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Author Topic: 3-500ZG Tube Brands  (Read 4596 times)
NI0C
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« Reply #15 on: September 17, 2003, 04:33:13 PM »

To N0SP:

Where's the CW switch on the AL80B?  Mine doesn't have a mode switch!
 
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WB2WIK
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« Reply #16 on: September 18, 2003, 01:26:35 PM »

I'd add a few points of clarification:

-The AL80B doesn't have a "CW" position -- it runs at full plate voltage (3000-3500Vdc) all the time.

-It's irrelevant to use Eimac data regarding 3-500Zs nowadays, since Eimac hasn't manufactured a 3-500Z in years and the new AL-80Bs ship with Amperex (French) 3-500ZGs.  The Eimac data sheet indicating 400mA max Ip doesn't agree with the Amperex data sheet, which indicates 500mA max Ip.  

-One needn't use an outboard peak-reading wattmeter with the AL-80B, since it has a peak-reading (electronic peak sample & hold detector, powered) wattmeter internally, with a front-panel meter.  While of questionable accuracy (mine is within about 10% on most bands, under most conditions, compared with my outboard Bird 43P), it is a true peak reading circuit and is fine for pulse tuning.

-I wouldn't recommend using the "FM" mode for tuning an amplifier (into an antenna) unless care is taken to turn the mike gain down to zero (or unplugging the mike altogether) first, since background noise will modulate the signal.  Using the CW mode with the key closed, or the RTTY mode, or the CW mode with the pulser, is a better idea.

WB2WIK/6
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NI0C
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« Reply #17 on: September 18, 2003, 05:33:54 PM »

I feel I should respond to an earlier post on this thread that implied that Ameritron likes to sell replacement tubes.  Based on my experience with them, I'd say that was very unfair.  In my review of the AL-80B under eHam Product Reviews, I reported that Ameritron replaced my 3-500ZG for FREE when my original tube went "soft" after a couple of years of use.  They didn't have to do this-- they had ny credit card number and I was willing to pay for the replacement.  They asked me to return the old tube to them for evaluation, which I did.  They never charged me for the new tube.  Good guys, those Ameritron folks!
   
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W1DY
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« Reply #18 on: September 18, 2003, 10:19:25 PM »

I hope I didn't start a WAR here!

Right now I have An Eimac 3-500Z in there..and have a RFP 3-500 ZG on it's way....
(read higherup and see what happened to the original they sent)

Anyway...With what I have ...
I tried tuning up the amp...and what I'm seeing is that on voice peaks...with @350 lp...
I can still hit @1000-1100 watts on the output meter!

The SWR is barely moving so almost nothing back!

Normal voice @750-850 Out.

Place and Grid are WAY below MAX...

On tune up...(pulsed CW)I get @400 lp at @70-75 Watts Drive.

By all readings the ALC level seems fine.

Anyway...All I can go by are the meters I have....
I will take the advice here to heart..and watch those meter readings so as to not spatter.


I'm impressed with this amp...!

So many years running my FT-990 Barefoot!

Thanks for all the great info!
Now to get my Husband to learn CW to get his ticket...

HOLD THAT THOUGHT...If he get's his ticket..I'll never get my Mic Back!

73
Wendy

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N0SP
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« Reply #19 on: September 18, 2003, 11:42:50 PM »

Hello Wendy...
   Don't worry, you didn't start a "war"...  I'm glad that you clarified that you were using an EIMAC 3-500Z since thats the tube I was referring to in my comments.

