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[Articles Home]  [Add Article]  

ALC, Keying, and Other Amplifier Problems

Alan Applegate (K0BG) on January 26, 2007
View comments about this article!

ALC, Keying, & Other Amplifier Problems

For some reason, there is great confusion about interfacing amplifiers to transceivers, especially legacy models of both. Part of the problem is the popular amateur press, as often seen on these very pages. These admonishments often contain anecdotal information and personal preferences. Further, most respondents have never owned the equipment in question, so their advice is based on what they have owned or used. Thus, some suggestions result in a costly mistake being made.

The first place you should look for interconnect information is in the associated manuals of the equipment you're trying to interface. If you don't have manuals, buy them! There are dozens of places on the net to buy and/or download amateur radio equipment manuals. The URLs appear almost daily within these pages. However, the typical scenario is a late model transceiver with a legacy amplifier. In these cases, in order to safely interconnect them, requires you to know a little more about than what's typically in the manuals.

Relay Keying

Far to many late-model transceivers do not contain a relay to control an amplifier. When they do it is usually not adequate for legacy amplifiers (sometimes not even for new model amplifiers). The requisite open-key voltage maybe exceed (or peak to) 100 volts, and might be negative or positive depending on the model. Most late-model units are just 12 volts, but sometimes the current requirement exceeds one amp, typically twice the maximum current allowed.

Most legacy transceivers can easily key a late-model amplifier, but the reverse is not always possible. This is where a keying interface makes a lot of sense. Both AmpKeyer and Ameritron (and others) make transceiver/amplifier interfaces which will interconnect just about any transceiver to any amplifier.

There are a few companies who manufacture kits to be added to legacy amplifiers to reduce their keying requirements. This might be okay if your transceiver has a relay, but if you own an Icom IC-706 for example, you'll still need a keying interface of some kind.

One important item to keep in mind when using any keying interface is this: The ALC voltage is unbuffered. That is to say, what ever goes in, comes out. Remember this when reading the next section.

ALC

ALC, which stands for Automatic Level Control, is essentially a feedback circuit (internally and/or externally) which gain-limits one or more stages. Its purpose is to prevent over driving the finals as well as any attached amplifier. Due to design considerations of most legacy tube-type amplifiers, the first ALC output circuits (which started to show up in the late 60s) were negative going. That is to say, their resting output (no ALC) was zero. As overdrive was approached, the ALC voltage starts going negative, thus lowering the transceiver's drive (output power). The ALC output voltage may range from -6 to as high as -100 volts.

Most amateurs erroneously believe that all amplifiers require 100 watts of drive. Since this is all their transceivers deliver, many don't bother with the ALC connection. The truth is, most tube amplifiers only need about 65 to 80 watts for full rated output, and a few just 40 watts. Some solid state designs require no more than 25 watts. In any case, over driving results in excessive IMD, manifesting itself as splatter and distortion. Just for the record, unless you own a laboratory-grade storage scope, and know how to use it, you can't see the distortion caused by overdriving. In other words, if you're using a station monitor scope, or an ALC indication to check for distortion in your transmitted signal, you're kidding yourself!

Nowadays, the ALC output supplied by most late-model amateur power amplifiers is between -4 and -20 volts, which is about perfect for most late-model transceivers. For example, an Icom IC-746's output power will drop to nearly zero when the ALC input exceeds -4.5 volts. This presents two problems.

First, while -4 and -20 volts range is correct for late-model transceivers, it is not enough for some legacy transceivers like a Kenwood TS520 or Heath SB102. There is no easy way to correct this particular malady.

The other problem is, the ALC output voltage of some legacy amplifiers can be as high as -100 volts. Apply this to the ALC input port of a late-model transceiver, and you'll have a melt down! Thankfully, the current requirements are low, so a series 10k ohm resistor and a 5 volt zener diode is all you need to protect yourself in these cases.

To be sure, the ALC output pot on the amplifier (if there is one) should be turned to its lowest setting (no ALC output) before doing any interconnections or adjustments. This is true regardless of the age of your amplifier. In any case, the ALC adjustment procedure for your particular amplifier should be followed. Remember, proper use of ALC will increase the average talk power without overdriving the amplifier.

There are almost as many ALC adjustment procedures as there are amplifiers. For example, no two Ameritron amplifiers have the same procedure. This is another reason why it is very important to have manuals for your equipment. In simple terms, the ALC should be adjusted to limit the transceiver's output to the maximum the amplifier is designed to handle. With very few exceptions, this is less than 100 watts!

How Much Drive

It seems to be common practice to drive one's amplifier right to the ragged edge and beyond, and then wonder why the finals died after just a few hours of operation. Add in the fact most users don't know how to tune one, or take way too long to do so, and tube life can be measured nearly in minutes.

One of the more popular amplifiers these days is the four tube, Ameritron 811H (and the 811 3 tube model). If you care to read the manual, it says: This amplifier is designed to operate at full ratings when it is driven by an exciter that has approximately 70 watts (55 watts for the 3 tube version) of RF output. You can use an exciter that has lower output power, but the amplifier's output may be less. If you use an exciter that delivers more than 70 watts, carefully adjust the driving power to avoid "over drive" and the creation of spurious signals, which could create needless interference to other operators. Pay no heed to this statement, and you'll be buying new finals.

Speaking of which, it's all the rage these days to replace the 811As with 572Bs which have more plate dissipation (they also have more plate capacitance which effects tuning in some cases). The general thought is, now that the plate dissipation is about double, you can drive the amplifier with more power. Wrong!

The power supply in these amplifiers, is minimal at best. Overdriving not only taxes the finals, it also taxes the power supply. Factually, it doesn't make much difference which is which, the net result is increased IMD products which cause splatter and distortion.

Hand in hand with this, is the belief that 20 or 30 more watts will magically garner that rare DX contact. It won't! The amount of power increase it takes for a receiving station to notice any real difference in signal strength is about 3 dB. In the case of the 811H, that's equivalent to about 1,100 watts out. The only way to achieve this amount of power increase, is to trade the 811H in on an Al-572!

Tuned Inputs

A lot of the legacy amplifiers do not have tuned inputs. Depending on a lot of factors, this fact may or may not be of concern. When it is, placing an antenna tuner between the transceiver, or using an internal one, to match the input impedance is wrought with problems.

So is using an amplifier without WARC band coverage. While the input tank (if it has one) may be adjusted, the final tank may not have enough bandwidth, and there is almost no way to tell save for reduced output which results in heating up the various final tank components, to say nothing about the finals. And it doesn't address any spurious emissions which might occur.

Finals

Some of the tubes used in legacy amplifiers are no longer available, or are VERY expensive. Eimac 8874s, and all of the various sweep tubes are in this category. As a result, a lot of tube substitution goes on. Like every coin, there are two sides to this.

If you know what you're doing, tube substitution may be the only salvation for that much-beloved amplifier you've owned since high school. Virtually, it requires redesigning the final tank circuitry, changing tube sockets in most cases, and having the necessary tools as well as the knowledge to use them. It is not a job for the uninformed, or faint hearted.

Far too often, folks just stick in a substitute and pray for the best. While it may indeed put out power, you have no clue how clean it is. As stated previously, it takes special laboratory equipment to measure IMD. Meters and on-air assessments are meaningless.

Another inane, ill advised, and selfish act, is deliberately modifying the drive and/or bias of the final stage of an otherwise properly operating transceiver to get a few more watts out. The net result is to drive the finals past their linear response curve which creates additional IMD products that can be clearly heard.

The Presumption of Power

Why amateurs (especially neophyte ones) think they just have to have POWER to make every contact is beyond me. If I may be so brash, I think it is the CB inheritance a lot of us share. This manifests itself in the need to use compression as if it were a necessity, replace otherwise decent microphones with ones enhanced with parametric amplifiers, and driving their amplifiers way beyond reason. As my good friend Steve Katz, WB2WIK/6, would say, "All knobs to the right."

The use of compression is a double edged sword. Properly adjusted, using a well-matched microphone in the proper manner, will indeed boost your average to peak power. If you're already on the verge of overdriving your amplifier, the use of compression will certainly put you there, and unless someone complains about your splatter, you'll never know.

Part of the problem is rooted in these simple facts: Built in metering is universally inaccurate; Most after-market wattmeters aren't much better than built in ones are, including and especially peak reading ones; And a total lack on understanding of the ratio between average power and peak power.

