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[Articles Home]  [Add Article]  

ALC, Keying, and Other Amplifier Problems

from Alan Applegate, K0BG on May 2, 2014
View comments about this article!

"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the eHam.net team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 1/26/2007





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 W1JKA on May 2, 2014 Mail this to a friend!
For me this is a most timely, interesting and informative article even though within my niche of the hobby an amplifier is not needed or even desired. When I occasionally listen in on the voice sections of the bands I now have a better understanding of the cause of many poor signals and wasted bandwidth of some high end high power station operators. I hope a few of them read this article, take heed and at least make an attempt to re educate themselves in this area.
 
ALC, Keying, and Other Amplifier Problems  
by WD8OOJ on May 2, 2014 Mail this to a friend!
Fantasic Artical to read entirely ..
 
RE: ALC, Keying, and Other Amplifier Problems  
by K9MHZ on May 2, 2014 Mail this to a friend!
"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."


This drove me nuts when I first opened up my Dentron MLA-2500 back in the 80s. No internet to download schematics, product reviews, etc. Just a very lame swamping resistor at the input. I learned a very valuable lesson in researching before buying. What a ridiculous joke of an amplifier.

Anyway yes, a really nice article. Moderators....thanks for reposting it!
 
RE: ALC, Keying, and Other Amplifier Problems  
by K4PIH on May 2, 2014 Mail this to a friend!
I'm going to print this and keep it in my shack handbook. Everyone should have a shack handbook to keep articles, information and notes in a common place. I run a piece of legacy equiopment from time to time and the information in this article is valuable. It's also good to hear that someone else thinks the same way about power and the inner CB skip shooter in all of us. It's also what the forum is designed to be, not a whine list.

Thanks!

73
 
ALC, Keying, and Other Amplifier Problems  
by K6YE on May 2, 2014 Mail this to a friend!
Alan,

Another splendid article from the past. 4CX800s are getting long in tooth and I plan to get something using an 8877.

Semper Fi,

Tommy - K6YE
DX IS and CW RULES
 
ALC, Keying, and Other Amplifier Problems  
by K6YE on May 2, 2014 Mail this to a friend!
Alan,

Another splendid article from the past. 4CX800s are getting long in tooth and I plan to get something using an 8877.

Semper Fi,

Tommy - K6YE
DX IS and CW RULES
 
ALC, Keying, and Other Amplifier Problems  
by K6YE on May 2, 2014 Mail this to a friend!
Alan,

Another splendid article from the past. 4CX800s are getting long in tooth and I plan to get something using an 8877.

Semper Fi,

Tommy - K6YE
DX IS and CW RULES
 
RE: ALC, Keying, and Other Amplifier Problems  
by K6AER on May 2, 2014 Mail this to a friend!
Excellent article Alan.

I might add in today’s newer transceivers the internal ALC is all that is needed with the addition of an amplifier. Back in the tube days, transceivers had no ALC to speak of and the feedback network from the amplifier ALC output to the transceiver was necessary to keep from overdriving the amplifier. We are talking FT-101E here.

With newer radios, post 1997, just set up the amplifier so the maximum transceiver output drive keeps the amplifier out of compression. Done, nothing more needs to be added. The ALC in the transceiver will keep the amplifier from being overdriven. A number of amplifier manufactures including Alpha do not provide ALC outputs on their amplifiers any more.

Keying as Alan mentioned can be a problem with old amps and newer radios with transistor keying. Personally I just use a simple 12 volt reed relay from Radio Shack and keying polarity is not a problem.

In reference to Steve Kats (WB2WIK) “all knobs to the right” is true. This mentality is responsible for most of the splatter heard on the band.
 
ALC, Keying, and Other Amplifier Problems  
by W5TTW on May 2, 2014 Mail this to a friend!
Nice read. (I sincerely hope that the comments section will not include the usual mindless political diatribe of the no-call sign contingent.)
 
ALC, Keying, and Other Amplifier Problems  
by W5TTW on May 2, 2014 Mail this to a friend!
Nice read. (I sincerely hope that the comments section will not include the usual mindless political diatribe of the no-call sign contingent.)
 
RE: ALC, Keying, and Other Amplifier Problems  
by M6GOM on May 2, 2014 Mail this to a friend!
All the hassle of amps is why I've never bothered with one. The 400W limit in the UK makes it not worth bothering over running barefoot.