   The reason I suggested using FM mode for tune up is because thats the ONLY way you'll see an accurate indication of the actual input power to the plate.  If you're using the pulser and the meter on the amp reads 400ma Ip current the actual value is somewhat higher because the meter is reading the AVERAGE value rather than the peak value.  To preserve cleanliness of output you don't want the peak value exceeding 400ma.  When transmitting with SSB the peak value is far higher than what the meter is saying. The same is true of the grid current readings.
  I'm not suggesting that you continue forever to use FM for tuning up, but do it until you get a good handle on where to set the exciter power level.  Then once you learn it you can return to that value on the 990 and tune up any method you like and be assured you're not overdriving the amplifier.  Like I said, the amplifier will deliver around 750 to 800 watts out.  Be aware, however, that while talking the typical wattmeter will only show about 200 watts out.  A true PEAK reading wattmeter will show much higher, close to 750 watts IF it's got a good hold circuit on it.  The meter on the amp IS a peak reading wattmeter, but it has no hold circuit, so with normal talking it will bounce up around 500 or so.
 An excellent accessory in the shack is the Palstar WM150 wattmeter.  It's a true peak reader, is very accurate (tracks perfectly with 2 Bird wattmeters I have) and is priced well for hams at $109.95.  Four of my friends have them and all are really happy with them.  I would get the WM150M, which is the mobile version.  It's circuitry, cabinet, and performance identical to the base version but it allows you to place the line sensor anywhere in the shack thats convenient to hook to the coax. Then you can put the meter in plain view without having to route coax up to and behind the box.  The nice part about it is that you will be able to read your actual peak output as you talk.  It has a dual-movement meter showing reflected power and SWR so it works great for tuning the antenna.
www.palstar.com
  Now, having said all that, someone posted above that the AL-80(X) has a "peak and hold" circuit.  Maybe later versions do, mine does not.  So, if it indeed DOES have a good hold circuit then it might do just fine.  I have two Ameritrons here and both meters are horribly innaccurate at the low end of the power scale.   They are very close, however, near the range of the amps ratings.  Strange, but thats how it works.  My AL-1200 is very close at the 1200/1300 watt level, but at 3 or 400 watts it reads about 40% high!  The meter on my AL-80 is the same way reading about 30% high at 200 watts.  And remember, the "peak reading" feature in the amp ONLY refers to the power output, NOT the plate (Ip) current!  The ONLY time the Ip current meter is accurate is when you're keying the amp with a steady carrier.

  Good luck and enjoy the new toys!
Dennis
NØSP



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W8JI
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« Reply #20 on: September 25, 2003, 07:09:40 AM »

Dennis is trying to be helpful and I'm sure his intentions are good, but his detailed replys really contain some serious misinformation.

There is nothing wrong with Ameritrons tuning or operating instructions. You should ALWAYS tune the amplifier for maximum output with FULL drive from the radio, NOT with 60 watts as he suggests. Tuning with 60 watts will virtually guarantee excessive tank voltages (arcs, which by the way do NOT very often if ever come from parasitics)and flat topping (splatter).

What he forgets is that rigs commonly have ALC overshoot, and most have no real drive control. They depend on notoriously slow ALC to limit power. If you tune at 60w and the rig hits 100w or more for a millisecond while ALC kicks in, you can damage a bandswitch or tuning cap. Once an arc triggers it ionizes the arc path and even when power cuts back the arc will continue!!!    

At the rated IVS specs from Ameritron, the 3-500Z is substantially cleaner than most radios on the market. The IM limit is in the radio, not in the amp, if you load properly. People get dB below PEP and Db belone one tone confused. A typical radio is -33dB PEP, which is -27dB one tone. The 3-500Z run at 600mA peak in IVS service is -32dB to -35dB one tone (third order), which is better than most radios. The real splatter that annoys people is higher order IM caused by non-linearity in semiconductors in the radio, and extends out for several kHz. It isn't the close in stuff caused by a slight slope in waveform at the tube.

Of course if you underload the amp, all sorts of bad things happen. That's why you ALWAYS want to tune for maximum available drive, and NOT use a radio that runs 150-200w out with the AL80. You don't want to use a rig with significantly MORE than 100w to drive the AL80.

Most of the above is explained at and documented at:

http://www.w8ji.com/Amplifiers.htm

Also, the Ameritron factory specs were approved by Eimac, as IVS operating specs. IM distortion was tested, and the tube is absolutely fine running at Ameritron specs. The tube does not, as some seem to believe, operate fine for years at 750W and go to heck at 20% or so more power.

As for filament voltage, it makes a big difference when the tube is on 24 hrs 7 days but you'll never notice the life change in Amateur service unless you do something drastic like run 15% or more excessive voltage. Most 3-500Z failures are arcing related due to material or manufacturing defects such as outgassing of elements, seal leakage, or failure of manufactures to pump down the tube enough. Filament emission life failures, which are the only failure related to filament voltage, are VERY very rare.

The 3-500Z getters (removes gas) by a catalytic action in the Zirchronium coating on the anode. That's the gray looking coating. In order to activate, the tube has to be red hot on the anode. If you have a tube sit for months with being operated it can leak via seals or release trapped gas in the materials inside the tube and arc when you power it up! So it is NOT good to store 3-500Z's for a long time without using them.