The very best of wattmeters are typically rated at 5% of full scale reading. For example, if the scale you're reading from is 0 to 200 watts, and the actual power is 100 watts dead carrier, the reading could be from 90 to 110 watts and still meet specs. Wattmeters of this accuracy are upwards of $500, and some as high as $1,500. What's more, use one on the edge of its frequency range, and all bets are off. Therefore, you can't rely on a meter to indicate overdrive, and the resulting splatter and distortion.

Regardless of the meter's ultimate accuracy, using one to measure SSB peak power isn't much more than speculation. Individual speech patterns, meter dynamics, transmitter dynamics, an amplifier's dynamics, compression settings, microphone gain settings, and even the background noise level will all effect the reading. And contrary to popular belief, a monitor scope won't help either. Nor will any rule of thumb.

This is to say, if we knew the actual SSB peak power was 100 watts, our non-peak-reading wattmeter might read from 10 to perhaps 40 watts. Wattmeters with peak reading ability are under the same constraints, so their reading aren't the ultimate either. This said, they can be of benefit if for no other reason than to indicate that there is a real difference between average and peak power, or at least should be. If there isn't, it's a sure bet the knobs are turned too far to the right!

Tuning the Beast

It is not uncommon to hear someone tuning up for what seems like hours, striving to get the last ounce of power out. The fact is, tuning an amplifier shouldn't take more than 30 seconds, and if you've done it before, even in less time. And remember this; Improper amplifier tuning is the single most prevalent cause of component failures, especially in minimally sized amplifiers like the Ameritron 811H.

If you don't know the proper procedure to tune your amplifier (perhaps even if you do), you need to read this: http://www.w8ji.com/loading_amplifier.htm

What's more, you should print out the page and put it in your manual as reference material. Pay particular attention to the second paragraph in blue print, and the last paragraph.

Spares

While a little off the subject, this is another consideration to keep in mind if you own a tubed (or solid state) amplifier, especially a legacy one. Over the last 20 years, the number of final types suitable for amateur service has declined to the point you can almost count them on one hand. With very few exceptions, most currently available ones are made in Russia and/or China.

If your amplifier uses 3-500Zs, 811As, 572Bs, 6146s, 8877, or 3CX800s, I don't suppose you have to worry about spares, yet, but this will not always be the case. Sooner or later, they'll all go the same place 8874s and all of the sweep tubes have gone.

Conclusion

Unfortunately, the real people who need to read these lines, won't. The best the rest of us can do is set an example by operating moderately and courteously.

Alan Applegate, KØBG
http://www.k0bg.com

Member Comments:
This article has expired. No more comments may be added.
 
ALC, Keying, and Other Amplifier Problems  
by KF4HR on January 26, 2007 Mail this to a friend!
Alan, your tips are right on and luckly for me; timely. I'm planning on wiring up an Alpha 78 to an ICOM 756ProII here soon and relay keying and ALC are two of my major concerns... (well, that and the condition of the three 8874's! hi). Luckily I have the manuals on hand for both pieces of equipment.

Thanks for taking the time to write this article and if you have any specific experience or information about mating these two pieces of equipment, please let me know. kf4hrkf4hr@yahoo.com Tnx.
 
ALC, Keying, and Other Amplifier Problems  
by K9OSC on January 26, 2007 Mail this to a friend!
Excellent article. Thanks!
 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 26, 2007 Mail this to a friend!
Good artical. Thank you for taking the time to write an artical of substance.

My favorite mis-conception(learned the hard way) is thinking that a rigs built in ATU should be able to tune ANY amps input.

Sad result:Blown finals in the rig. The 80M input coil is toast.

Heath amps are great. However one does need a few mods to work many of todays solid state rigs.

It is not PLUG-N-PLAY.

I really liked my SB-230....25 years ago. I built it in a few days. A single 8873, no fan, a 50 ohm resistive input on all bands(no input coils, resistors are used). I gave it to a school chum. He never paid me for it. KARMA is real. He blew the 8873 after a few years of use.(or so he claimed).

I hope with the influx of new HF users(2/24) that they will read up....before tuning up!
Check out what an 8873 sells for today.
 
RE: ALC, Keying, and Other Amplifier Problems  
by AA4PB on January 26, 2007 Mail this to a friend!
Good job Alan! I might add that the amp should be tuned into a dummy load. If your antenna system has a reasonable SWR (1.5:1 or less) only a minor (quick) touch up will be needed when you switch from the dummy load to the antenna. There is no need to put 30 seconds of dead carrier on top of someones ongoing QSO.
 
RE: ALC, Keying, and Other Amplifier Problems  
by K8MHZ on January 26, 2007 Mail this to a friend!
Yes, many amateurs take too long to tune up their amps.

They also like to do it over an ongoing net.

Nothing says LID like standing on the key for 3 solid minutes over a net in order to tune up a radio or an amplifier.

It happens all the time.
 
ALC, Keying, and Other Amplifier Problems  
by KC8JX on January 26, 2007 Mail this to a friend!
Alan - Excellent. Great job of explanation; a well worth read. 73, Larry KC8JX
 
RE: ALC, Keying, and Other Amplifier Problems  
by KE3HO on January 26, 2007 Mail this to a friend!
Good article Alan. Thanks.

I want to comment on the ALC issue. It is important for people to realize that when the ALC become active (that is, when it reaches a voltage that causes the exciter to reduce power) the result is compression, just like using a speech processor or other compression scheme. That is what results in more "average talk power" when ALC is used. I bring this up because, as you said, some amplifiers require as little as 40 watts of drive for full output. If someone connects a typical 100 watt rig to one of these amplifiers and they leave it set for 100 watts output with the idea that the ALC will keep them from overdriving the amplifier, the result will be extreme compression and distortion, just like turning your speech processor up to an excessive level. The ALC line should be connected and properly adjusted as a safety measure to protect the amplifier. However, the drive level of the exciter still needs to be adjusted to the needs of the amplifier in use. Turn the drive up just enough to just brush up against the ALC active region on voice peaks, no more. If you need more "talk power" turn on your speech processor and adjust it for modest compression, or if you don't have a speech processor, turn the drive up just a little to get a little more ALC action on voice peaks. Don't leave your rig set for "max burn" and rely on the ALC to cut it back unless your amplifier really requires 100W for full rated output. If you rely on the ALC to turn your rig back from 100W to 40W (or even 65W), distortion will result.

73 - Jim
 
ALC, Keying, and Other Amplifier Problems  
by WS4Y on January 26, 2007 Mail this to a friend!
Your articles are always good Alan and this one is
very good. I bought a package of colored stick on
dots and cut them into little sharp pointed
triangles and used them to mark the plate tune and
load controls on my amp. Use a different color for
each band and stick a matching color on the band
switch positions. As long as you continue to use the
same antenna on a band and hang out on about the
same area in the band they will work keeping
undesirealbe carriers off the air. Just check your
watt meter on your first transmission to make sure
it all is well. I am glad you mentioned the AmpKeyer.
I use one to interface a 756 pro II to an old TL-922A.
Use the mosfet output for the fastest switch time for
no swr spike on leading dit.
 
RE: ALC, Keying, and Other Amplifier Problems  
by KD5PSH on January 26, 2007 Mail this to a friend!
Thanks for posting this. The amp makers are incredibly dumb about providing useful information and the radio makers are their equal. One might think that they would see better business if they took better care of customersd; but not so.
 
RE: ALC, Keying, and Other Amplifier Problems  
by W4LGH on January 26, 2007 Mail this to a friend!
well Alan, You pretty much hit the nail on the head with this one. I hav tried explaining this many times and it usually falls on deaf ears. I have a really nice SB-220 that was brought to me for repairs. After opening up, I inquired as to what happened to it. I was told he sold it to a CB'er whe was driving it with...now get this... 600watts! When asked why anyone would do this, I was told, "well @ 100w it put out this much, @ 200w it did this, so I decided to see what I could out of it!"

On the popularity of replacing 811A with 572B, yes the plate capistance is slightly different, but the AL-811 will usually tune it ok. Contrary to popular belief, it will NOT gain you any additional POWER, but will give you a set of tubes that will last a lifetime if used properly. People just don't seem to understand that you have to put POWER in to get POWER out, and I am NOT tallking about DRIVE, I am talking about Plate voltage and current! I did do a mod on the AL-811 and up'ed the plate voltage to 2200v with a different xformer, few other mods and had a 3 tube 811 putting out about 850 clean watts, but why bother?
The difference from 600 to 850 would never be noticed, except on the watt meter. However I will say that running an Ameritron AL-811 @ 600watts is pushing the hell out of it! Its more suited for around 500watts if you want the tubes to last more than 6months! I have noticed that Ameritron on their smaller amps, like to rate tham at the absoulte MAX power. This practice seems to hold true until to get to their AL-82 / AL-1200 or AL-1500 amps.

