average output power of a SSB transmitter should not exceed about 150 watts.

Therefore, the p.e.p. power limit bullshit penalised SSB just as much or even more so than it did AM, assuming that the SSB transmitter is run cleanly and properly.  Under the old DC input rule, a linear could be run up to where the meters indicated a kilowatt DC average input, with the peaks allowed to go as high as the headroom of the amplifier permitted. Amplifiers in the 50's-70's were universally touted in the ads as capable of "2000 watts pep input".  By running the linear at higher peak power, the clean SSB output power could be legally run considerably higher than it can under the present rules.

How many of the slopbucket linears you hear on the air these days are really operated within that power limitation?

Now, explain that to the next slopbucketeer you hear pissing 'n moaning that AM'ers run "illegal power".  

(Unfortunately, the concept will probably go right over his thick head.)

SSB makes up alot of deficiencies with the apparent increase in loudness at the other end, but half of that seems to be in the receiver.

There are many places in the older HB and other weighty tomes where the SSB voice wave is shown, and it is remarked that the avg power is 10% or so. Much is made of this, in an attempt to educate the SSB user that it is not the goal to merely crank out as much power as possible, but rather, go easy on it (if no kompressor is present) to avoid distortion.

So, since the PEP BS penalized SSB, the users of that mode would be well-served to work to get the KW DC rating back. But I think the FCC will never allow increased power. The PW/QRP horse is out of the barn. And like you say Don the slopbucket preferrers won't see the merits.

Operators did, and still do their best to make the most of the limits regardless of kind.

DC rating: increase PEP as much as possible.
AMers used to go way positive on peaks.
SSBers had free reign pretty much.
No one had to count drive watts going to a GG amp, or did they?

PEP rating: increase average power as much as possible.
AMers can boost the carrier and modulate downwards by inverting the speech waveform (up to a point)
SSBers just compress and compress.

Hey at least the FCC does not make us use "wall plug power" as a standard.

I think more hams are going to run QRO, at least for phone.  They will be driven to it by the number of RFI spewing appliances out there raising the noise level and making reception of <= 100 w. rigs with average antennas impossible.  I don't know anything about these qrp weak sig. modes -- maybe they can get through somehow.  We pretty much can't control all the garbage unfiltered gadgets out there, a lot like me can't afford to move to the country, and separate rx antennas and noise canceling boxes only go so far.   The one thing we can do, is up our tx power and antennas.  The new S3 is now S9.

Unfortunately, 10 % av. power only serves to make SSB ops run out and buy these speech processors, the latest being sold by Ten Tec, who's ad claims "almost 6 dB" increase in power.  I'm sure 8 out of 10 buyers will be ops who run these things with all knobs fully clockwise and of course they don't use scopes and have average reading watt meters.  Just wait until a lot of them buy that Ameritron solid state 1.2 kw amp.  It's all a recipe for unintelligibility, fan and saliva sounds.    :P

Rob

Darth Vader on steroids!

I doubt many operators limit power output no matter what mode they use.
I suspect the real power limit is what the station can run somewhat cleanly.

Taking the tube lineups of AM rigs and ssb amps I hear people using, I seriously doubt everyone is running their stuff at 20% power all the time.

Has anyone ever heard of anyone getting busted for running excess power if it was not something like 15,000 watts pep?

MY personal power limit is likely driven by the qrm I can generate in the hood, I don't want a big angry mob with pitchforks and torches outside the house....

I suspect the only people who really watch the power output are those running fragile expensive collectors items like the KW1...I bet no one straps one of those rigs anymore!

Brett

Brett and Rob, what you say is made even more salient by the fact that the FeeCee deleted the rule that used to require amateurs to possess accurate means for measuring transmitter power.

The old rule required accurate measuring instruments whenever the nominal DC input power exceeded 900 watts.  Johnston and his Private Radio Bureau crew knew full well that accurately measuring RF output power, especially peak power from SSB transmitters, would be beyond the means of many if not most amateurs, due to lack of appropriate measuring instruments and lack of knowledge of how to use them.  So, in the R & O of the power limit change, they made the incredible statement that (to paraphrase the exact wording) "amateurs may use means other than accurate measurement to determine their output power", and "amateurs are not required to measure their output power; they are merely required to comply with the rule".

And remember, this was written in 1983, when the overall technical expertise of the amateur radio community was at a substantially higher level than it is to-day, and just before the FCC moved amateur radio enforcement to near the bottom of their priority list.