People will worry you to death about the 3-500Z and other things, mostly because people love to talk about amplifiers, but the truth is most tube failures are because high power tubes are VERY difficult to manufacture corectly. Historically tubes are becoming less and less reliable as older people retire and manufacturers cut costs. Tubes have ALWAYS been the shortest life component in electronic equipment. That's not some secret, it's been known for many many years. Even low power low voltage easily operated tubes failed so often virtually every drug store in North America had a tube tester and sold tubes!!

All this chatter about doing this and doing that to save filament life and all the worries, and virtually ALL 3-500 failures are almost always due to problems entirely unrelated to HOW you operate the tube!!!!

The biggest sin you can commit with the tube is running the tube anode white hot to the point where it melts, or running it stone cold!! Neither is good.

The biggest problem for components like band switches and tank capacitors is tuning the amplifier with LOW drive at the last tuning step, like 60 watts drive!!!

You can see why on my website. It is ALL documented.

73 Tom
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N3ZKP
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« Reply #21 on: September 26, 2003, 02:24:19 PM »

This has been the single most informative thread I've read on eHam. I have learned quite a lot about the 3-500Z and about correctly operating my AL-80A.

Thank you to Wendy for starting the thread in the first place and to all who posted, even if the opinions varied Smiley

Lon
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N0SP
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« Reply #22 on: October 02, 2003, 05:29:42 PM »

Hello Wendy, et al,

Well this thread has turned in to a good discussion of amplifier tuning techniques.  I think it's good even though it's gone beyond your original question of how to tune the amplifier.  It's all in fun.

My frequent travels due to my work preclude quick replys sometimes.  W8JI, who made a previous posting, is an active participant in the hobby and should be complimented for sharing a lot of good stuff with the world.  I have incorporated one of his mods to my FT-1000D with a happy result.

However, I'm convinced he did not read all of my comments with regards to tuning the amplifier, to wit;

TOM WROTE:
"Tuning with 60 watts will virtually guarantee excessive tank voltages (arcs, which by the way do NOT very often if ever come from parasitics)and flat topping."

Taken by itself, Tom's comment is correct. However, it is ONLY correct if subsequent operation after tuneup allows the full 100 watts from the exciter to the amp. Tuning up with 60-70 watts then driving the amp with 100 watts virtually guarantees splatter, excessive grid current, angry neighbors, and all kinds of bad things.  I stated repeatedly that the power to the amp MUST be limited to the value to which it was tuned.

TOM WROTE:
"What he forgets is that rigs commonly have ALC overshoot, and most have no real drive control. They depend on notoriously slow ALC to limit power."

Again, Tom must of missed my comments. On at least two occasions in my previous posts I clearly stated that you should NOT rely on ALC for the EXACT same reason Tom gave.  We seriously agree here.  It gets a little complicated to apply this easily to all radios since, like he said, some radios lack an accurate power output control.  But Wendy, your FT-990 has a good one that very effectively limits the power output to the value you select without overshoot.  

TOM WROTE:
"At the rated IVS specs from Ameritron, the 3-500Z is substantially cleaner than most radios on the market. The IM limit is in the radio, not in the amp, if you load properly."

It is true that the 3-500Z is cleaner than most radios WHEN RUN WITHIN the specifications published by the manufacturer of the tube.(EIMAC)  Whatever garbage goes into the tube also comes out... stronger.  Eimac rates this tube with a very good 3rd order IMD of -40db running 740 watts output at the max plate current of 400 mils. (around 65 watts drive, 3,000 volts on the plate)  This is better than most transmitters running full output, HOWEVER, when you lower the output from 100 watts to 60-80 watts the transmitter becomes cleaner.
Tom states that they measured the 3-500Z at -32db with 600 mils.  Minus 32 db is not a bad number, but frankly, I'm reluctant to recomend that since it's pushing the tube more than FORTY PERCENT higher than it's maximum rating allowed by EIMAC, the people that build the tube.  If we are to believe Tom's claims of -32db (and I have no reason not to, but my instinct tells me it's a bit optimistic) his posting makes my point.  Eimac rates the tube at -40db with 400 mils on the plate, (cleaner than Wendy's FT-990) Ameritron measured it at -32db, with 600 mils, an 8db deterioration that is now dirtier than Wendy's FT-990.  So the amplifier now becomes the bigger player with IMD distortion emissions now about SEVEN times higher than they are at the 400 mil level.  These numbers are not my invention.  The -32 number is provided by Tom, the -40db number comes straight off the Eimac data sheet.  