The point about the TX audio was spot on. Last night I was listening to an IZ0, or at least I assume it was, trying to make contact with a JA. Even though the IZ0 was S9 to me his audio was so overdriven and distorted I couldn't make out what his callsign was. The JA stood no chance. Eventually I got sick of waiting, put my call out and got through straight away first time with just 100W. Knowing the Italians that was probably less than 1/10th of the power he was using.

I have a rule when setting up my TX levels for SSB: If there's more than a tickle of ALC showing on peaks its too high. As a result I run mic gain and Proc IN/OUT levels that many would consider very low. I've never had anyone tell me I sound too quiet and I put out max power on peaks. What I have experienced is breaking through lots of pile ups usually in the first call or two despite only running barefoot.

Turn down the mic gain, you may just find things improve.
 
RE: ALC, Keying, and Other Amplifier Problems  
by M6GOM on May 2, 2014 Mail this to a friend!
All the hassle of amps is why I've never bothered with one. The 400W limit in the UK makes it not worth bothering over running barefoot.

The point about the TX audio was spot on. Last night I was listening to an IZ0, or at least I assume it was, trying to make contact with a JA. Even though the IZ0 was S9 to me his audio was so overdriven and distorted I couldn't make out what his callsign was. The JA stood no chance. Eventually I got sick of waiting, put my call out and got through straight away first time with just 100W. Knowing the Italians that was probably less than 1/10th of the power he was using.

I have a rule when setting up my TX levels for SSB: If there's more than a tickle of ALC showing on peaks its too high. As a result I run mic gain and Proc IN/OUT levels that many would consider very low. I've never had anyone tell me I sound too quiet and I put out max power on peaks. What I have experienced is breaking through lots of pile ups usually in the first call or two despite only running barefoot.

Turn down the mic gain, you may just find things improve.
 
ALC, Keying, and Other Amplifier Problems  
by ZENKI on May 2, 2014 Mail this to a friend!
After reading all the good advice and putting it into practice, the best solution is to monitor your signal.

With the widespread availability of SDR receivers, every ham station today should own a SDR receiver for signal monitoring purposes.

SDR receiver dont lies like "ham buddies" who are afraid to be real friends and tell other hams the truth about another stations signal quality even if it means telling lies.

A SDR receiver makes an excellent diagnostic tool and can spot all faults related to transmission quality like ALC incompatibility, ALC compressions, splatter and things like transceiver and amplifier relay timing issues.

The bottom line is that the typical good SDR receiver performs better than standard sweeping spectrum analyzers that costs many times more and which has insufficient speed and dynamic range to spot transmitter issues.

Every ham should have a SDR receiver monitoring their output of either their radio or amplifier. As the saying goes a picture is worth 1000 words, and SDR receivers offline and online are capturing ham radios dirty little secrets that manufacturers and amplifier manufacturers dont want you to talk about.

 
ALC, Keying, and Other Amplifier Problems  
by ZENKI on May 2, 2014 Mail this to a friend!
After reading all the good advice and putting it into practice, the best solution is to monitor your signal.

With the widespread availability of SDR receivers, every ham station today should own a SDR receiver for signal monitoring purposes.

SDR receiver dont lies like "ham buddies" who are afraid to be real friends and tell other hams the truth about another stations signal quality even if it means telling lies.

A SDR receiver makes an excellent diagnostic tool and can spot all faults related to transmission quality like ALC incompatibility, ALC compressions, splatter and things like transceiver and amplifier relay timing issues.

The bottom line is that the typical good SDR receiver performs better than standard sweeping spectrum analyzers that costs many times more and which has insufficient speed and dynamic range to spot transmitter issues.

Every ham should have a SDR receiver monitoring their output of either their radio or amplifier. As the saying goes a picture is worth 1000 words, and SDR receivers offline and online are capturing ham radios dirty little secrets that manufacturers and amplifier manufacturers dont want you to talk about.

 
ALC, Keying, and Other Amplifier Problems  
by ZENKI on May 2, 2014 Mail this to a friend!
After reading all the good advice and putting it into practice, the best solution is to monitor your signal.

With the widespread availability of SDR receivers, every ham station today should own a SDR receiver for signal monitoring purposes.