On average vs: peak power for AM or SSB:

When I have an SSB pileup calling from Europe, assuming many guys are near the same strength, I usually hear the ones with the cleanest audio first. The ones with the processors (higher average audio with more distortion) and high pitched audio seem to blend in with each other. I've been an advocate of running NO processing and 2.8kc audio on ssb for a long time. But most do the opposite, of course, to get that last average watt out.

The strangest thing is that the boomy ESSB guys seem to stand out the most and get picked out easily. Proabaly cuz they are the only ones with the bassy voice tones to hear and everyone else sounds like white noise when combined.

The same goes for receiving. We need the cleanest receiver audio we can get to hear the weak ones. Obviously, any distortion detracts from the intelligibility.

On transmit, I watch my PEAK reading wattmeter. An AVERAGE reading wattmeter will hover much lower and cause us to have bad habits like overdriving the audio in many "clever" ways related to speaking.  I dont care if my average power is 10% or less, if that's what it takes for clean audio and intelligibilty. That's what counts to me. If the S meter is set on "fast," it will respond better to peaks anyway. That's the way I run it to keep the game-playing low.

Lately, I've been experimenting with breaking my ssb transmit audio into 6 bands.  No RF processing, just audio processing. We'll see how that works out soon.

On AM I prefer to do the opposite and run a higher density audio.  Most of the power is "wasted" on a carrier and a second sideband, so we need all the help we can get on AM.  But the same rules as above apply to AM - the cleaner the audio, the easier it will be to get through and be understood during marginal conditions.


T

For what it's worth:

I had a mail go-around with a deputy in Johnston's office when the power rules were changed back then.

He told me, "We're not going to endanger the safety of our field and enforcement people by having them attach meters to high voltage in a ham's equipment. We have peak reading wattmeters and that's the way we're going to do it from now on."

OK..

And then, there was the issue of people running the legal 1 KW DC input on AM and then running 400% positive peak modulation. Even the sidebanders were starting to figure that trick out..Run 10 KW PEP on sideband and inject 50 watts of carrier...It's still "AM" and 100 watts DC input, right? Turn that mic off and the meters are gonna read 100 watts DC input every time.

No wonder they changed the rule on power measurement. But this is a different issue than cutting AM back to 1,500 watts PEP, or 375 watts of 100% modulated carrier. They could have raised the legal limit to 3KW to 4 KW PEP for everyone, at the time, instead of disenfranchising AM.


Bill

Average rf power output would have adequately covered both of the FCC's issues.  

Undoubtedly, this was initially provoked by the W3PHL case in the late 50's.  But it took the FCC over 25 years before they decided it was a significant problem.

They managed to come up with satisfactory rules in Canada, that didn't reduce anyone's privileges.

But, I forgot.  Canadians are smarter than United States-ese.

How could that possibly work with SSB?  It did work with plate modulated AM because the average voltage of the modulation, consisting of unrectified alternating current, reads zero with a DC meter, and when superimposed on the DC from a power supply and read with a DC meter, only the DC voltage and current registers on the meter. With SSB, even with injected carrier, the DC input to the linear would still have increased tremendously when modulation was applied. W3PHL did it using double sideband, by running about 600 watts carrier with a slightly unbalanced high level balanced modulator, and applying 5 kw of audio as plate modulation.

I only use the power level necessary to maintain reliable contact.

'Course that takes into account the slopbucket, carrier, swisher and hola hola interference on any given night. ;D

<<I only use the power level necessary to maintain reliable contact.>>

Same here Bud, and my contacts are  very very  reliable, or as reliable as I can make them  ;D ;D

Here's the way I'm looking at it, Don.

The old rule was 1 KW DC input. Amps x volts, CW, no audio. Didn't matter is you were running CW, AM, FM or RTTY. There were no specifications as to how much your plate current could rise under modulation. There were no rules for maximum permissible positive modulation, either.

The FCC would have you key the transmitter and they'd read amps x volts on DC meters.

There was also no regulation concerning how much positive peak modulation you could run, OTOH, exceed -100% and you splatter, not 'Good Amateur Practice'.

If you had an SSB station, they'd have you transmit a CW carrier and read volts x amps on the final. They didn't measure your PEP. In fact, those running 50% efficient linear amplifiers were getting a worse deal than those running more efficient Class C.

So in my opinion, under the old rules, you could legally run 10 KW of sideband power (DSB or SSB) with a 50 watt carrier under CW conditions and be legal. All they read was your steady state power, NOT with any modulation applied. They never asked you to whistle into the mic while measuring DC input power, did they?