  These days there are several very clean transmitters available. Wendy, your FT-990 is a very good -38db when running at 100 watts. Its even better at 70 watts.

Some of these are "fine points" that won't quickly kill a tube when operated either way.  The SSB duty cycle on an AL-80 is such that it won't burn the tube out of the socket if you hit it with 100 watts of drive. My comments were coming from wanting to enjoy the purity of emission that Eimac advertises for the tube.  As I tune around the band these days and look at the scope attached to the I.F. ouput from the receiver I see far too many "dirty" signals.  I'm sure there are a lot of reasons for them, I seldom stop to ask what people are running when I see wide signals. So my idea is to help prevent as much trash on the band as possible.

It boils down to this.. Eimac BUILT the tube, not Ameritron... From the horse's mouth, the link below (courtesy of WB4HFN) is the Eimac data sheet on the 3-500Z.  It shows the maximum ratings and "typical operation" specs for several types of service... Plate modulated class-C transmitter, oscillator/amplifier, linear.. grid-driven and cathode driven.  NO PLACE on the sheet is there any permission or rating that suggests operation higher than 400 mils.  In fact most of the "typical operating" charts indicate values between 275 and 350 mils. The only chart that allows 400 mils "typical" is the SSB linear service.  It also shows it as the "maximum" value.  See it for yourself at
http://www.wb4hfn.com/DrakeArticles/Xmit_Tube_02.htm


For me the "grey area" here just how much more can you push it before you get a REAL perceivable deterioration in output purity.  I can't answer that.  Perhaps we all have different standards.  Tom's idea of running 100 watts in to the amplifier may not be as bad as my perception of what would happen.  Perhaps I'm over cautious, the fact that I haven't had to change a SINGLE output tube in ANY transmitter or amplifier I've ever owned in 33 years of operating may suggest I'm a bit conservative.  But I've never had one fail due to gas (under-use) either.  It's my nature to operate that way... in my work I fly a $45 million airplane and you can bet your cookies that I'm not operating any part of that thing at 40% greater than what the manufacurer recomends!  Nor would you want to ride in it if I did.

The rundown here is:

1971 FT-101B, daily hard use until 1979.  Still has tubes it came with, little use today. Runs full output.

1978 FT-901DM, heavy daily use from 1979 to 1990, and mostly on AM(!).  Loaned to a friend for 2 years after that, original tubes, occasional use today, still full output.

1989 to present.. FT-102, I put a fresh set in when I bought the radio, used heavily for 14 years.  Tubes are still perfect.

A nineteen FIFTY-SEVEN Johnson Viking 500 AM transmitter.  Still has the original Amperex 4-250 final output tube. (FORTY SIX years!) Periods of heavy use, now occasional.

AMPLIFIERS:
Heathkit SB-1000, (clone of the AL-80) 1989 to present, original 3-500Z, perfect condition, few thousand hours on it.

Ameritron AL-1200, 1986 to present... few thousand hours on it, original tube that came with the amp, full output today.

Tom's right about manufacturing techinques going downhill.  I've not been witness to it personally, since I haven't bought any output tubes in 20 years, but I do know of others who got tubes with poor internal alignment.  It's an imperfect science.

So Wendy, and others, chose your method.  If you want to get the very last "watt" from the thing you can probably run it with 100 watts of drive and the tube will last a long time, likely until you're tired of the amplifier.  Tom's comments about tube life are probably correct, he certainly has more experience with amplifiers than I do.  But if you want full confidence that your signal is as clean as Eimac designed it to be and you don't mind running 750/800 watts instead of 1,000 and would prefer additional "margin" for accidental mis-tuning, etc.,  then you now know how to do it..
Good luck everyone!
73,
Dennis
NØSP
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W8JI
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« Reply #23 on: October 03, 2003, 01:50:57 PM »

Hi Dennis,

>>>Taken by itself, Tom's comment is correct. However, it is ONLY correct if subsequent operation after tuneup allows the full 100 watts from the exciter to the amp. Tuning up with 60-70 watts then driving the amp with 100 watts virtually guarantees splatter, excessive grid current, angry neighbors, and all kinds of bad things. I stated repeatedly that the power to the amp MUST be limited to the value to which it was tuned.>>

The problem with that statement is you are asking for an impossible operating condition, and presenting grossly exaggerated results for what really amounts to a non-problem.