SDR receiver dont lies like "ham buddies" who are afraid to be real friends and tell other hams the truth about another stations signal quality even if it means telling lies.

A SDR receiver makes an excellent diagnostic tool and can spot all faults related to transmission quality like ALC incompatibility, ALC compressions, splatter and things like transceiver and amplifier relay timing issues.

The bottom line is that the typical good SDR receiver performs better than standard sweeping spectrum analyzers that costs many times more and which has insufficient speed and dynamic range to spot transmitter issues.

Every ham should have a SDR receiver monitoring their output of either their radio or amplifier. As the saying goes a picture is worth 1000 words, and SDR receivers offline and online are capturing ham radios dirty little secrets that manufacturers and amplifier manufacturers dont want you to talk about.
 
ALC, Keying, and Other Amplifier Problems  
by JOHNZ on May 2, 2014 Mail this to a friend!
Very nice technical piece, well written and organized!

IMD is something very few hams pay attention to. Toward that end, the Agilent E 5072 A ENA series network analyzer is an excellent tool, but granted, probably beyond the reach of the average ham radio operator.

In radio systems, we should be concerned with spurii within the IF passband, such as the 3rd order intermodulation products, 2f sub 1 minus f sub 2 and 2f sub 2 minus f sub 1.

The more more CB power mentality goes hand-in-hand with the guy who shouts into the mic, so the other station can hear him better or the guy who puts out on the DX cluster that the DX station is "very loud." Loud where? Do you mean the DX station has a great signal at YOUR QTH?
 
RE: ALC, Keying, and Other Amplifier Problems  
by K3ZL on May 2, 2014 Mail this to a friend!
After 60 years of hamming I can say that I never found it necessary to use an amplifier. The most power I have ever used was 125 watts out. That has been adequate to QSO stations all over the world with no problem. To me, running a "full gallon" is wasteful in bandwidth and power consumption as well being just plain unnecessary. I would like the League to petition the the FCC to limit total output to something like let's say, 400 Watts. Just one man's opinion, as unpopular as it may be. It's still the Land Of The Free. Cheers!
 
ALC, Keying, and Other Amplifier Problems  
by ZENKI on May 2, 2014 Mail this to a friend!
After reading all the good advice and putting it into practice, the best solution is to monitor your signal.

With the widespread availability of SDR receivers, every ham station today should own a SDR receiver for signal monitoring purposes.

SDR receiver dont lies like "ham buddies" who are afraid to be real friends and tell other hams the truth about another stations signal quality even if it means telling lies.

A SDR receiver makes an excellent diagnostic tool and can spot all faults related to transmission quality like ALC incompatibility, ALC compressions, splatter and things like transceiver and amplifier relay timing issues.

The bottom line is that the typical good SDR receiver performs better than standard sweeping spectrum analyzers that costs many times more and which has insufficient speed and dynamic range to spot transmitter issues.

Every ham should have a SDR receiver monitoring their output of either their radio or amplifier. As the saying goes a picture is worth 1000 words, and SDR receivers offline and online are capturing ham radios dirty little secrets that manufacturers and amplifier manufacturers dont want you to talk about.
 