AM broadcasters had a different set of rules, you measured the antenna feedpoint impedance and you measured your RF current with a dead carrier to calculate your RF power. They never measured the RF current under modulation, the 120% max rule came along later. Couldn't do that with hams since we QSY and antenna Z is all over the place.

Remember the articles in the AM PX about how PEP was going to be measured if you were using open-wire feeders? LOL

That's my crack at it, but it's all a moot point now. ;-)

And don't forget, they are much happier then we are!

Sounding good last nite Don...

Brett

When I start modulating the shack lights I know it's turned up too high.  Time to reduce power.  ;)

Sounds to me like it's high time for a test case before the Commission. Anyone care to be the plaintiff in this class-action suit?

We can call Bill and Don/KYV as expert witnesses for the class.

Probably the best solution is to just run what you want within reason and be done with it. My informed feeling is that nearly everyone has been doing that for the last 20 years or so, at least since the new power regulations went into effect.

And Brett, I'm fairly certain that the majority of the guys running the KW-1s, Johnson Desktop Kilowatts, TMC GPT-750s, converted AM broadcast rigs, etc.,  think along the same lines.

Although it is interesting to debate the power ruling on a technical basis, it really is a dead horse issue at this point, with probably zero possibility of reversal or reconsideration by the Commission.

73,

Bruce

I like practical comments like yours, Bruce. The FCC has bigger fish to fry than the occasional QRO ham operator..As it should be.

Hi Bill,

Thanks for the positive comment.

I just noticed that you and I share the same classic quote by the late (and great) Arthur C. Clarke in our postings. It is a wonderful quote as you no doubt will agree, one of my all-time favorites, and of course one of the three laws of Clarke. Actually, the quote you and I share is known as Clarke's Third Law.

I don't want to hijack this thread, so if you want, we can discuss Mr. Clarke off-line or start a new thread.

Best 73,

Bruce

You'd love a house I did some electrical work on out in Palm Springs (CA) years ago. Huge place, 9-hole golf course in the back yard, part of the swimming pool came into the house under a glass wall. A classic example of true conspicuous consumption.

The feature that'd make it ideal for QRO ham ops was the electrical service. Each half of the house was supplied by a 600A, 3-phase service. NEC at the time prohibited more than one service entrance for a single-family dwelling. But, I guess money talks and the NEC walks, at least in Palm Springs.

Sure would be difficult to modulate the lights though...

ldb

I never noticed our duplication in tag lines before...I could switch to Law #1, which I like very well.

;-)

Hi Bill,

I think Mr. Clarke would be highly flattered if he knew we were both quoting his Third Law.

Please do not feel obligated in any way to change your quote, just because I use it as well!

Then again, variety is the spice of life. If you do decide to quote his First Law, we will now need someone to include Clarke's Second Law as their quotation.

Does anyone here on the board want to adopt Mr. Clarke's Second Law for their quote? Here it is:

"Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible".

73,

Bruce

What could they have possibly needed that much power for?
shelby

I have no idea. The entire roof of the house was ringed with 150W PAR floods about 20' apart, entire 9-hole golf course was lighted, long driveway and all walkways looked like airport runways, HVAC, probably walk-in reefers and freezers, etc. We worked on the roof lights, added a few receps and put in some special track lighting for a new painting and that was all. Didn't go into but about four rooms of the house. Never met anybody except the butler and a couple maids. Never even saw the owners. Don't know what was in the parts of the house we didn't see.

I will. just changed it to clarke's second law.

I get all these quaint laws from the old optimistic era confused... 
e.g. Clarks with Asimov's three Robetic laws, Drake's equation, SETI hopes, etc. 

Once upon a time we were going to Mars by 1970.

I will say one thing for Clark though.... we now have 30,000 geo-synchronous competing, yammering satellites, not to mention zillions of LEO's.

We've killed space with multiple gnats whilst letting the really significant stuff rot in the archives.

Additionally, one of the oldest sci-fi themes around is the civilization that never makes it off it's planet, just rots away, ossifies from it's own dumbing down and stagnant welfare states. 

Pick up some  Colliers issues of the early 50's to see  what we might have done.

Rick, it appears that this may well be coming to fruition at this point.

73,

Bruce

I think I could stuff a third 813 into the big rig.
2000 volts at 600 ma, about 900 watts carrier!
I think four would fit....

Brett

That has been in the rules from the very beginning of licensed amateur radio. It states that one must run the minimum power necessary to  carry on the desired communication. But what is the "desired communication"?  Does it imply a certain degree of signal quality and signal-to-noise ratio, or does it mean that both stations in a QSO are supposed to run right at the ragged edge of intelligibility?