Another really nice keying interface is made by K4AVU and is completley self contained! You can order it off my website http://www.w4lgh.com . I do not get anything for this, just helping the guy out, and it is a nice product.

Many other things can be discussed about amplifiers and why they are called "LINEAR", Duty cycles, etc, but we can save that for another time.

73 de W4LGH - Alan
http://www.w4lgh.com
 
RE: ALC, Keying, and Other Amplifier Problems  
by WI7B on January 26, 2007 Mail this to a friend!

Alan,

Great article. I think not enough could be said about overdriving amplifiers through inappropriate use of transceiver DSP. As exciter drive to the amp depends on the band to which you are tuned, so does DSP adjustment to avoid voice distortion. ALC alone does not solve the problem in tubed linear amplifiers.

73,

---* Ken
 
RE: ALC, Keying, and Other Amplifier Problems  
by W4LGH on January 26, 2007 Mail this to a friend!
The popular Ameritron AL-811 and the H model are nice amps, but highly over rated on output. The Al-811 is a 3 tube amp and the H model has 4. So the specs stated below would be multiplied by eith 3 or 4, depending on what model amp you have...

Class AB2 Grounded-Grid Operation, this is how BOTH of the AL-811 amps are setup...

Even though Class AB2 cathode-driven/grounded-grid operation produces grid-current, it is never the less fairly linear due to the laundering effect of negative-feedback. This is the result of the input and output signals being in series with each other and out of phase. Due to the negative-feedback, the distortion level in Class AB2 grounded-grid service is low--typically about 40db below PEP.

High-Mu triodes work well in Class AB2 grounded-grid operation. Medium-Mu triodes can be used, but they have less power gain. Tetrodes and pentodes usually work well in grounded-grid operation. Since tetrodes and pentodes typically have a grid-to-screen amplification factor of about 5, its easy to assume that they offer an advantage over triodes in Class AB2 grounded-grid operation. However, RF-grounding the grid and the screen stops grid-to-screen amplification. Applying DC screen-voltage does NOT increase gain because grid-to-screen amplification can not take place unless input signal voltage is applied between the grid and the screen.

The MAXIMUM available power in Class AB2 is roughly DOUBLE the anode-dissipation rating. (811A plate disp is 65watts!)

Originally the 811A was rated at 45 watts plate dissapation, but this was running it in a constant carrier mode (AM), and when everthing went to SSB mode the rating was raised to 65watts. Now using these figures, your AL-811 has 3 tubes, 65watts X 2 = 130watts x 3 = 390watts. Running this power level your tubes will probably out last you! Now the H model with 4 tubes, 65 x 2 = 130 x 4 = 520watts. Now these are absolute max rating from the original tube manufacture RCA. Now also running these amps to these levels it will remain linear, with very little distortion. Now I know what you are gonna say...I have seen over 600watts out of my AL-811, and you probably have with somewhere around 90 to 100watts of drive. At these levels you are driving the amp out of linearity, which injects distortion and can also create splatter. Maybe someone has accused you of splattering on them 3kc away when everyone else in your group was running 2 and 3 times the power you were. Now you know why!! Next time try cutting your drive back and runing the amp around 400watts, no one will notice any signal difference, but WILL tell you how much better you sound. Remmeber @ 400watts thats 6db gain over your 100watt radio, and amounts to about 1 S-unit higher at the receiveing end on a calibrated S-Meter.

Don't take my work for it, Try it! Your tubes will last forever, your amp will run very cool, and no one will ever know the difference.

73 de W4LGH - Alan
http://www.w4lgh.com


 
RE: ALC, Keying, and Other Amplifier Problems  
by W6TH on January 26, 2007 Mail this to a friend!
.

I never had a alc or tuning problem with my Press Wireless 40 Kw output transmitter.

I never had a problem with alc or tuning problem on my 2 1/2 Kw output RCA transmitter.

No problem with my 5 Kw output collins transmitter.

I never experienced a tuning probem or alc problem with my Heathkit SB 200.

As a matter of fact, never had problems with any ham radio gear especially splatter across the band, bands.

Here is an old trick: Tune your amp on low power and then to go for the higher power, just increase the drive power until the amp reaches its peak output, back of a knats hair, stop there, and you are in good shape to transmit...( No need for alc control).

.:
 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 26, 2007 Mail this to a friend!
W4LGH, 600w in! Sounds like you got a very similar amp than I got off of ebarf. It had whacko-jacko mods. A special 11M output tap was in the band switch. I had to almost rebuild the amp from scratch. Heathkit manuals are good for that.
I am in awe of how much punishment 3-500z's can take.
Albeit grid to cathode shorts can happen, if the tube has been dropped.


The amp I purchased used is HL-2200. It is really just a SB-220 with a nicer paint scheme.

When I got it.....ouch. I did fix it. I am fixing it again because the filiment xformer had a meltdown. It smoked up my shack so bad, the fire detecter went off.

I got lucky. I found a new filiment xformer for $50.
I am building the Harbock power supply for the HL-2200. A major improvement for $30.
No more zener diode bolted to the HV containtment. 1%-5% resistors are used for the meters. The rectifiers are 3 amp.

I am looking at a few ALC circuits to use for it.
I will optocouple the TX line.

Beware of so called slightly used or just pulled 3-500Z's on ebay.
 
RE: ALC, Keying, and Other Amplifier Problems  
by K6AER on January 26, 2007 Mail this to a friend!
Alan,

Thanks for the timely article. With a new crop of HF hams coming to HF this information is needed.

I have found that connecting the ALC on today’s transceivers is no longer needed. Transceivers built in the last ten years have excellent power control and if you set the power output to 50 watts the power output will not exceed that level. I won’t matter where the microphone gain or compression your power limit stays at 50 watts.

Connecting the ALC output from the current crop of amplifier with negative outputs from -4 to -20 volts at rated output will shut down many of the new radios. Their ALC inputs are very sensitive and the transceiver output can be shut down with as little as -1.5 volts. All of this is a moot point for the ALC connection is not needed unless you are running an older tube type radio or a radio with poor output power limiting.

As for after market watt meters most are at best some what accurate for CW but their peak reading modes can be off by quite a bit unless they have sophisticated active circuitry such as the Alpha 4510 series, LPG-100 and the Array Solutions unit. This units have microprocessor controlled sampling and are at worst +/- 5% and in the case of the Alpha units are +/- 2% in accuracy. The only other way of reading peak wattage is with a spectrum analyzer with a peak reading hold function. I have compared the above watt meters with several of my spectrum analyzers and they are all very accurate and would be a good investment if you are running an amplifier.
 
RE: ALC, Keying, and Other Amplifier Problems  
by KE3HO on January 26, 2007 Mail this to a friend!
<<< Here is an old trick: Tune your amp on low power and then to go for the higher power, just increase the drive power until the amp reaches its peak output, back of a knats hair, stop there, and you are in good shape to transmit...( No need for alc control). >>>

That's an old trick for destroying an amp. Do NOT tune your amp at low power and then turn the drive up and operate. ALWAYS tune your amp at full rated output. Even if you want to operate at less than full output, tune at full output, then back the drive down.

73 - Jim
 
RE: ALC, Keying, and Other Amplifier Problems  
by W4LGH on January 26, 2007 Mail this to a friend!
Its NOT my SB-220! First off I would NEVER sell an amp to someone who didn't have a license. Nor would I sell an amp to someone who didn't understand how to operate it.

Another thing that was NOT discussed on here about Hi-Power Amp is the Lethal Voltages and current in them! A lot of people will NOT pay attention to the warnings but let them get across 3500volts @ 1amp, an dif they live, it WILL be an experience that they will NOT forget!! And just because you have turned it off, and unplugged it, the caps can hold a charge for a pretty good while, especially on the one where they have removed the bleeder resistors!! Why they are doing this new MOD is beyond me!!

Even the smaller amps like the AL-811 has 1700volts @ 600ma, and this will get your attention as well! So be sure to BE SAFE when messing with amps. They will hurt you, some with perminent damage or death!

73 de W4LGH - Alan
http://www.w4lgh.com
 
ALC, Keying, and Other Amplifier Problems  
by KE7AKS on January 26, 2007 Mail this to a friend!
Now this is why I believe in eHam.net. Nice article written so that MOST folks can use the information.
Thanks for sharing.
73
Harv KE7AKS
 
ALC, Keying, and Other Amplifier Problems  
by NORTHCOUNTRY on January 26, 2007 Mail this to a friend!
The answer to many of the issues raised is simple.