RE: ALC, Keying, and Other Amplifier Problems  
by KM3F on May 2, 2014 Mail this to a friend!
Excellent as always, but the variables in equipment makes all this difficult for the non technical.
For many of the rest, it scares them to try it.
I have spent a lot of time on setup testing and procedure with an amplifier, ALC feedback, Mike and Processor setup and tuner adjustment.
The amplifier is a given more or less for tuning on each band.
The Tuner is an old Heathkit SA2060 with Cin and Cout set to mid scale and only the roller L changed on each band. Make tuning much faster.
Latest procedure involves an older Autek WM-1 peak reading Power/SWR meter that is well thought of for good accuracy and performance.
For tuning I use the transceiver internal dot keyer set to just enough speed to stabilize the peak reading meter on the output of the amplifier.
Lets not confuse the internal keyer operation with that of a 'pecker' circuit as it not the same even though it may sound the same on the air but cleaner.
The internal keyer does the same thing as done in using the radio on CW with a paddle key,
with or without an amplifier online.
Once the rough settings have been made on the amplifier and the tuner, before transmitting, it is only a matter of driving the system with the internal keyer operated from an external switch, to peak the settings on the amplifier and the tuner using no more than several 5 second bursts of Dot strings as shown on the Autek peak reading meter.
This certainly should not cause big QRM from long time tuning that I hear going on all the time..
This is done with no ALC dialed in.
After peaking, the ALC is dialed in to reduce the AL80B grid current to 50 ma +/- while showing the power out a near a full Kw on the Dot string.
The transceiver is run near full on at about 95 watts setting or just at the point the peak begins to drop with Manuel power cut back on Dot string drive, letting the ALC take full charge of the system dynamics when ALC is dialed in.
It's pretty nice seeing a full KW with 50 ma of average grid current near rock steady while in a SSB contact.
The 3-500 tube in the amplifier is now 5 years old from the time I got the unit used and beat down from RTTY use.
.
Processor adjustment:
Read you manual on how to initially set it up first.
Set up with the mike you will most use.
Back ground:
Many think a processor should make the received audio practically break the speaker cone on the other end. Not so. If you already give another station an S7 or better, turning on Processor will make little difference. This is normal because your signal level already has the receiver AGC shut down. There is very little more in signal level to be achieved, however if one looks at the Average power out of the transmitter it will show to be higher.
Processors only to be used when your signal level is marginal to the other station in contact.
This is when Processing makes a difference, properly set up and causes no audio distortion.
Note on some makes and models the frequency response is automically changed to cut off/reduce the low end audio when processing is turned on. This is to further enhance the use of processing when it is really counts.
.
Lastly, ALC feed back does a bit of processing the same thing, in a different way. By causing a gentle handling of RF compression, the average signal level does increase and all this without over driving the amplifier and causing splatter, if done correctly.
A station next to you, if close in pass band may experience QRM (in his opinion) from just high signal strength but, that's life on the bands.
As to the question of needing to run an amplifier, that's left to the individuals point of view.
There are people who try to run 5 watts on a noisy band and can't be copied well enough to be of any value, but they keep doing it for the wow factor, I guess..
I have yet to be told of splatter from my station occurring up and down the band to warrant a review of the procedure.
I'm sure someone will find disagreement but that's why were here to talk about it and maybe learn.
Good luck.
 
RE: ALC, Keying, and Other Amplifier Problems  
by BOYSCLUBRADIO on May 2, 2014 Mail this to a friend!
Alan you mention spare tubes... I have been told that after a while even those go bad just sitting in the box. How long WILL a tube be good for before placed into service ?

I have seen articles on how to burn 'em in... but, most seem to leave short exactly how long a tube is good for... in storage... such as the 572, 3-500...
 
ALC, Keying, and Other Amplifier Problems  
by K3SSB on May 3, 2014 Mail this to a friend!
Wonderful article. Useful and concise information that should be retained and re-read periodically.

However, there is nothing to match the glow of a glass envelope tube on a frigid winter day.

A memory stirs...

"I'll give you my tube RF amplifier when you pry (or take) it from my cold, dead hands"

tnx es 73

K3SSB
 
RE: ALC, Keying, and Other Amplifier Problems  
by K6AER on May 3, 2014 Mail this to a friend!
Glass tubes will suffer oxygen migration past the tube pins over a period from a few years to 10 years. To prevent this you must run the tube until the anode gets bright. This activated the gettering(zirconium)on the anode which eats up the oxygen molecules.

The best thing to do with glass tube finals is to run them at specification every few years. Most hams have spare sets and rotate them every year. The worst thing can do to tube finals is not run them at rated output

Ceramic tubes do not have this problem.
 
RE: ALC, Keying, and Other Amplifier Problems  
by K9MHZ on May 4, 2014 Mail this to a friend!
AER....

Interesting, thanks!
 
RE: ALC, Keying, and Other Amplifier Problems  
by W4KVW on May 4, 2014 Mail this to a friend!
Tuning an Amplifier?Let's see,turn on the amp,choose the band & frequency,key the foot switch & contact made.Love my ICOM PW-1 & YES I do have the ALC connected & Properly adjusted,Automatic tuning is the ticket & WELL worth the price of the feature! {:>)

Clayton
W4KVW
 
ALC, Keying, and Other Amplifier Problems  
by W5JO on May 5, 2014 Mail this to a friend!
When dealing with ALC I suggest you do not hook the amplifier to the transceiver or other exciter. This can be a source of problems that cause splatter and it is evident on the bands. Simply excite your transceiver with the proper amount of audio by using the ALC scale on your transceiver. And, no, it does not have to stay on the top of the scale with every syllable.