Sky wave propagation is so fickle that about the only situation where that rule could be made to stick would be local cross-town communication via ground wave on MF or HF, or direct wave on VHF.

for me that would be crushing any stupid HAWWWW HAWWWW HWAWWWWW bleating ignoramus billy bob slopbucket that dared to try to qwirm me like a bug with my steel jawed maul.

Doesn't say much for the expertise of that FCC inspector.  I suppose he would have also told you that reflected power would kick back into your transmitter and cause the finals to run hot.  

Reflected power wouldn't have anything to do with nearby interference. It just means you are running your transmission line as tuned feeders and not as a flat feedline. With coax this might result in excessive feedline losses, but the reflected power in itself would not contribute to local interference.


Here is what they should have used: http://birdtechnologies.thomasnet.com/item/wattmeters-and-line-sections/portable-wattmeters/apm-16?&seo=110  The drawback is that they are not cheap, and are specified only down to 2 mHz.  I wonder if they would work satisfactorily on 1.8-2.0.


With 100% sine wave modulation, the thermocouple ammeter should kick up about 22.%.  With voice, the kick-up should be barely perceptible. The Bird 43 should not kick up at all, since it actually measures average rf voltage, with the scale simply calibrated in watts.  Average rf voltage should not change with modulation if there is no carrier shift. The APM-16 would kick up 50% with 100% sine wave modulation.

I wonder what that inspector would have done if you had been using a typical 1930's configuration consisting of a balanced antenna tuner, connected to the transmitter through clips directly to the tank coil, and feeding open wire tuned feeders with no 50Ω coax link anywhere in between.

Well, i think that the pep rules dont really make any sense at all, because the way i read them , then 1000 watts of carrier is legal for am, then when you modulate the carrier you end up with 1500 watts of peak power in your sidebands. But the 4 times the carrier is equal to the pep of the am signal does not make any sense to me because i remember reading a book once that explained how am works and this was the example that was given:

An amplifier has an input of 1000 watts. The plate voltage is 2000 volts and the plate current is 500 ma. When modulated fully , the modulator causes the input voltage and current to double (4000 volts at 1 amp). So it is saying that the peak input on modulation peaks is 4000 watts. so if the amplifier has a 70% efficiency, the carrier output is 700 watts and the peak would be 2800 watts.

It explains that in order for the modulator to develope this amount of peak power across the load of the plate circuit, the output of the modulator needs to be equal to half of the plate input of the amplifier. So the modulator is giving 500 watts of power to a final with an input power of 1000 watts, meaning the total power being delivered to the final is 1500 watts. Now if the amplifier is operating at 70% efficiency, the carrier output is still 700 watts (it is the same amplifer in the example above), but this time it is saying that the peak power of the sidebands is 70% of 500, or 350 watts, which means that the peak power of the carrier and sidebands combined is only 1050 watts.

Now if this makes any sense is it easy to see why the pep rules make regulating the power of an am signal difficult?
Shelby

Any power level is legal........ as long as you don't get caught!  ;)

Hey Mikey, I just watched VJB's and Bert's Timonium 2008 CD again and caught your mug. Just about as bad as mine.  ;D


"Caught"?  That implies guilt or intent.  Surely not us! (ahem.)

 If you don't drastically exceed ham norms of the present or even the past, it shouldn't take much of a lawyer to show a typical QRO AM operator is legal and trying 'very hard' to comply with the intent of the law, given the speciousness of the technical standards.  ;D.

 After all if enforcement is sporadic and can be shown to be such neat stuff as arbitrary and capricious, and you appear to, or do know what your talking about then the proof is on them.
....or I should hope so in what may still be a country based on fair law.
Operators like Don would be a good candidate for inspection, heh, heh.  He'd talk rings around a typical tech.  (Don't meant to be too patronizing Don, but facts are facts. Your good!)

So is any speed when you drive, as long as there is no cop in sight.

Tell me, what usually happens when you drive down the interstate and try to stay right at the posted speed limit?

Wonder how many of those who constantly piss 'n moan about "dem dar AM'ers runnin' illegal parr", conscientiously obey the posted speed limit 100% of the time when they drive.  Who is a greater detriment to the public interest, someone who speeds on the public highways, or some ham whose occasional voice peaks exceed the "legal limit"?

Yeah, and remember the 55 mph limit when virtually the whole country was a nation of outlaws? 