Keep in mind thats why they call it "amateur" radio if you think its anything other than "amateur" radio your kidding yourself!
 
RE: ALC, Keying, and Other Amplifier Problems  
by W4LGH on January 26, 2007 Mail this to a friend!
~"Keep in mind thats why they call it "amateur" radio if you think its anything other than "amateur" radio your kidding yourself."~

This is very true, but many of us have been & are involved with electronics and communications Professionally!! Amateur radio has the same circuits and works the same way!!

Read and Heed, or feel the need! Its OK to ask for HELP! Everybody had to start from the begining once and many a lesson can be learned from someone who's been there done that. I am sure many of you have said it to yourself over and over before, "Why didn't I listen to my Parents!" Same applies here too!

Another saying comes to mind.."Hard Heads have to FEEL!"

73 de W4LGH - Alan
http://www.w4lgh.com

PS..A lot of GOOD accurate info has been discussed here. One can learn a lot by just reading and keeping an open mind!

 
RE: ALC, Keying, and Other Amplifier Problems  
by N6AJR on January 26, 2007 Mail this to a friend!
Nice article and very well written. good JOB.

I never us an ALC line, on one of my older amps ( a Clipperton L I think) when I hooked up the ALC line the amp would "motorboat" and cause distortion, so I learned to tune my amp and limit the input my self. I still to this day, and do not use ALC on any of my amps including the alpha 87 A. I tune for max power out, at my chosen power level, and then check the dip and peak . the dip/peak and max output power are the same.

Also I always use a dual cross needle meter for tuning an amp. this way you don't have to push in and set, pull out and check, you get foward, reflected and swr all at the same time.

Also I tune for max power out then back the drive down just a touch. this is so the tubes are never working at maximum smoke for all the time they are on. The fellow on the other end will never hear the difference between 1500 watts and 1450 watts, but the tubes will last for years. really.

the last comment I have is using 572's in place of 8 11's. save your money. I have yet to burn up an 811 tube on an amplifier. they last years if you don't try to get every last erg of power out of the amp. and if you go to MFJ you can buy a set of 3 811's for $60 or you cna buy one 572 for $60. so you could retube 3 times for the price of 1 set of 572's.

I do have a box here with a dozen 572's, a dozen 811's and a bunch of 6146's and so on in it. that I bought for spares over the years. I have yet to use one.

 
RE: ALC, Keying, and Other Amplifier Problems  
by N6AJR on January 26, 2007 Mail this to a friend!
Nice article and very well written. good JOB.

I never us an ALC line, on one of my older amps ( a Clipperton L I think) when I hooked up the ALC line the amp would "motorboat" and cause distortion, so I learned to tune my amp and limit the input my self. I still to this day, and do not use ALC on any of my amps including the alpha 87 A. I tune for max power out, at my chosen power level, and then check the dip and peak . the dip/peak and max output power are the same.

Also I always use a dual cross needle meter for tuning an amp. this way you don't have to push in and set, pull out and check, you get foward, reflected and swr all at the same time.

Also I tune for max power out then back the drive down just a touch. this is so the tubes are never working at maximum smoke for all the time they are on. The fellow on the other end will never hear the difference between 1500 watts and 1450 watts, but the tubes will last for years. really.

the last comment I have is using 572's in place of 8 11's. save your money. I have yet to burn up an 811 tube on an amplifier. they last years if you don't try to get every last erg of power out of the amp. and if you go to MFJ you can buy a set of 3 811's for $60 or you cna buy one 572 for $60. so you could retube 3 times for the price of 1 set of 572's.

I do have a box here with a dozen 572's, a dozen 811's and a bunch of 6146's and so on in it. that I bought for spares over the years. I have yet to use one.

 
RE: ALC, Keying, and Other Amplifier Problems  
by WB2WIK on January 26, 2007 Mail this to a friend!
I've made a new silk screen for my front panel, so all the controls that used to go to "10" now go to "11."

This simple modification allows me to crank things up 10% higher.

:-)

Nice article, Alan!

WB2WIK/6
 
RE: ALC, Keying, and Other Amplifier Problems  
by W1RKW on January 26, 2007 Mail this to a friend!
<<<The ALC output voltage may range from -6 to as high as -100 volts.>>>

This is nit picky but don't you mean as low as -100V? -6V is higher than -100V. If from an absolute value then I agree.

Despite that excellent article and responses.
 
RE: ALC, Keying, and Other Amplifier Problems  
by AA4PB on January 26, 2007 Mail this to a friend!
How do I measure -100V ? My analog meter scale doesn't go below zero :-)
 
ALC, Keying, and Other Amplifier Problems  
by N0AH on January 26, 2007 Mail this to a friend!
Alan,

FB report.

But I think some of our new friends moving onto the bands will be confused. They are used to running 12 watts into an amplifier trying to get 100 watts out-

Any suggestions for them because I don't think they have ever seen an ALC control-

One other comment. Why would you refer anyone to a person who is a MFJ design engineer?

That said, I really think you have written an excellent article which I am printing out for my library.
 
RE: ALC, Keying, and Other Amplifier Problems  
by N3JBH on January 26, 2007 Mail this to a friend!
"WB2WIK
I've made a new silk screen for my front panel, so all the controls that used to go to "10" now go to "11."

This simple modification allows me to crank things up 10% higher. :-) "

i bet it is more like 9% heee heee cute steve you should market them 11's

 
RE: ALC, Keying, and Other Amplifier Problems  
by HA6SST on January 26, 2007 Mail this to a friend!
"How do I measure -100V ? My analog meter scale doesn't go below zero :-) "

Easy, turn your meter upside down so the electrons flow the other way.

HA6SST
 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 26, 2007 Mail this to a friend!
I see I am not the only fan of the movie "Spinal Tap"'.

 
RE: ALC, Keying, and Other Amplifier Problems  
by WB2WIK on January 26, 2007 Mail this to a friend!
>RE: ALC, Keying, and Other Amplifier Problems Reply
by HA6SST on January 26, 2007 Mail this to a friend!
"How do I measure -100V ? My analog meter scale doesn't go below zero :-) "

Easy, turn your meter upside down so the electrons flow the other way.<

::Even easier: Just use the meter in a mirror.
 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 26, 2007 Mail this to a friend!
<<<<<<Its NOT my SB-220! First off I would NEVER sell an amp to someone who didn't have a license. Nor would I sell an amp to someone who didn't understand how to operate >>>>>>>


Relax, I think you misunderstood what I said. You had heard about some CB type that pumped 600W into an SB-220.

I said, I think I must have purchased a SB-220 that had the same thing done to it.

The tubes were soft and had burn marks. 2 input inductors were melted. The 10M tap only tuned in the CW portion of 10M. It looked like some "HACK" moved the tap to be optimised for 11M.

The person I purchased it from claimed it was his fathers. He said his father was a ham. He also claimed in the ebay ad, it was fully working.

I paid $575 for it. When I told him what crap he sold me, he gave me $250 off the price.

What was even funnier were many other bidders begging me to sell them the amp for $700. Little did they know what a hack job was done to a good heathkit.

To make a long story short. I got some use of it after rewiring the thing. The filiment transformer blew out a few months ago. The sharks came out offering me $200 for it. They wre hams too.
Good fortune went my way. Found the filiment transformer on ebay. Everybody that tried get it from me for $200-$300 said I would NEVER find a filiment transformer :)

The bleeder resistors work just fine. However I always wait 2 minutes power off, before I short out the remaining charge in the caps.

3000VDC@500milliamps, I think comes close to what the electric chair at sing-sing uses.


 
ALC, Keying, and Other Amplifier Problems  
by KI4DTB on January 26, 2007 Mail this to a friend!
Alan, could you please expand a little on why a station monitor scope will not show over driving or signal distortion. I thought that's what a monitor was supposed to do. Thanks. Doug
 
RE: ALC, Keying, and Other Amplifier Problems  
by K0BG on January 26, 2007 Mail this to a friend!
Some of the treads attached to this article bring (brought) up some interesting questions.

NORTHCOUNTRY posted a question on the amplifier forum (do you use ALC) after he posted a reply here. So that it will get a little more exposure, here is my answer to him:

............. If you ask this question to 100 amateurs, you'll get about a 50/50 split. There are a lot of issues determining what answer you'll get.