ALC systems in radios are commonly notoriously slow on attack, and virtually ALL have overshhot on leading edges. Very few people have fast responding storage or long-hold meters to watch peaks, and very few people would understand what to look for.

Tuning instructions MUST be tailored for the likely operating condition and NOT something that is almost certain to cause problems.

When you start paying for warranty parts and become responsible for a manufacturer's reputation, you can re-write the operating manual! Until then, please let the factory do it.      

>output control. But Wendy, your FT-990 has a good one that very effectively limits the power output to the value you select without overshoot.>>>

...and we know that because???


TOM WROTE:
"At the rated IVS specs from Ameritron, the 3-500Z is substantially cleaner than most radios on the market. The IM limit is in the radio, not in the amp, if you load properly."

>>It is true that the 3-500Z is cleaner than most radios WHEN RUN WITHIN the specifications published by the manufacturer of the tube.(EIMAC) Whatever garbage goes into the tube also comes out... stronger.>>>>

First, Eimac specs that tube at continuous service, not IVS. I am using an IVS rating approved by Eimac was back in the early 80's. Let's not put that important point aside. Some manufacturers are not as dumb or careless as some people would have others believe. Eimac fully warranteed the tubes sold by Ameritron, and even reviewed the manual. There was never a single case of failure due to following the manual. Life is a non-issue. Eimac had no issues with it, lab tests showed no problems, and field failures or complaints did not reflect any problems.  

Second, you are mixing dB below PEP with dB below one tone. Eimac and I use the commercial standard method of dB below one tone. Radio manufacturers and the ARRL use the "non-standard" dB below PEP.

To adjust the two, you have to deduct 6dB from specs of radios and from ARRL measurements.

>>These days there are several very clean transmitters available. Wendy, your FT-990 is a very good -38db when running at 100 watts. Its even better at 70 watts.>>

Many radios actually get worse at lower power, but the -38dB you quote above is below PEP and for two steady tones. That translates to -32dB PEP, which is NOT particularly clean when you consider an old KWM-2 from 1960 is typically in the -40 to -50dB range.

The AL80 series maintains IM performance even with voice signals, the FT-990 will not. The reason is radios have notoriously poor biasing and power supply systems, and they waddle around with various frequencies loading the supplies. They just aren't as good as you think, and certainly are the major limit in system IM. The exception is some commercial tetrode amps with poor regulation and low negative feedback, they qactually are worse than radios!  

>>Some of these are "fine points" that won't quickly kill a tube when operated either way. The SSB duty cycle on an AL-80 is such that it won't burn the tube out of the socket if you hit it with 100 watts of drive. My comments were coming from wanting to enjoy the purity of emission that Eimac advertises for the tube.>>>

Then you'd better go purchase a KWM2. ;-)

Otherwise, you are radio limited.

>> As I tune around the band these days and look at the scope attached to the I.F. ouput from the receiver I see far too many "dirty" signals.>>

I'm not aware of any bandscope than can accurately measure signal BW. The measurement device would have to have significanly less BW than the signal it was measuring. Bandscopes do not.

Amplitude measurements from a receiver are worse yet. With AGC, they display the effects of AGC and ALC systems. Looking at audio peaks on a scope actually gives no indication at all if the signal is wide or not!!! The only accurate way to estimate linearity is to sample the RF in front of and after the amplifiying device.

The only accurate way to measure BW is to measure bandwidth. The only accurate way to tell the cause is to be at the station when it is measured, not 1000 miles away!!!

The 3-500Z saturates at over 2500 watts of RF output on peaks. It is VERY unlikely you are seeing tube emission saturation, if you are actually seeing anything at all that is meaningful.

Upper emission current in a thoriated tungsten filament is roughly approximated by filament current times voltage (power) times .1. In larger tubes it approaches .15 times power. If you can actually "see" flat topping on the scope from an amplifer, it is probably becuase the tube has VERY low emission or they have the loading control too far shut (probably from tuning at low power).        