Well we still are; it's just that a 70mph limit is a bigger base, hence smaller ratio for the "5 to 10 over allowable." 

Most staties don't care if your over the limit somewhat unless it's the "end of the month" or you pass them.  They like to feel that they're special and king of the road.  The key is to treat them as such, but only formally when 'protocol' requires.

We've all been raised for endless generations to play the proper 'serf' on occasion. By now it's probably encoded in our genes.  ;D

Sometime ago I had hunting camp buddies who were Pa. state troopers along with some game wardens.  Great stories. 

It's who ya knows....    always has been, always will.

Yeah, around here it doesnt seem like the cops start to come out until the end of the month, then they are every where.

We complain that many SSB users, the new hams, etc don't build. Be thankful for that when it comes to amplifiers. It would be interesting to see the amp makers build in some circuitry that shuts the amp down or throttles it back when distortion is detected. With processor controlled amps, the user would have a hard time geting around that "feature".

or every 28 days.

You have to play sort of a guessing game.  If you follow the posted limit to the letter, people honk at you and try to run you off the road to get you out of their way.  You have to play a guessing game of how much over the limit to go to avoid both provoking road rage from other drivers and getting a ticket from the cops.

Rick said:
Except in VA where they clamp you to the letter.

Incidently Rick, that mug is getting pretty well worn, heh, heh.  ;)

Don said:
Don is correct. It is the same thing. I remember Rich Measures saying after building his 4CX10000 amp (or plywood box as he refered to it), "It isn't illegal to have a car that can do 200+ MPH."

most of these freakz are running a pair of russian GU 35's in their LINYARS at the same time talking smack about how wide amer's are.

..and that's a "fack" Derb, that's a fack.

"or every 28 days"
Good one Opcon....
Natural periods always take precedence.


..and I like the similarity to owning a Farrari.  Just because you have 500 hp, doesn't mean you drive everywhere at 200 mph.

But there is, perhaps, the excessive filament power required; "Friends of Coal, tm" being helped immensly.

Rick's Law # 62-56 A
Do not run filament power in excess of plate input power or your 1/Green.  ;D

For the more scientific of you,
The crossover point of a Gentleman AM'ers station is when filament power equals Plate input power.
   On special occasions (HM rally, etc.) you may be permitted to equal average output power.

There was fellow that used to run a pair of 8877's being pushed with his FT-1000D on AM. He sounded real good and his amp was computer controlled and very nicely constructed. I used to have his URL but I don't know what happened to it.  >:(

There you are.  8877's are very filament wattage friendly.  Indirectly heated oxide cathodes.  Too bad they're so expensive.  So the Filament 1/Green law is even harder to violate., urk.

..or do I have my recriprocals upside down? Help!

I think i am right on this but indirectly heated cathodes do use less power than filament type cathodes, dont they?

Correct, but that warm-up wait time for the indirectly heated cathode to reach safe operating temperature can be excruciating at times! 

Yeah thats why filament type cathodes are used a lot in  mobile gear because the filaments can be shut off when not transmitting and then come on instantly when it is time to transmit.

I thought ESSB required a compatible detector and software on RX to lock to the pilot?

There are plenty of fine sounding SSB signals, just find someone using a phasing system. These days Im pissed I sold off my CE 100V and 200V in the mid 80's for a pair of C Lines. :'(




And it fueled the explosive growth of CB >:(




Its 6 minutes on a YC-156 and 8 is better. But what a great linear tube. One of those would make me toss all the old iron and glass around here :D

Carl
KM1H

Last night I did something I have not done in a while, I tuned down to 3800 from the window  with the rx on LSB.  Every single SSB station I heard with no exception was way way over processed.  And there was a station about every 3 to 5 KHz.  And this was just ragchew operating, not cq contest or dx chasing.  Every last one sounded like they had run out and bought an RF speech processor and cranked it all the way up.  yeck.

Those are the ones I feel in no way apologetic about calling "slopbuckets".

