I picked up a used AL-80B 1KW amp yesterday at the NEAR Fest.  It came with a not new extra tube.

I have it hooked up and throttled back to 800 watts with 65 watt input.  It will peak over 1100 watts at 100 watts input so I think it is working.

My question is this. I have never had an amp before and I now think I know how to tune it, but the ALC SET seems like the pot is scratchy, when adjusting the ALC the needle does not more smoothly with the pot, it jumps all over the place, I have to play with it to get the reading I want, so I would like to clean that pot or replace it. Any suggestions?

It is also an older AL-80B, so it does not have the ALC limiter pot on the back of the amp to limit the voltage to be compatible with the 0 to -4 V the IC-7300, so I have the ALC cable disconnected and am using just the internal ALC of the amp. I plan on adding a pot in the back to reduce the -10 volts the amp uses.

The Slugs on the back are tuned properly because the radio shows an SWR of unregistered while transmitting.

My question is, should I have an interface between the IC-7300 and the amp to protect the IC-7300 finals or is this not necessary?

How easy or hard would it be to clean that pot or replace it? Is it worth doing? Should I use the amp the way it is or not?

Thanks for any info.

If the amp has a tuned input, you should not need any impedance matching device between the radio and the amp.
Technically, you should not need ALC if you are careful not to overdrive the amp. Even if you do, it should not damage the radio but it may damage the tube. Watch grid current when transmitting and make sure to load it properly.
You can add a relatively inexpensive Grid Current Protection circuit to hopefully save the tube if anything goes wrong.
BTW, it's recommended to heat up the tube to dark red once in a while to remove any air infiltrated into the tube. Just leaving the heaters on will not do this on that partucular tube.  BTW, they are very robust tubes.

A drop of light machine oil (engine oil) into the potentiometer usually helps to remove oxidation from the resistive element and the slider. I've fixed a lot of potentiometers this way, if I could not take them apart for cleaning. If it's an open potentiometer and it's big enough to reach the element, a slight rub with a pensil eraser will clean the surface very well.
Beware that engine oil or many electrical cleaners may destroy some plastic parts.
You know, before you do anything, try moving the potentiometer back and forth a few dozen times. Sometimes this will clean the slider surfaces. If nothing else helps, you may need to replace it. Usually it's easy but will require some soldering.

Don't use engine oil. Spray it down with some trichloroethylene spray, then work the pot around good (do this with the power off, of course).

Said spray is available as common brake cleaner at auto parts stores, but make sure you read the ingredients and get the right stuff, don't get the non-chlorinated stuff.

thanks for the info

It might already have the grid current protection board, I will have to open it up and look before I order it.

I have tried just moving the pot knob a bunch but that has not worked

so I will try to clean it.

WD-40 is a very respectable contact cleaner - Commonly used for that purpose for many years.

I already have some of that.

I would not use that, or any type of lubricant, oil, kerosene, etc. It will leave a bunch of crap in your pot that you don't want there, and which will ultimately congeal into more problems as the amp gets a number of heat cycles on it. You want something that will completely evaporate. If you want to get all super professional, use this stuff:

http://www.crcindustries.com/products/qd-174-contact-cleaner-11-wt-oz-02130.html

or this stuff:

http://store.caig.com/s.nl/sc.2/category.188/.f

Some people actually use both as a step 1 and a step 2.

I've used machine oil numerous times back in my "home brewing" days.  It worked most of the time. Obviously it requires very little oil precisely delivered to the surface where the slider slides on the resistor. This is what we did to make it work when no replacements were available. Strong solvents found in many degreasers and cleaners may destroy a lot of plastic parts. I've seen some connectors fall apart within seconds of being sprayed with Electrical Cleaner. Be careful.
Nowadays it's so easy to get a replacement part. I would simply replace the potentiometer. Depending on the circuit, it may not need to be exactly the same value. If not sure get the same potentiometer.

BTW, AL-80 is a great amplifier. Do you know how old it is? Some old amps may eventually require new capacitors in the power supply.
Also, be careful if you need to get inside the amp. It takes some time to discharge high anode voltage caps after it's powered down. Usually there are some discharge resistors on the PS circuit for that purpose. It's a good practice to wait a few minutes and then shorten the anode to the casing briefly (with a screwdriver) to make sure the caps are completely discharged. This saved my ass once.

65 watts into the amp for 800 watts out, and 100 watts in for 1100 watts out is what I would
expect.  Good there.

An amp interface is not to protect the radio's finals.  

There is a phono cable from the transceiver to amp that when you press the mic's PTT button,
putting the transceiver in TX mode, the relay in the amp is tripped, putting the amp in TX, too.

Interfaces are sometimes used and meant to protect the output of the transceiver's keying circuit,
not the transceiver's finals.  Some amps' TX relays will draw enough current to toast the transistor
in the transceiver's keying circuit.

I have used an Icom IC-718, IC-7200, and Ten-Tec Jupiter with Ameritron AL-811H (very  similar
in operation to your AL-80) and Ameritron ALS-600S, all without interfaces, and without any problems.  
Other older amps may be a problem, but not your amp.  