Point one: Although tunable tube-based finals have their own issues, they're not too much removed, in most respects, to their solid state equivalents. Generally speaking, a properly designed final tank (amplifier if you please) will have the lowest IMD when running between 80 and 100 percent of their rated output. This includes what you and I refer to as amplifiers (Ameritron 811H, AL0572, or Heathkit SB200 etc.).

Point two: A lot of solid state transceivers have an initial key down power spike as much as double their nominal output peak. Turning the drive down exacerbates this issue in almost all cases. Typically, the ALC is slow enough acting (i.e.: long lag time) that it has no effect on this leading spike.

Point three: Proper use of the level of drive power, and the amount of ALC fed back to the transceiver can increase the average output, and in most cases limit over drive (RF compression as it were). Too much ALC (driving an amplifier with a full-on 100 watt transceiver into an amplifier that needs just 65 watts of drive and using ALC to limit the drive) will greatly increase the RF compression. The result is much increased IMD levels.

Point four: Regardless of popular press, most amplifiers can be over driven with the average 100 watt transceiver. The use of speech compression (no matter how it is done, front panel adjustment of too much ALC) exacerbates IMD. Add in a dose of over drive, and IMD gets even worse.

Point five: With just a few exceptions, most currently available amplifiers have inadequate power supplies, and poorly designed ALC circuits.

The end results is varied depending on the methodology used by any one specific amateur, and the equipment he/she uses. This fact makes it difficult to answer the question whether ALC is needed or not.

Thus, deciding on a ROT (rule of thumb), or deciding whether you yourself should or shouldn't use ALC, is all but moot.

You posted this question after you posted a reply to my article, which leads me to believe you're at odds with my assessment in that article. And you might be correct. But you also might be incorrect.

This is why my suggestion of operating moderately is the only REAL measure. You don't have to do anything but listen on any amateur band to hear what happens if you don't.

So the bottom line is, you're either setting the example, or being one. It is your choice. ...................

Someone else ask about using a monitor scope, and why I thought is was not adequate as an indication of excessive IMD. The short answer is, the response is not fast enough, and even if it was, the phosphor is not persistent enough for you to view the nuances that comprise IMD products.

The longer answer is, it takes a good, laboratory-grade storage scope, and a very good spectrum analyzer. The quality necessary is beyond the average amateur's budget.

I referred readers to a specific page on Tom Rauch's, W8JI, site. If you peruse a few of the other pages, you'll find photos of his "lab". Ask yourself how many folks you know who have this sort of elaborate equipment. I venture to say, not many. Tom's array is what it takes to measure IMD.

so, I'll stand pat on my answer: Wattmeters, ALC indicators, station monitors, run-of-the-mill O-scopes, or on-air reports are not a guarantee of a clean signal. The only alternative is moderate operation. In other words, knobs to the left, not to the right!

Alan, KØBG
www.k0bg.com
 
RE: ALC, Keying, and Other Amplifier Problems  
by K0BG on January 26, 2007 Mail this to a friend!
PS: With a little tongue in cheek...

I suppose when negative voltages increase, they go down. In a similar fashion, when positive voltages increase, they go up. However...

When there is a decrease in positive voltages, they go down. So I guess you could say when negative voltage decreases it goes up.

Perhaps I should have said the value increased, or perhaps I could have said the potential increased. Maybe even the numerical value increased.

In any case, the nit was picked, and I chuckled.

Alan, KØBG
www.k0bg.com
 
RE: ALC, Keying, and Other Amplifier Problems  
by WB2WIK on January 26, 2007 Mail this to a friend!
>ALC, Keying, and Other Amplifier Problems Reply
by KI4DTB on January 26, 2007 Mail this to a friend!
Alan, could you please expand a little on why a station monitor scope will not show over driving or signal distortion. I thought that's what a monitor was supposed to do. Thanks. Doug<

::Many problems with using "monitor scopes" for this; but one is that a regular monitor scope is time domain, not frequency domain, and therefore cannot indicate anything involving spectral purity or intermodulation distortion, at all. A monitor scope can possibly be an indicator of non-linearity if used properly, but to do that involves more than just modulating your transmitter and observing the RF envelope. Even 10% distortion, which is horrific, won't show up that way.

Another issue is most scopes have displays that are just too small to see much. A typical "station monitor" has a 4" or 5" round, square or rectangular display. If the RF envelope occupies the entire display right to the limit lines, when looking for distortion, you're looking at maybe 1/4" of the overall display. Probably from 3 feet away. And probably using a signal that's a moving target. What are you really going to see?

The monitor scope is more useful for double-sideband AM, in that positive or negative peak clipping can be seen immediately, and modulation percentage observed and pretty closely estimated at a glance. SSB signals are different. There's no carrier for reference, and no negative cycle modulation at all.

I have lots of laboratory scopes at home, and the instruments I use most to monitor my signal are a true PEP wattmeter and a pair of headphones connected to a second receiver.

WB2WIK/6
 
RE: ALC, Keying, and Other Amplifier Problems  
by W6OP on January 26, 2007 Mail this to a friend!
Alan, thanks for the great article. Even though I have a solid state amp (THP HL-1.5K) I like to learn about all kinds of amps.

From your responses and others I understand that running my rig at 100 watts and letting the ALC reduce power is the wrong thing to do on a solid state rig, too.

Is that correct?

I have noticed the spike in output power and have adjusted my ALC to compensate. Looks like I have been turning down the wrong control. I should have been turning down my power out from the rig instead.

This is my first amp so I haven't had the experience with all of this like many of you.

Thanks for setting me straight.

Pete W6OP

 
cheap keying interface  
by WR8D on January 26, 2007 Mail this to a friend!
Go to the local radio shack and pick up a 9volt relay, one 9volt battery, one 9volt battery terminal, two rca jacks, a very small project box, some small pieces of wire and make your own interface for about 10-15 bucks. The 9volt battery will last for years, let the rig switch the 9volt relay and let it's contacts switch the amplifier line in and out. Remember to mark the jacks for in from the transmitter and out to the amplifier so you don't get them crossed up. Nothing would happen if you did but it'll look nicer if you mark them. "hi hi". Don't spend 50bucks or more for one of these gadgets you can make in 30minutes yourself and actually say "you've made something". 73 John WR8D
 
RE: cheap keying interface  
by WR8D on January 26, 2007 Mail this to a friend!
I forgot to add the above interface is only for the keying line between the rig and amplifier. It isn't associated at all with anything to do with alc just keeping those sometimes high voltages present at the amplifier keying relay away from the keying relay in your rig. Most newer rigs have a transistor relay setup that will handle a little over 20 volts +/- by using this little 9volt relay the rig never sees over 9 volts, "perfect". 73 John WR8D
 
RE: ALC, Keying, and Other Amplifier Problems  
by KA8OCN on January 26, 2007 Mail this to a friend!
Thank You for your time of putting this article together!
I purchased a Ameritron AL-811 just over a year ago and this article is much better than the manual!

One question I have, I see in some of the replys swr is talked about, I have always tuned my amp into a dummy load is this not correct?

Delbert McCord
KA8OCN
 
ALC, Keying, and Other Amplifier Problems  
by WPE9JRL on January 26, 2007 Mail this to a friend!
Go Blow.

 
RE: ALC, Keying, and Other Amplifier Problems  
by N4SL on January 26, 2007 Mail this to a friend!
Why do you think that writing a tutorial in the derogatory will be well received by the people who need the information the most?

The tone is clearly "Why is everyone so f*&%ing stupid? Why can't they be more like me, perfect and wonderful?"

Off putting to say the least, it seems designed to gloat and scold, not really to inform even though the information is contained within.

Hear that? It's the sound of a bunch of newbies clicking off.
 
RE: ALC, Keying, and Other Amplifier Problems  
by N6AJR on January 26, 2007 Mail this to a friend!
Please Gentle men, if you must be negative, please input what you use for an alternative. I post articles here, so do a lot of the other respondents on this thread.

go blow and arrogance, hmmm, do you have a comment on the subject, or is this just another attempt to kidnap a thread into a "we won" urination competition.

I respect others opinions, and fought for that right, I put my money where my mouth is.

as a Nam vet, and a long time ham, you are leaving a bad taste in my mouth.

please feel free to correct me if I am wrong, but do it with something more than attitude. loudest is not always rightest.....

Thanks for the band width and like I said earlier , nice article Alan. and hey Steve, and Jeff and the rest of the prolific authors.
 