I think that article is getting hams to try AM.  In one hour last night on 3885 I worked three guys all running Icom rigs driving amps.   They were giving AM a try.  One was an older ham returning to AM.  One guy down somewhere in Georgia I think, was running one of the Icom fish finder rigs.   He had a big signal and I assumed he was driving a big amp.   Turned out it was an AL80B.  That's an Ameritron amp with a single 3-500.  According to Ameritron, the no-load Ep is 2.7 KV.  Don't know how much Ip CCS, but with stock SSB cooling on the tube and the 400 ma max Ip on a single 3-500 you can do a little math and figure on running one at around 125 w.  while keeping an eye on things.  He said he was running 500 w.  I assumed that was pep but no, he said 500 w. carrier because Ameritron says it is a 1 KW amp.  I explained what I just wrote above but he never came back to me afterwards.  I hope he had a wildly inaccurate watt meter.    He was keeping his transmissions very brief, no more than a few seconds each time.  :(   

I'm surprised he didn't try to run 1KW of carrier.  ::)

He probably did but the Icom "fish finder" will only give so much drive.  Wow! How much drive do you need to have 500 watts of carrier on a single 3-500Z?!  The Henry 2K-4 runs a pair with 3200 volts on the plate (proper cooling and rated for continuous duty).  12 watts of carrier gives me about 200 watts back, 15 gives about 250, 20 gives 300.  The manual mentions loading it up for 350 watts of carrier but that would take more than my DX-60 can provide.  I cannot disable the ALC on my Kenwood ricebox and 25 watts of carrier results in the carrier heading south with modulation, not a very good am signal to amplify.

What the heck is an Icom "fish finder" rob? lol  I guess it's one of those FX-2000 or 9000's with the Display unit?  Maybe some of those are 200 watt pep and will do 50 watts carrier when maxed?  That could push that 3-500Z I suppose into cherry red plates... :)

It's amazing how much I have learned in 15 months of AM'ing and how much I still don't know!

fish finder is just a slightly derogatory term for panadapter.   There are now good panadapters with the SDR rigs but originally Icom came out with the little TFT displays that were not very accurate.  They fueled these spectrum conservation cops who would judge someone to be wide based on their tiny Icom display. 

The great scandal about the AL80B in my opinion is that with around 2400 v. under load from the p.s. to get near 1 KW out you'd have to beat the poor little single 3-500 to death with around 600 ma Ip at 65% effiency which is 50% more than it is rated for max.  All these idiots who buy that amp and believe the Ameritron hype have to get a new tube every 3 years or so. 

The Icom should not be run at more than 25 w. for symetric AM so he was probably running more than that carrier for drive.  He probably did not know it but his ALC may have kicked in and limited his pep drive, saving him somewhat.  I did not think about that before.  Like most modern amps the PA in these s.s. ham rigs may not be capable of buzzard AM transmissions, even running at 25 w.  YMMV in that some may be okay, maybe.   With a 100 w. rig that has an exposed PA heat sink I'd certainly put a fan on it and probably run it at no more than 20 w. if I'm going to make a 10 or 20 minute tranmission.     

You should be able to get 250 watts of 100% symmetrically modulated carrier with a 3-500, running it at maximum plate dissipation.  Assuming about 33% carrier efficiency and 2400 plate volts, the plate current should run a little over 300 mills for 750 watts DC input.  The question is, would the power supply deliver that much current during a lengthy transmission at 100% duty cycle.

Single 3-500 is rated at no more than 400 ma Ip; 130 ma Ig.   250 w. carrier okay but once you start modulating it very much you exceed the 400 ma Ip limit.   And as you indicate, there are all the other limiting factors--cooling, power supply continuous current limit and the tank circuit components may not all be up to continuous duty as this thing designed to be a ssb cw linear amp.   

From the AL-80B manual:

"The carrier power must be kept below 200 watts for clean and safe AM operation. With 200 watts of
carrier, the peak envelope power will reach 800 watts with 100% symmetrical modulation. The
modulated AM power output should be limited to 1000 watts peak with non-symmetrical
modulation that enhances the positive peaks."

You are quoting the AL80B manual as if it is an authoritative source on how to treat a single 3-500.  This was written by Ameritron.  These are the people in the business of selling an amp with one 3-500 that they call a 1 KW output amp.   It is nothing more than a b.s. sales campaign (1 KW sounds so much better than 700 w. -- a Kilowatt!!! woo woo)  and using this in a technical discussion is like saying cigarettes don't cause lung cancer because the tobacco industry chief executives all said so.

Sure you can drive the amp to whatever output but for how long?  30 seconds?   And when the 3-500 fails or something else goes which it surely will (but the amp will be out of warranty by then) don't expect a refund from RF Parts or whomever the vendor is because I guarantee you they'll send it back saying the tube was abused.  Now, if all this meets your operating criteria FB, otherwise, it's a ~125 w. AM amp, maybe a bit more if you do some mods.

Ameritron's operating limits are right in line with Eimac's recommendations for max output when used in AM linear service.

Have you owned or borrowed one these amps to test it out to see if it can handle it?  On what experience do you base your conclusion that it is incapable?