>> It boils down to this.. Eimac BUILT the tube, not Ameritron... From the horse's mouth, the link below (courtesy of WB4HFN) is the Eimac data sheet on the 3-500Z. It shows the maximum ratings and "typical operation" specs for several types of service... Plate modulated class-C transmitter, oscillator/amplifier, linear.. grid-driven and cathode driven. NO PLACE on the sheet is there any permission or rating that suggests operation higher than 400 mils.>>

I really don't think either you or some "unknown" WB4 can trump Eimac's own engineers, as well as characteristic curves published by Eimac. Data sheets list "typical" measured specs for one form of operation based on 24hr a day 7 day a week operation.

IVS service is a well known form of operating.

Perhaps we should look at transformers, and see how thay are abused in amateur service?? A typical 35 pound hypersil has a "core rating" of about 1200VA. Why not use a 35-pound transformer in a single 3-500Z amplifier? Because of the service!!! This isn't CCS.

It never fails to amaze me how operating two or three of something a few hours a week makes people more experienced than people who have spent 30 years of 40-50 hour weeks looking at problems and talking with the design engineers of components!!

Had you quoted WA4GPM, who was a designer of high power tubes and engineering R&D manager at Eimac-Varian's power grid tube plant where 3-500Z's were made, I would have been impressed. But some unknown WA4 with a webpage showing a tube data sheet really doesn't trump the product engineer who looked at that design and said it was fine.

73 Tom
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N3ZKP
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Posts: 2008




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« Reply #24 on: October 03, 2003, 03:09:12 PM »

Tom:

Just to get things straight in my aging mind ...

You are saying to tune up my AL-80A with the full 100w drive from my TS-570 and THEN drop the drive back to give me either:

(1) the desired output
(2) whatever a max Ip/Ig of 400ma/150ma will give me.

Am I correct? That's the way I have been tuning the amp to date. We are talking SSB here, not key-down modes or CW.

Can I or can I not run with 100w drive for a full KW+ (PEP) output?

Thanks,

Lon
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N0SP
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« Reply #25 on: October 03, 2003, 09:02:58 PM »

Good Evening Lon..
   You asked what you can do... well, you CAN do anything... I guess.  Loading up the amp with 100 watts drive then reducing power to some lower level is a very SAFE way to run the amplifier, however, it's not the most efficient.  If you apply, say 70 of drive, then tune it up you will get a certain output.  But if you tune it up with 100 watts of drive, then reduce your drive to 70 watts you will have LESS output than if you just tune it to 70 watts.  It has to do with how "linear" amplifiers work with respect to impedence matching.  It's a bit of a story so I won't go in to it here.  Like I said before, just make sure that if you tune it to 70 watts of drive that your radio doesn't overshoot to more power.  Some radios do a great job of that, others do not.  In one of my radios I had to build a box with a 9 volt battery and a precision pot to apply a steady voltage in to the ALC input on the radio.  I call it my Dial-a-Watt.  It absolutely limits the radio at the prescribed power down to a few hundred milliwatts with NO overshoot.  

With respect to what Tom said... and I'll say here that I'm not going to continue this kind of exchange which serves to confuse readers over what amounts to different operating styles.

Tom wrote:
"ALC systems in radios are commonly notoriously slow on attack, and virtually ALL have overshot on leading edges."

Tom, how many times do I HAVE to say it???  I DO NOT and never have relied on amplifier-generated ALC for ANYTHING when it comes to using an amplifier.  You keep admonishing me on this point and I have said 5 times now that I don't recomend it for the very reason you cite!

>But Wendy, your FT-990 has a good one that very >effectively limits the power output to the value you >select without overshoot.>>>

>...and we know that because???

I am familiar with the FT-990's power control (NOT just the ALC!!!) I have a neighbor with an FT-990.  He limits it's output to 19 watts to drive a very sophisticated home brew amplifier using 3 tetrodes.  The 19 watts of drive produces 1,500 watts output.  If that radio's power regulation was "all over the map" believe me, we'd all know it here, and so would he.  This gentleman is a very accomplished engineer having spent his whole life in the field, holds 2 PHDs, and has built numerous amplifiers mostly using external anode tetrodes.  I'm less than two miles from him and his signal is very clean.

Tom wrote:
>To adjust the two, you have to deduct 6dB from specs >of radios and from ARRL measurements.
You're correct here, and I hadn't done that.  But it doesn't change the fact that the IMD numbers on the amplifier deteriorate as you continue to drive it harder.

>>Many radios actually get worse at lower power, but the -38dB you quote above is below PEP and for two steady tones.
Yes, some do get worse at lower power, but most get better.  Working the averages here.. especially since the amplifier's numbers get BETTER as drive power is reduced.