If you really would feel better using an interface, don't buy anything... you can build this and simply
splice it into that phono cable from your Icom's "Send Control" jack to your amplifier's relay jack.  
And cover it all with some heat shrink tubing.  No box, no nuthin'.  And no expensive interface, just
$2 worth of parts, at most, or scrounged.

When you press PTT on your mic, the transceiver drops the center pin of that Phono jack to ground.  
This, in turn, grounds the TX relay in the amplifier, completing the circuit in the coil, switching the
amp to TX.

So, if you want to take the load off the switching transistor in the Icom, you can use that to trigger
a larger transistor.  Here's how... and you want to use the second circuit, the Positive voltage circuit:

Attached File


For negative voltage (top schematic) use:

NPN transistor, use Radio Shack 276-2017 (TIP-31) or 276-2020 (TIP-3055), MJE33.

For positive voltage (bottom schematic) use:

PNP transistor you may use Radio Shack 276-2027 (TIP42G).  May also use TIP-32, TIP-2955, MJE34.

1N4002 diode is Radio Shack 276-1102 or 276-1103.  May use 1N4003, 1N4004, etc.

1k 1/2w resistor is Radio Shack 271-1118.

Most amps, including Ameritron, are positive voltage PTT.

As for my Icoms and Ten-Tec, and Ameritron amps... "We don' need no stinkin' interface!"

amp is from 2003. power supply Caps were replaced 3 years ago according to owner.

The 12/10m mod is done

I get a solid 800 watts cw out of it on a steady tone which is the max rated for cw.



I have 3 concerns

1. the ALC pot, which should be easy to clean or replace

2. when I transmit SSB not when I key the mike but when the first word comes out of my mouth, the power jumps to 1100 watts then comes down to 800 while I talk. I dont know if that is normal but i dont think so. This is with 65 watts input. I dont think I am tuning it right for ssb. I csnt find a ssb 2 tone on my icom and me saying helllllow foes seem to work very well. Although I was getting a lot of unsolicited excellent audio reports. So I dont know.

3. the HV unloaded is 2800V which is low compared to the nominal 3100 in the manual but I have not checked my line voltage or the tap on the transformer. the valued stayed the same from the fest and my house. It is wired for 120 and it is not on a dedicated line. I failed to see what the loaded hv is. I need to do that

thanks for all the good info. I researched what the amp interface  was for last night and this morning ordered an ARB -704I2 at 0500 this morning from HRO before going to work.

Oh well.  $60. I looked at it as insurance but did not know. It will also do the ALC so there is that, although that looks like it is not needed for that either.

Also I used it for 8 hrs and was getting +15 db over 9 into Solvenia with S51DX but he has a massive yagi. I ussually get an S9 ftom him.

Switch to CW to tune it up....then switch to SSB

don't cry "HHHEEEEEELLLLOOOOO" like a damn CB'er

that is what I have been doing. Tuning in cw

Believe it or not that hhhhheeeeeeellllllloooooo thing is in the manual. lol

https://www.w8ji.com/loading_amplifier.htm

This might help the OP out.

The spike in RF output is most likely ALC overshoot from the IC-7300. This is a well documented issue with the radio.

No. Two of my teachers were TV repairmen on the side when I was taking electronics back in the dark ages and TV's had mechanical tuners. They told us WD40 was their best friend. When someone had their tuner start acting up and sprayed it with WD40, it would seem to fix it for a while, then the WD40 would dry out and make the tuner problem much worse so they had to take the TV in to be fixed. All they had to do was spray the tuner down with tuner cleaner and make a quick, easy repair charge.

great article thanks.

I am just beginning to understand how this stuff works, but maybe if I reduce the ALC voltage on the amp I may limit the grid current to an 800 watt value to surpress the amp power overshoot and prevent the 1100 watt spike to due the Icom ALC overshoot. It only happens in SSB not CW do I think it is likely ALC overshoot like you and that articke states. Nakes perfect sense. Also with thecamp buffer and using the Icom ALC connected to the amp, they nay or may not help.

I will also try reducing the mike gain to see if that has an effect. I currently have that at 75% which may be too high.

Thanks

also the instructions in the manual say to tune CW to max output increasing the load to the dip in power. I think that article is saying the same thing when it says tune to max power output then slightly more loaded so that any over shoots are better tolerated. Slightly more load would be just into the dip, but it does not nention a dip, just slightly less capacitance  from full power. Sounds like it is the same thing.

Which is exactly what I have been doing when tuning with a CW tone.

I do  not see the over shoot at full drive during CW tuning, I only see it in SSB at reduced input drive at 65 watts. I will have to go through this all again and write down the specifics to make sure I am not remembering it wrong.

I have to say it took me 8 months to find one of these amps at a good price. I joined the Lonley Guys net on Sat mornings 2 weeks ago and they were talking about NEAR Fest, which I knew nothing about. So I went and found this amp and the only seller that would power an amp up.

Very happy with it and got it for less than 50% of new which seems to be hard to do around here. The power supply caps being only 3 years old ( 14 year ild amp ) and the extra tube made it a deal I could not pass up, even though I know Eimac 3-500Z tubes sitting around do not gave a forever shelf life.