Why the Ameritron bashing?

At most, a single 3-500 is good for 1 kW PEP output. That would require running well over 3 kV on the plates. So 200 watts carrier at 2400 volt means 800 watts PEP at 100% modulation, probably on the hairy edge or over it. I run a pair at 2500 volts and much over 300 watts and the tubes run out of head room.

I've never seen an Eimac spec sheet that mentions anything about AM linear service. Referring to the spec sheet, we find the following for linear service.

Plate V         PEP Output (W)          Max AM Power (PEP/4 W)    
 1500               330                         82.5
 2000               500                         125
 2500               600                         150
 3000               750                         187.5

My point in quoting the manual was that Ameritron does, indeed, recommend keeping the carrier level below 200 watts (which that guy with the fish-finder obviously didn't read).

I wasn't recommending that it should be run at 200 watts carrier.

Steve,

I assume those Eimac figures are not taking into account losses in the output network so actual useful power at the antenna terminal will be slightly lower.

Wasn't amateur usage the prime market for the 3-400Z and later 3-500Z tubes?  If so then a pair was likely designed to comfortably run the old 1KW DC on CW / 2KW PEP SSB.

Drake rates the full carrier AM input for the L-4 (2 x 3-400Z) and L-4B (2 x 3-500Z) at 500 watts DC carrier in.  This is a reasonable rating for a fairly rugged amp with a decent power supply and forced air through chimney cooling.  With the matching T-4X series controlled carrier AM transmitters they can run at full input rating.  Controlled carrier rigs are much more friendly to modern linear amps and they can sound very good on the air.

Ameritron has some quite decent products and as a Mississippi native I am definitely not biased against a home state company.  Ameritron is similar to most companies, they tend to push the ratings in their advertising and in that regard they are no better or worse than most of the competition.  I remember being around some Henry amps (3K or 3K ultra) that used a pair of 3-500Z's rated at 3 KW PEP/2 KW DC and they were not reliable at that power level but they would have made an excellent legal limit amp in amateur service.

The Henry 2K-4 runs a pair of 3-500Z's with 3200 volts on the plate.  The manual states at 1KW input the pair will run 350 Watts carrier.  The amplifier is rated for continous duty.  The driving carrier power is around 25 watts to get the 350 watts carrier.  I run my DX-60 somewhere between 12 and 18 watts carrier to give 200 to 300 watts carrier.  If I had an exciter that would do a clean 25 watts AM it would give back 350 watts.  If I can get rid of that little bit of hum that's left I'll be all set!  I'm making progress with it.  At any rate, I feel a bit better about not worrying about the "cooling cycle" like I do with the SB-200.  I tend to make my transmissions short when using the SB-200 even at 100 watts.  

http://kx5jt.net/files/2K4%20Operating%20and%20Maintenance%20manual.pdf (http://kx5jt.net/files/2K4%20Operating%20and%20Maintenance%20manual.pdf)

As for the AL-80B, I know 500 watts of carrier seems highly unlikely unless your driving it way hard and something is bound to give at that level.

Yep.

2kW PEP input - makes for about 1200 PEP output. That would allow one to run about 300 Watts on AM, assuming the power supply can handle it and the tube(s) dissipation is (are) not exceeded.

A pair of 3-500s with 3800-4000 Volts on them will produce 2 kW PEP output. Most of the pre-power level change amps like the L4 ran less than 3000 Volts on the plates.

If he was running it at 500W out, he won't do it for long, heheheh. I've been running one on my 10 meter repeater since 1994. When I first installed it, I ran the full plate voltage as shipped and drop it to about 500W. Only lasted a few days before a trip to the repeater site yielded a 80B witha toasted transformer. Checking the tube in another amp, it was already soft as well.

I bought a replacement transformer and connected the HV taps to the lower voltage windings.  I don't remember the exact voltage, but there was a lower voltage unused tap generated about 1800 vdc or so from the supply. I installed a new 3-500C. I also installed an additional fan pulling air out of the cabinet near the tube compartment. It has been running at 300w output ever since, with no problems.

It's about time to replace the tube, as it's only running about 150w output now, but 15 years or so in repeater duty is pretty good, methinks.

Dave WB4IUY

I wonder if there is a way to run the amp in class C for 10 m. FM. 