>My comments were coming from wanting to enjoy the purity of emission that Eimac advertises for the tube.>>>
>Then you'd better go purchase a KWM2. ;-)
Actually Tom, I come pretty close to that.. my FT-102 is rated at better than -40db.  With power reduced to 65 watts the 3 6146s are almost in to a Class-A condition.


>>I'm not aware of any bandscope than can accurately measure signal BW. The only accurate way to measure BW is to measure bandwidth.

It's not just a "bandscope"..
It's a Tectronics 564 storage oscilliscope, with a 3B3 timebase and a 3L5 Spectrum Analyzer (with a mixer) connected to the output of the two receivers.  When I hear buckshot on a signal I can tune it in, set the scope to "store" and in a few seconds have a pretty good picture whats going on.  The only limitation is that the signal has to be fairly strong.

Tom Wrote:
>>I really don't think either you or some "unknown" WB4 can trump Eimac's own engineers.

Tom, Did you look at the link I sent??  It isn't just some "unknown WB4" saying something... the link takes you to the ACTUAL EIMAC DATA SHEET published BY Eimac. You can't get any more authentic than that.  I have the same thing here on paper, FROM EIMAC.  I realize that these are CCS ratings.  And, I might add, CCS ratings for a properly cooled tube. (pressurized chassis & chimney)

You did mention transformers and power supplies.. That brings me to another reason that I don't like pulling 550/600 mils out of the AL-80.  At that high current the regulation starts to get pretty bad, especially with 120 volts on the primary.  I'm not concerned about the transformer since the duty cycle is low.  The Dahl transformers are plenty adaquate in that regard.

73, Dennis




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« Reply #26 on: October 04, 2003, 05:41:12 PM »

Tom:

Just to get things straight in my aging mind ...

<<<<You are saying to tune up my AL-80A with the full 100w drive from my TS-570 and THEN drop the drive back to give me either:

(1) the desired output
(2) whatever a max Ip/Ig of 400ma/150ma will give me.>>>

Yes. Absolutely. 100 watts or even more of drive, despite what some will try to tell you, will not cause a problem at all as long as the amplifier loading is heavy enough.

There is a technical reason for this, and it has to do with the very high negative feedback inherent in a GG amplfier. Most of the power is "fed through" to the output, there isn't excessive grid dissipation if you follow the manual.  

<<Am I correct? That's the way I have been tuning the amp to date. We are talking SSB here, not key-down modes or CW.>>

Even on CW, you should tune for full drive (assuming you don't have a huge rig, like a 150 watter).

Then back the drive down to rated (400mA) cathode current. This reduces voltage in the tank, increases negative feedback, and allows the amp to be much more more linear than tuning at 60 watts!!
 
<<Can I or can I not run with 100w drive for a full KW+ (PEP) output?>>

That amp is perfectly fine in IVS service if you load it correctly with 100w PEP drive. This all hinges on the fact you MUST load it heavily enough. The manual even says to go just slightly beyond the point of maximum output.

The key is watching grid current. Grid current reliably indicates proper loading. More than 150mA at full drive on carrier indicates excessive drive or insufficnent loading.  

The worse possible thing you could do is load it at low drive, and depend on ALC circuits to clamp the power. Virtually all radios overshoot, and even a few milliseconds of a transient can cause a damaging arc.

It's definately the lesser of two evils to tune at higher power and back off from that slightly.

73 Tom
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« Reply #27 on: October 04, 2003, 06:14:10 PM »

Hi Dennis

<<<that, others do not. In one of my radios I had to build a box with a 9 volt battery and a precision pot to apply a steady voltage in to the ALC input on the radio. I call it my Dial-a-Watt. It absolutely limits the radio at the prescribed power down to a few hundred milliwatts with NO overshoot.

I doubt it. The only thing external negative ALC does is limit gain. It does not add clamping. It actually decreases dynamic regulation, although the reduced gain might reduce overshoot.

Think about what an ALC system is.
 

>Tom wrote:
"ALC systems in radios are commonly notoriously slow on attack, and virtually ALL have overshot on leading edges."

Tom, how many times do I HAVE to say it??? I DO NOT and never have relied on amplifier-generated ALC for ANYTHING when it comes to using an amplifier. You keep admonishing me on this point and I have said 5 times now that I don't recomend it for the very reason you>>

Dennis, the reason I keep repeating it is YOU don't seem to understand it is the internal ALC that limits power in a radio. It has NOTHING to do with EXTERNAL ALC.