RE: ALC, Keying, and Other Amplifier Problems  
by NB3O on January 26, 2007 Mail this to a friend!
Some of the leading edge IMD spikes from the ALC are too fast to see on my old 8566B when using it's narrow IF filters. The new Tek DPO scopes with large memory and FFT features are out-of-range for most of us, too.
I found a better and cheaper way by running the transmitter RF sample into an old Analog Devices AD9432 evaluation board and dumping the parallel data into a chunk of SDRAM. The stored snapshot is then slowly sucked into a PC through the serial port. The PC does the FFT and graphing (I use Mathcad). The sample clock is triggered by the PTT, so time slices of the start-up spectrum can be easily seen. It takes a CPLD, UART, oscillator and some other small parts for the glue logic, however the CPLD programming tools are free. It's not the fasting thing in the world to download the data into the PC, but it works. For the price less than a pair of 3-500Z's and a few long weekends, the goodies are available to anyone willing to go through the effort.
 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 26, 2007 Mail this to a friend!
A good item t have is an opto-isolated amp to rig coupler for older amps.
Covert 100V TX lines to 5-12vdc. It iss isolated by optical means. L.E.D and a photo-resistor.
 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 26, 2007 Mail this to a friend!
How does the Eham gang feel about in-rush protectors.
When the power switch is on, only 10V is applied for 10 seconds. Then the full 110/220 kicks in.

Some say it prolongs the life of everthing from tube filaments, rectifiers, and filter caps.

Also, the new Harbock power supply board says filament voltage will be 6.8V instead of the usual 5.1V. They claim lower heat during voice lulls.
It seems odd to me. I would think higher filament voltage for my 3-500z's would be diminished.
 
RE: ALC, Keying, and Other Amplifier Problems  
by W4LGH on January 27, 2007 Mail this to a friend!
The in-rush current protection maily protect your AC power switch! Thats the primary gain, then secondary gains are Caps, then tube filaments. The problem with most in-rush circuits are they switch over to fast. I modified on of Harbach's universal boards to give it about 3 second delay, thus allowing the tube filaments a little extra time to warm slowly. As it came the switchover was about 300ms. I am certainly NOT say they aren't any good, but protection is minimal at best. A better design would be to start a 200v amp up on 110v for about 3 seconds before switching to full 220v. It would also be great to do the same when in standy mode, dropping the input back to 110v just keeping the filament warm and a lot less stress on the rest of the amp. I was working on this very mod when I decided it was not a simple deal on the amp that I was experimenting with. Now running the amp on 110v and switching the input jumpers to 200v, thus dropping input voltage in 1/2 was a lot easier.(rc timer & relay)
Another nice trick would be to remove the HV from the tubes in standby, as it does not do them any good
sitting idle with full voltage on the plates.

As for putting 6.8volts on a 3-500 filament, you will distroy the tube in no time! If you go out and read some of the white papers on this tube you'll see why. Since the filament is also the cathode (also referred to as direct heated cathode) the addition temps generated by this voltage will distroy the coating on the cathode in no time flat!! Not to mention that the seal on the base of a 3-500 is good to about 225 degsC.

73 de W4LGH - Alan
http://www.w4lgh.com

 
RE: ALC, Keying, and Other Amplifier Problems  
by W4LGH on January 27, 2007 Mail this to a friend!
PS... Harhach's in-rush mod is good, but needs to incorporate a small fuse in series with the dropping resistors in the event the relay does not switch. The fuse would blow protecting the 10w resistors, maybe preventing a fire, and would give you some idea of a problem with the circuit and where to trouble shoot.
Without this fuse, if the relay didn't switch, the 10w resistors could get hot enough to set the board on fire. Fuses are GREAT little devices, that most people don't respect, not only for adding safety, but also a heads up as to a more serious problem.

Just some more FOOD for thought!

73 de W4LGH - Alan
http://www.w4lgh.com
 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 27, 2007 Mail this to a friend!
hmmmmmm......Yes the 3-500Z is direct cathode.
Here is the Harbach paper, I got It wrong.
1)You will notice reduction in idle plate current.
The new board provides 6.8V of bias for 3-500z tubes,rather than 5.1v by heath,

I read this paper wrong. Of course filiment voltage comes from the filiment Xformer, bifiler choke than filament. Filament voltage should be the same because the Harbock board has nothing to do with filament V.

Stupid me. IT IS IDLE bias of 6.8V rather than 5.1v.

OK, forget that stupid mistake.
Now, I am just going to go with a single 3-500z. Just for testing. Yeah, tuning will be a little different.
I just want to make sure after I practicly rebuild this amp from scratch again.
Only then I will invest in a set of Grafite 3-500zd's
I am still going to run it on 110V. 220 is impossible here. I get 1KW PEP on 20M with old Eimacs. I like to run only 500-700W. Twin 3-500's double as a shack heater for me. Well sitting near the fan anyway.
Harbock was out of the new capacitor bank. That will be next.

I also what to beef up the 150V bias. The diode and cap will be replaced too.

One hand rule does well by me, to prevent electrocution. Or a Michael Jackson single glove coated with neoprene.

I see why beefed up 220's/2200's sell for over $800.
One certainly has a better amp than a TL-922 by kenwood. one dope payed $1150 on ebay.
IMHO, 3-500zd's will be around the longest of all the real RF tubes. Sweeps will be swept away. Only exception are 6L6's for Marshal guitar amps. Somebody has a homebrew amp with 10 6L6's for sale. The price is right $150.



I guess the price of MRF-154's will have to come down in price, before 3K input amps solid state can be sold for less than $2500.
Switching supplies are not the issue. I can get 48V@60A supplies for $600. The Sanyo's come complete with over volt and current limiting. They also have a few power down feed back loops. One could use one of the loops for high SWR.
 
ALC, Keying, and Other Amplifier Problems  
by K6YE on January 27, 2007 Mail this to a friend!
<<< KE3HO on January 26, 2007
That's an old trick for destroying an amp. Do NOT tune your amp at low power and then turn the drive up and operate. ALWAYS tune your amp at full rated output. Even if you want to operate at less than full output, tune at full output, then back the drive down.

Jim, you hit nail on the head. Tuning at low power has been a misconception for many years.

Alan, your article is G-R-E-A-T. Keep up the good work.

Semper Fi,

Tommy - K6YE
DX IS
 
ALC, Keying, and Other Amplifier Problems  
by N0AH on January 27, 2007 Mail this to a friend!
Alan,

I am ordering my MFJ NEATO lab so I can be referred to next. I'll have a photo of it soon on my webpage so you and others can realize my brain is now bigger than a Volkswagon Bug.

I will now design 4,739 gizmo's every ham wants.

I will also use commando tactics to restructure the 30 meter band for God, Mother and Country as I have a flicker of QRN at around 10.101. This DX calling frequency must be changed.

Like Plankton, I will rule the Earth someday- All because I have the new MFJ NEATO lab. By the way, it consists of a card board picture you can set behind your shack! All for only $799.85 with a 12 month warranty.
 
ALC, Keying, and Other Amplifier Problems  
by W8VVE on January 27, 2007 Mail this to a friend!
Alan...a very good article...I've already printed it out and its in my "amp" file. Thanks for your contribution.
Sam W8VVE
 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 27, 2007 Mail this to a friend!
Can somebody enlighten me as to what a "MFJ NEATO LAB"
is?
 
ALC, Keying, and Other Amplifier Problems  
by G8KHS on January 27, 2007 Mail this to a friend!
Very useful article Alan.

A good dummy load is a great asset to the tube amplifier newcomer. You can practice getting your tune up done as quickly as possible to minimise overcooking your output devices. It's also good for getting the hang of plate and load tube type transceivers like the FT101 series.

As you gain confidence, progress to on air tuning keeping the power down at first until you get used to the different characteristics of the antenna.

I know this is all well trodden ground, but there are quite a few operators who are a bit wary of tube linear amplifiers.

So, if you have some amplifier questions no matter how basic, then post your questions on the forums.

Don't be afraid to ask.
There's always someone out there to help you.

73 to all

John G8KHS
 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 27, 2007 Mail this to a friend!
I would rather have a little orphan Annie secret decoder ring and a red rider bb rifle to save the world
from mutant pickles from cold fusion experiments. :)
 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 27, 2007 Mail this to a friend!
I would rather have a little orphan Annie secret decoder ring and a red rider bb rifle to save the world
from mutant pickles from cold fusion experiments. :)
 
RE: ALC, Keying, and Other Amplifier Problems  
by W2IRT on January 28, 2007 Mail this to a friend!
Naw, you'll shoot your eye out, kid!
 