Hi Tony, I'm not trying to bash Ameritron and if I was harsh I apologize.   There are a few things they do that irritate me but some of their amps are okay for the money if all you want to do is operate ssb and cw.  If I wanted an amp for those modes I would probably buy an AL82 because it cheaper to buy one than build especially if I got one used.  (But I'd probably reduce the plate voltage from the stock 3.3 KV under load).   I am no engineer and in fact my limited knowledge extends only to 3-500 amps because that's what I run and what I have studied to determine the safe parameters for AM.  I have never owned an AL80 but I know some of the specs and what a single 3-500 is rated at:  no more than 400 ma Ip and 4 KV Ep and 130 ma Ig, grid diss. 20 w. plate 500 w.  There is a little fudging on the Ip -- you can supposedly exceed 400 ma provided you do not for more than 5 seconds, but by how much is unclear.  I know Ameritron says the 80B plate supply is 2.7 KV no load.  Let's pretend it doesn't sag at all under load and the amp is 70% efficient.  So, I'm being liberal in my operating envelope.  2700 x .4 x .7 = 756 watts.   To get to 1 KW under those (unrealistic) circumstances the plate current would have to be 530 ma!   But they sell a "1 KW" amp and any operator who foolishly believes this is likely buying a 3-500 every few years, when such a tube should last decades if treated right.  Now, you quote a portion of their manual in which they counsel keeping carrier under 200 w.  But this is also disingenuous for they immediately speak of limiting the peak power to 800 w. which as we have seen is already excessive, and 1 KW for assym. modulation.   Of course having sold a "1 KW" amp, they can hardly back away from that in the manual, hence the conflicted information you quoted.  I would be interested to know if Ameritron supplies any specification on transmission time length for the 80 and other amps they sell.  Some mfrs for example derate the power for continuous duty and give a time length. 

Generally, there are several factors affecting a commercial linear RF amplifier for AM service:

The plate power supply--voltage doubler or full wave bridge, and the transformer's CCS rating
Tube plate dissipation
Cooling -- most amps made for SSB/CW are sold as quiet amps, meaning the cooling is not adequate for AM
Tank circuit in particular the inductor and bandswitch
H.v. choke and parasitic suppressors -- can the choke withstand continuous carrier and is the par. supp. construction made to withstand the added heat from the anodes
Length of transmission time -- who wants to operate with one eye on the plates and a timer?   This is why a lot of hams who run amps on AM homebrew their own.
 
Since SSB got really popular and FCC started cracking down on the manufacture of relatively high power amps sold to Americans (Henry 8K, two hole Alpha) and costs have gone up, amp manufacturers have gotten pretty good at engineering amps without a great deal of margin for operation beyond the power and duty cycle they are sold for.   The change is most shocking when you take a look at an amp made for AM as well as other modes such as the older Hallicrafters amps and the Chippewa. 

To be sure, most if not all ham amp mfrs fudge in various ways in their advertised specs but I think Ameritron is egregiously misleading with this one product.  I also think it is irresponsible of them to sell their cheap solid state amps that can be overdriven to put out a lot of garbage up and down the band.  Maybe they have cleaned them up but it used to be that ALS600 was bad news.   Anyway, my opinions and worth what you paid for them  :D

73

Rob

Brian said:

 ;D ;D ;D  ;D ;D ;D

Rob,

Thanks for the apology.  I hope I wasn't being oversensitive.

I pretty much agree with everything you said.  I think Ameritron has gotten better over the years about rating their amplifiers realistically, but they still have a ways to go.

There will always be those in our hobby who will abuse these devices no matter what the manufacturer says, and then complain loudly when it melts down.  It's a tough predicament for any company to deal with, but it's not helpful when they are unclear about their our ratings.

Tony

I am reminded of the days when home stereo retailers and manufacturers offered wildly exaggerated claims of audio output power, based on a measurement method established by the IHF (Institute of High Fidelity).

It was something less than "peak" wattage, but a lot more than say a continuous power rating or a more average reference.

Often this IHF measurement, called "music power," was into 4 ohms rather than the more ordinary 8 ohms of typical household loudspeakers. Further, some marketing strategies quoted a power that was calculated from combined channels, without so stating.

Another deceptive tactic was to use an EIA-based measurement standard for audio power which was assessed at a far higher level of distortion.

Eventually buyers and consumer advocates wised up and the marketplace shifted to what I think is an RMS-based system of power ratings.

Then there's BOSE, who today in their car stereos REFUSES to disclose any power measurement at all. The company instead offers pabulum "we think it's more important that the buyer hear the sound of a well-designed system, than to obsess about power ratings."

That's the jist of what I read in the Mazda owner's manual anyway.  And yes, the stereo is underpowered.

Ah-hehnh !