There is a small delay between when the amp develops the ALC voltage and when it arrives at your audio circuit which can cause the audio to very briefly overdrive the amp tubes. Use your audio gain control to set the ALC on your transceiver to average about the middle of the scale or recommended value and problems won't occur.
 
RE: ALC, Keying, and Other Amplifier Problems  
by W5JO on May 5, 2014 Mail this to a friend!
I have installed tubes that were over 20 years old that were never used or had the filament lit without problems. Wonder why?

This is a bit of myth that started on the CB bands. Seepage around the tube pins occur because people rock them to remove then from the socket causing minor stress cracks that enlarge as the tube heats and cools. By changing them from time to time, you risk breaking that seal.
 
RE: ALC, Keying, and Other Amplifier Problems  
by K9MHZ on May 5, 2014 Mail this to a friend!
I think a lot of sweep tube amps especially (CB, and junkier ham amps like the GLA-1000) would develop a bit of resistance on the tube pins in their sockets, so "rocking them" would break up a bit of that micro-corrosion and yes, the operator would see some improved performance. "More wattage" as CBers and some hams would say. "Roger?"
 
ALC, Keying, and Other Amplifier Problems  
by RSHIRE22 on May 5, 2014 Mail this to a friend!
Sinko de Myo is derived from the Mexican-American War. The Mexicans had a ship named de Mayo and we sunk it.


RS
 
ALC, Keying, and Other Amplifier Problems  
by RSHIRE22 on May 5, 2014 Mail this to a friend!
Liberals, don't be so sensitive - one of your biggest problems!
 
RE: ALC, Keying, and Other Amplifier Problems  
by N4OI on May 6, 2014 Mail this to a friend!
Kind of surprising the "hot switch" issue was not mentioned in the Relay section. Some vintage transceivers can even delay the relay switchover until after RF is present. When that happens, be prepared to get a little more familiar with the internals of your amp! From now on, I for one will always confirm the relay/RF timing with a scope before interfacing any new transceiver.

73
 
ALC, Keying, and Other Amplifier Problems  
by WA7PRC on May 17, 2014 Mail this to a friend!
A good article, Alan. A few decades ago, approximately 20 years before the internet existed, a SB-610 monitor 'scope showed me I was seriously underloading (and flat-topping & splattering with) my Heath SB-220. I now use a lab 'scope (Tek 2236) with a larger CRT + triggered sweep as a monitor.

An oscilloscope won't show you how wide you are but, if you're not flat-topping, it's a good bet that you're not splattering. Only a Spectrum Analyzer will tell you for certain whether or not your signal is wider than it should be. However, most SAs are not cheap, and require setup that isn't fast. A lab scope with enough bandwidth (at least twice the radio frequency) should cost around $1/MHz, give or take a bit.

Today, with modern rigs, I do not use my amplifier's ALC output. Instead, I use an outboard audio box (the discontinued Symetrix 528E) that includes a limiter/compressor. Running enough depth, the output is pretty constant, and without ALC under/overshoot and time constant problems. That's how we did it in broadcast engineering. I see that MFJ sells a similar box, the MFJ-655B.

The issue of T/R control interfacing for legacy amplifiers to modern xcvrs can be a matter of instantaneous switching current. For example, when transitioning from RX to TX, the 0.02uF across the ANT RELAY jack of the Heath SB-220 pushes a short 6A pulse of current thru the transceiver's amplifier control device. If the device is a transistor, it will eventually result in a shorted transistor. If the device is an itty-bitty relay, the contacts will eventually weld themselves closed. The simplest fix (as long as the xcvr can handle the open-circuit voltage) is a small resistance in series to limit the current pulse. Jim W7RY offers relay driver PCB kits that include electronic bias regulation + switching. Jim can supply the input reed relay and he points the user to a source for the output vacuum relay. You wind-up with a FAST and QUIET amplifier T/R system that any xcvr can drive.

vy 73,
Bryan WA7PRC
 
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