RE: ALC, Keying, and Other Amplifier Problems  
by W2IRT on January 28, 2007 Mail this to a friend!
Actually, I've been wondering something about my AL-1500 since I got it last year. From what I see, it draws about 1A @ 250V in standby. What I'd like to know, especially given the high cost of a new tube, am I better served leaving the amp on for long periods of inactivity or only power it up as needed?

These days, I only work what I need for DX stats, I just don't have the time or inclination to ragchew much. I'm more "get in, make the Q, get out" than anything else. What I've been doing until now is leave the amp off until I need it, then after the Q, I let it sit for about 4 or 5 minutes then power down. The blower on the AL-1500 (default setting) is obnoxiously loud, and my spacious shack doesn't help in that regard, so switching it off seems to be the right move from a noise perspective...but am I risking damage to the tube in doing so?
 
RE: ALC, Keying, and Other Amplifier Problems  
by N2MU on January 28, 2007 Mail this to a friend!
Interesting and thought provoking overview of the subject, and each section could be a topic in subsequent Eham “Articles” at length, but I take issue over posted comments about station monitor scopes.

Certainly, today’s laboratory equipment is better suited for quantization of various distortion components viewed in simultaneous domains, and today’s AD equipment with DSP analysis seems almost like science fiction.

However, monitor scopes and old lab scopes such as Tektronix (mentioned because they are ubiquitous and cheap at hamfests) with a bandwidth adequate to satisfy the fidelity criteria (say 10 times the bandwidth of the frequency of interest like a Tektronix 465 - 100Mhz or 475 - 200Mhz bandwidth scope) of the waveform of interest can provide “qualitative” and in some cases quantitative insight into HF amplifier problems and performance at a glance, to a trained eye. Monitor scopes with direct sampling of the RF for electrostatic deflection provide a reasonable bandwidth too.

By way of example, the Kenwood SM220 monitor scope provides easy access to perform 2 tone, envelope, and trapezoidal tests to the exciter and/or amplifier while on the air talking with your buddies.
Older ARRL Handbooks have pictures of scope patterns resulting from various amplifier deficiencies of biasing, screen grid, drive, non-linearity, etc...

With simple homebrew voltage dividers, sampling the RF outputs from the exciter and amplifier you can develop a trapezoidal test from an “old lab scope” with an x-y deflection setup, that will easily warn you of most of the resulting garbage (“splatter” etc.) otherwise, emitted from an improperly tuned amplifier. It will aid in the ritualistic load and tune procedure and give insight into the right amount of “antenna over coupling,” drive, and ALC (if utilized) needed for dynamic voice transmissions indirectly referred to in some previous posts. Further, you can measure parameters including PEP RF output voltage with reasonable accuracy and thus power output, with a known antenna load.

In short, a low cost scope appropriately sampling the RF should be part of an amplified ham shack setup, and I have some thoughts on preventing hot switching through “non invasive” ALC utilization on certain HF amplifiers, but, I have to go now because someone probably without a monitor scope is messing me up on 40 meters with a 30k wide signal...
73 Hank N2MU ...-.- ..
 
RE: ALC, Keying, and Other Amplifier Problems  
by W9AC on January 28, 2007 Mail this to a friend!
> "Just for the record, unless you own a laboratory-grade storage scope, and know how to use it, you can't see the distortion caused by overdriving. In other words, if you're using a station monitor scope, or an ALC indication to check for distortion in your transmitted signal, you're kidding yourself!"

Good article, but I don't necessarily agree with this statement. I do agree that some forms of distortion are very transient in nature and their measurement requires more elaborate methods than we're accustomed to. But to completely write-off the usefulness of the monitor scope as an *indication* of distortion is not correct.

I use a scope to monitor my transmitted CW waveform. I also use use it in a trapezoid mode to adjust my amplifiers for maximum SSB linearity. Neither purpose results in an absolute measurement. But then, it doesn't need to be. The monitor scope still serves a useful purpose for rudimentary measurements. For example, the scope if useful for ensuring that amplifier hot-switching is not occurring. Oftentimes hot-switching will occur when some part of a timing circuit has failed.

I once hot switched an Alpha 70 amp over the course of several weeks and didn't realize it until it was too late -- the Jennings T/R vacuum relay required replacement. The addition of the monitor scope would have prevented that repair. The solution in that case was to go back into the rig and find a better T/R sampling point that didn't result in the hot-switching of the amp. Without the scope, I couldn't have done that.

Otherwise, excellent points!

Paul, W9AC





 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 28, 2007 Mail this to a friend!
I have a question. I purchased a 3-500z eimac on E-barf.($Question. I recently purchased a used Eimac 3-500z.
The seller says it has full output. (I would test it, but my HL-2200 is on the bench for improvements)

The tube has an unusual look to it. I fully tested the filament and tested for shorts. All test's A-OK.

OK, the tube. The seller did say there was a small burn mark on it.($50 for the tube was a good deal)
On closer inspection, it does not look burned.
What I do see is a silver like coating at the base of the tube.

WHAT GIVES?
 
Soft-start fusing  
by W2CBK on January 28, 2007 Mail this to a friend!
W4GLH is right. This happened to me. After nearly a year without problems, one day I failed to hear the satisfying relay click when I powered up the amp. I switched it off as quickly as possible, but not quickly enough. A flash was seen, and thick smoke poured out of the amp. The resistors and board were charred. The smell persisted for some time. Thankfully, the fire was confined to the board.

A call to Harbach's resulted in surprise on their end--I was assured that the relays last virtually forever. I ordered a new soft-start board which has worked flawlessly for five years.

Fuses would have prevented this event. I plan to add tthem ASAP.
 
ALC, Keying, and Other Amplifier Problems  
by ZENKI on January 28, 2007 Mail this to a friend!
SM5BSZ has been writing about these ALC issues for years
now. He goes onto say that ALC produces a lot of adjacent channel interteference, splatter and keyclicks.

You can read that all ham radio rigs ALC's have design problems before we even consider the radio too AMP alc line connection.

http://www.sm5bsz.com/dynrange/alc.htm
The Abdominable ALC!!!!
 
RE: ALC, Keying, and Other Amplifier Problems  
by K4RAF on January 28, 2007 Mail this to a friend!
I use a low cost relay made by W2ENY for almost all amps I have here, including SB-220, Henry 2K & Alpha 78.

They work fantastic, are low cost & Bob's service is quick for less "shipping" fees... All his electronics is contained in the shell of the connector. Nice & neat!

He can be reached at w2eny@yahoo.com & tell him K4RAF sent you!

K4RAF
wifidx@gmail.com
 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 29, 2007 Mail this to a friend!
Just a thaugt. The FCC says we must use manual keying, no rf sensing relays. Every body runs a wire between a rig and amp. Many times, the keying schemes do not match. Like using a Heathkit with a FT-100D for example.

It is very easy to design a wireless link or infrared
link for the Amps key down relay.

One has one less wire to run. On never has to put a softkey in the amp.
The same would work for alc. Only telemetry is transmited.

 
RE: ALC, Keying, and Other Amplifier Problems  
by WA2JJH on January 29, 2007 Mail this to a friend!
K4RAF, what is special about the relays made by your friend. I am just interested. What makes those relays
outstanding?
 
RE: ALC, Keying, and Other Amplifier Problems  
by N9AOP on January 29, 2007 Mail this to a friend!
I like using an O-scope to monitor my amplifier loading and also microphone drive. Lot of folks out there drive their mike like some did in the good old CB days where you just had to crank up that power mike. Also, as was said before, get a manual - they are available and follow it.
As far as ALC - some new transceivers and amplifiers don't do it, ie. TenTec.
 
RE: ALC, Keying, and Other Amplifier Problems  
by N9AOP on January 29, 2007 Mail this to a friend!
I like using an O-scope to monitor my amplifier loading and also microphone drive. Lot of folks out there drive their mike like some did in the good old CB days where you just had to crank up that power mike. Also, as was said before, get a manual - they are available and follow it.
As far as ALC - some new transceivers and amplifiers don't do it, ie. TenTec.
 
ALC, Keying, and Other Amplifier Problems  
by WX1F on January 30, 2007 Mail this to a friend!
It took you a couple of paragraphs to squeeze it in but you did finally figure a way to make your usual derogatory comment about CB radio operators. No matter how entertaining and informative your articles are, it seems you have to brag at least once and degrade CBers at least once. Those of us with radio roots in CB and/or a limited knowledge of your vast vocabulary commend you for holding it down to only one of each this time. (It took me a second or two to figure what you meant by the term "Legacy". What the heck is wrong with using the word "older") Yes...I too, heard a loud "click" from the newcomers.
 