The ALC system INSIDE radios virtually always contains some overshoot. It has nothing to do with anything EXTERNAL.

When you turn down a pewer control, you change bias on a comparitor for internal ALC threshold. Turning the power down INCREASES the percentage of overshoot.
 
It is a BAD idea to do that in most radios.

Tom wrote:
>To adjust the two, you have to deduct 6dB from specs >of radios and from ARRL measurements.

<<You're correct here, and I hadn't done that. But it doesn't change the fact that the IMD numbers on the amplifier deteriorate as you continue to drive it harder.>>

Yes, but my point is the radios we have are the limiting device unless you have something seriously wrong in a PA, or are using a tetrode amp with poor regulation and no negative feedback.

Inflating the IM performance makes your arguement sound valid when it isn't.

>>Many radios actually get worse at lower power, but the -38dB you quote above is below PEP and for two steady tones.

<<Yes, some do get worse at lower power, but most get better. Working the averages here.. especially since the amplifier's numbers get BETTER as drive power is reduced.>>

No, that isn't correct either. IM goes through peaks and valleys as drive is changed. IM is more related to negative feedback than power in a GG amp, because negative feedback is so high. Tuning the way I suggest actually increase negative feedback. Tuning the way YOU suggest decreases it, because it raises the anode impedance.  

>My comments were coming from wanting to enjoy the purity of emission that Eimac advertises for the tube.>>>
>Then you'd better go purchase a KWM2. ;-)
Actually Tom, I come pretty close to that.. my FT-102 is rated at better than -40db. With power reduced to 65 watts the 3 6146s are almost in to a Class-A condition.>>

When is the last time you measured IM in any rig? -34 single tone puts it about on par with an 80A being run hard IF it does what you think.

<<It's not just a "bandscope"..
It's a Tectronics 564 storage oscilliscope, with a 3B3 timebase and a 3L5 Spectrum Analyzer (with a mixer) connected to the output of the two receivers. When I hear buckshot on a signal I can tune it in, set the scope to "store" and in a few seconds have a pretty good picture whats going on. The only limitation is that the signal has to be fairly strong.>>


So it shows you what the guy is actually doing in his shack?? Must be a web cam then!! Smiley

Seriously, I have new test gear like a current Agilent analyzer with good digitized storage, and making an off the air measurement is almost impossible. Especially when I try to do it off the IF of a receiver!!!!! Measuring an IF port is next to useless.

Tom Wrote:
>>I really don't think either you or some "unknown" WB4 can trump Eimac's own engineers.

Tom, Did you look at the link I sent?? It isn't just some "unknown WB4" saying something... the link takes you to the ACTUAL EIMAC DATA SHEET published BY Eimac.

I have data sheets. I don't need to go web crawling to see them.

The data sheets are NOT final operating sheets. They are typical operation of what generally was a sample of one unit in a large fixture at Varian. What YOU keep ignoring is the IVS ratings were approved by Salt Lake, as was the manual. Eimac had no problem with it, neither have customers.

Eimac and other manufacturers very often approve modifications of operation outside typical guidelines.

How many amps have you designed? How often have you talked to Eimac's engineers about IVS ratings?

73 Tom
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« Reply #28 on: November 25, 2003, 02:56:03 PM »

There is some SUPER info here.

I just wanted to share aomething about 3-500s....

When I got out of the Navy, I worked nights in a steel mill while I put myself through College. We made saw blades, using some monster induction hardening machines. One day, I happend to start BSing with the tech that came to the plant to do PM on the machines. He was replacing all the tubes, yep, BUNCHES of 3-500s. No testing, just wholesale replacement after X # of hours. I asked him what he was going to do with them. "Pitch 'em" was his reply. "Can I have them?" says I. "SURE!!". This was in 1969, and although I was a ham, I didn't even know what the tubes were.... After I got home did I open up the Handbook and there were some 6 M amps using this tube. I had a whole BIG box full. All Eimac. I never got around to building an amp, and used the tubes as barter for other 'stuff'. And yes, the tubes were good. A friend (now a SK) built many a 6M amp using those tubes. One was in QST......
You can tell that this was LOOOOONG before E-Bay. ha ha


ron

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