QST AM Article and SSB Power

[K5UJ]

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.     

[N3DRB The Derb]

he said 500 w. carrier because Ameritron says it is a 1 KW amp.

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

[KX5JT]

he said 500 w. carrier because Ameritron says it is a 1 KW amp.

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!

[K5UJ]

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.     

[k4kyv]

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.

[K5UJ]

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.   

[K4QE]

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."

[K5UJ]

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.

[K4QE]

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?

[Steve - WB3HUZ]

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

[K4QE]

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.

[WQ9E]

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.

[KX5JT]

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

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.

[Steve - WB3HUZ]

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.

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.

[wb4iuy]

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. 

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

[K5UJ]

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 

73

Rob

[W3SLK]

Brian said:

P.S. Did MFJ ever acquire the ARRL too? http://fi-ni-report.blogspot.com/2009/08/mfj-to-acquire-arrl.html

   

[K4QE]

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

[WA3VJB]

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 !