RE: ALC, Keying, and Other Amplifier Problems  
by KI6LO on January 30, 2007 Mail this to a friend!
Alan,

Good article. Lots of ideas to be aware of. Nothing worse than listening to some bonehead lid trying to tune their amp for minutes (once listened to a jerk for almost 5 minutes) on top of a DX pileup. Really irritating and shows no operating skills at all.

One thing that I like to do with tuneable tube gear like xcvrs and amps is to make a set of small stick-on markers that I put on the tuning scale of the amp at the proper tuning positions for each band. I only need to PROPERLY tune the amp once (into a dummy load and then a quick tweak into the actual antenna), mark the dials with the stick-on markers and it's all set for instant recall later. Closest thing to solid state you can get without actually having it. Band changing is as easy as resetting dial to the correct markers for the selected band, a quick short transmission (under a second or so) to check and I'm all set.

I make the stick-on markers out of colored electrical tape and place a similar piece on the bandswitch. Simple as setting all dials to the color for the bands desired and go for it. One could also make multiple sets of markers for different antennas so each is accurately tuned for any given band.

Best thing is they are easily removed for different antenna setup or if selling the gear - no marks or scratches on dials to cause loss in value.

Gene KI6LO

 
RE: ALC, Keying, and Other Amplifier Problems  
by WA4DOU on February 4, 2007 Mail this to a friend!
Good article Alan!

The CCS rating of the 811A made by RCA was 45 watts and they rated it at 65 watts ICAS.I have seen at least one reference,by a Chinese manufacturer,to its tube being rated at 40 watts CCS. Therefore its ICAS rating is no more than 60 watts.When operated in an amplifier using four (4)
such tubes,the combined plate dissipation rating is 240 watts.This assumes that the tubes are matched and share the load equally.

Ideally,one would call on these tubes to produce an output of no more than about twice the plate dissipation rating,in the case of four (4) tubes,about 500 watts.Three (3) tube amplifiers,about 375 watts.Power input to the tubes would be about 770 and 577 watts respectively,assuming a plate efficiency of 65%.In ssb and cw service,the tubes would be dissipating heat at a lower rate than their specs because ssb is a low duty cycle mode of 25-35% and cw about 50%.In such service the tubes would provide long life.

However, recognizing that the "average" heating of the plates is perhaps only 35% of 240 watts in the ssb example above and 50% in the cw example,the designers/manufacturers"push"the tubes to higher power levels.After all,in ssb service the average power dissipated is 95 watts and in cw service its 135 watts.This isn't the whole story however because the amplifier isn't biased at cutoff.The queiscent current is 125 ma. in the AL-811H and I'd assume its 3/4 of that in the AL-811.The tubes are producing 50-55 watts of heat each with no power output between characters on cw or between syllables on ssb.A zener diode of a few volts rating installed in the cathode circuit would dramatically reduce the "resting" current and its attendant heating.On cw that would be a good way to go but it might degrade the IMD performance of the amp on ssb and thus a switch might need to be provided to switch it out.

The claim of 800 watts pep output for the AL-811H (600 watts pep output for the AL-811) must have been dreamed up in the manufacturers sales/advertising dept.Reading the reviews on Eham.net,there are quite a few reports of actually measuring 650-700 watts pep output. These claims are mistaken and based on inaccurate peak reading wattmeters. The only reason an amplifier might put out higher power on ssb than cw is that momentary short duration voice peaks do not load the power supply quite as heavily and therefore the peak power output is higher on ssb. Don't expect it to be higher than perhaps 50-100 watts,if that.Using speech processing will narrow or eliminate even that edge.

Another factor that works to shorten the life of the 811A's in these amps is efficiency. Everyone likes to believe in and hope for 65-70% efficiency in their amp. Recently I had a couple of AL-811H's available to test. Both were within a few months of each other in date of manufacture and were around 6 or so years old.One was slightly used, the other unused. Both displayed quite similiar characteristics and I tested them using a Bird 43 wattmeter and a 1 KW slug (of known accuracy).I measured efficiencies as follows with 120 vac supply voltage:

160 m. - 51% (drive-50w) @520w output (pwr in-1026w)

80 m. - 57% (drive-40w) @570w output (pwr in-999w)

40 m. - 65% (drive-45w) @580w output (pwr in-885w)

30 m. - 33% (drive-22w) @200w output (pwr in-602w)

20 m. - 63% (drive-45w) @590w output (pwr in-934w)

17 m. - 56% (drive-40w) @520w output (pwr in-927w)

15 m. - 55% (drive-38w) @520w output (pwr in-940w)

12 m. - 54% (drive-38w) @500w output (pwr in-928w)

10 m. - 53% (drive-30w) @480w output (pwr in-897w)

In each case above, I stopped loading the amp when rated grid current of 125-130 ma. was reached. As you can see, the spread between input and output power is a low of 305w on 40 meters and a high of 506 on 160. The only reason you can get away with these powers being dissipated is because of the low duty cycle of cw and ssb and the "average heating' of the plates. On FM (above 29 MHz) and RTTY, both being 100% duty cycle modes, there is no tuning condition that can aleviate this as the plate power efficiency drops as you reduce the drive.It is recommended that power output be reduced for these modes to 300-400 watts depending on the source, brochure, ad, owners manual,etc. I would strongly discourage anyone from using one of these amps on these modes.They are not suitable for FM,RTTY,AM or any data mode.

If you must use these amps on 100% duty modes then 300-400 watts might be an acceptable figure for output if you substitute 572B's for the 811A's.I wouldn't consider any higher,even with a combined plate power dissipation rating of 640 watts because you'll likely overheat the power transformer. Personally, even then, I'd try to stick close to 300.

The sweep tube amplifier is no longer manufactured.Sweep tubes disappeared with the demise of the tube type television.These were tubes manufactured for high peak output/low duty cycle use as sweep oscillators.The sweep tube amplifier was relatively inexpensive with inexpensive tubes that were readily available and typically put out about 400 watts average.If one could master the idea that they were for light duty use and had to be tuned up quickly and allowed a generous cool down periodically,they worked well and lived up to their purpose admirably. The 811A amplifier is the modern day equivalent.One author of a "build it" article for a similiar amp in 1970 (Radio Handbook - William Orr W6SAI),recommended that tuneup should be for no longer than "15 second periods of time every 30 seconds".I'd recommend a shorter tuning and longer cooling interval of say, 10-12 seconds on and 45-50 seconds off.

There is little to no excuse for tuning on the air.Tuning should be performed into a 50 ohm dummy load.If necessary and you cannot provide your amplifier with a 50 ohm non reactive termination after tune up, use an antenna tuner of suitable power rating along with an antenna analyzer or noise bridge and find the tuning points on each band without causing qrm.Record those settings and return to a band without the necessity for tuning on the air.

As just one example, if a manufacturer designed a single 3-500Z amplifier to run at 2000 watts input you'd have an example of how the lowly 811A is treated in these amps.Perhaps the 3-500Z receives greater respect because it costs 2-3 times as much as four (4) 811A's.

If you care enough to learn what to do, you can improve the efficiency of your 811A amp. If not, then it would be wise to live within the limits of the tubes.A 1 db increase in output is the bare minimum that you must raise the power output of anything to make the smallest detectable change.That would involve raising the power out from 500 to 625 watts or
600 to 750. Even then, not everyone can perceive a 1 db change in power. As Alan rightly pointed out,a 3 db power change is probably the practical minimum worth pursuing.

Treat your 811A's with respect and don't believe everything written in the advertising department.

SUMMARY
-------
1)Don't overdrive them (22-50 watts, depending on band is typically the limit,no more)
2)Record the positions of the plate tuning and loading controls to allow for rapid return to a band
3)Key down tuning not to exceed 10-15 seconds with at least 15 seconds or more cool down; more is better.







 
RE: ALC, Keying, and Other Amplifier Problems  
by WA4DOU on February 7, 2007 Mail this to a friend!
I made a mistake above when I was transcribing the AL-811H info. There are 2 bands on which the amplifiers can be used on RTTY, and data modes - 40 and 20 meters. With less drive and tuning for maximum output, the efficiency is high and the difference between input and output remains below the plate power rating of the tubes, so 300-350 watts output under these conditions is possible. On the other bands the efficiency is too low to use RTTY or data modes.
 
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