Don't sweat the "overshoot" issue. A lot of amps do that. The tube in the AL-80 is very tough. Technically you can use the amp without the ALC, especially if you already have the grid current protection board. For example, my Acom 1000 does not even have an ALC input and it works great. I've ran it at about 1300 watts in SSB mode with no issues.
Like mentioned by others, you don't need an interface for your radio. The interface is only required for very old amps that had high voltage PTT TX circuit and relatively high current to operate an internal relay.

For tuning, switch the radio to RTTY mode and slowly increase the output power in the radio.

Ameritron has some good videos on tuning the AL-811 and AL-811H amplifiers.  I don't if they
have a specific video for the AL-80B, but the principles are the same.  Look at your owner's
manual, and look at these.

https://www.youtube.com/watch?v=OT1UaCrVvd4

https://www.youtube.com/watch?v=zPcfRfn_No0

Over shoot from one of the early TS-590S rigs blew a cap in the 20M output network on my THP (solid state) amplifier. The US distributor was not happy fixing that under warranty repair.

never had any trouble with my TS-590 and SB-200 amp

....but when KenwoodUSA offered to upgrade/fix the overshoot problem, I sent it in and they did it free

Solid state amp is a totally different animal. It should have had several layers of protection anyway. Personally, I don't like solid state amps for many reasons.

BTW, I've seen amplifier components (often caps) damaged by "hot switching". Every decent HF rig should have a delay parameter in the menu to prevent this from happening. I usually set mine to about 15 ms.

My experience with audio gear, just replace it.  Once a pot gets noisy, it will always be noisy.  Cheap and
easy enough to replace.

Also, my Ten-Tec Jupiter lacks ALC amp control.  My amp works just fine without it.  I would prefer to
have it working, but it is really not a problem.

Well the Amp ALC is completely inop. It does not limit grid current like the manual says it does.

The amp still works there just is not any grid current limitation

to get 800 watts on a CW tone I need 170 ma of grid current. Seems kinda high.

I need to start writing these numbers down and make a chart. Seems like the tube might be a little soft. I expected that. I might try the other tube and see how that does.

What's your plate voltage? Lower than normal voltage may cause this. Proper tuning and loading is important as well.

BTW, like I mentioned in my previous post, have you changed the TX delay time in your 7300? It's set to zero by default, at the factory. Change it to at least 10 mS. It's in the menu. I had to change it in my 7300 when I bought it because I always use the amp at my base station.

I must have missed the part about Tx delay. I just changed it although I dont see any difference in anything

Is the plate voltage the same as the HV? HV is 2900 unloaded, which makes sense since my line voltage is 118.7 and the tap from the factory in the transformer is 125v. So the ratio from 3100 is the same

The instructions in the manual have been confusing,

I am starting to think that the amp does not have internal ALC and ALC only limits grid current when connected to the exciter for the feed back loop.

Is that true? If so then I have been trying to set something that will not set.

Well I cleaned the ALC pot and it now adjusts the ALC needle very smoothly. So that is fixed.

I hooked up the ALC to the IC-7300 and still can not get the ALC to limit Ig according to the directions in the manual.
Even with the ARB=704 interface I don't need but had already ordered.

on 20M here are the nums with a CW Tone

Plate is set at 8.5 and Load is 6.0 adjusted for max power output.

65w input   700w out     165ma Ig    400ma Ip

75w input   750w out      180ma Ig   425ma Ip

97w input    800w out      200ma Ig   475ma Ip

Do these numbers mean the tube is a little soft?Amp is rated at 800 watts out for CW

I get a max of 800w out with 65w in on SSB with an overshoot of 1100w on the first syllable of the transmission.

I am happy with 800 watts out on SSB. It has an RFparts tube.

Any comments about the ALC not working other than I don't need it.
Any ideas how to trouble shoot it?

Also do not have the Grid current protection board

I get a solid 1kw out with 73w input on 15 m

The way ALC works is it generates a negative going voltage that goes back to the radio. The more negative the voltage, the more the radio is supposed to cut back its RF power.

See also: http://www.eham.net/articles/10183 (just one a many such articles on the interweb).

What did you use to clean your ALC potentiometer?

OP,
Are you measuring the output power with a dummy load? If not, there will be some variations in output power on different bands. All amps do that. Where are you measuring the output power? What are you measuring it with?
I assume you have antenna tuner disabled in the radio right? If you switch the radio's meter to show SWR, does it show close to 1:1 with the amp active? The amplifier should have a tuned input. It's adjustable on many amps but I honestly don't remember if AL-80 has it adjustable easily. Also, sometimes changing coax length between radio and amp helps (based on practical experience).

I used locally available CRC QD Electronics Cleaner.

Safe for plastic, gets rid of gunk.

Fixed it after the first spray, then I cleaned it some more.

Measuring output with a 20m dipole inverted V. Very low SWR.

There are output variation on bands because I am using real antennas, but am only really working with 20m as a constant.

Measuring power out with the amp's internal power meter.

Antenna tuner in radio is off.

SWR on radio on all bands I have an antenna for 80/40/20/15 does not even register. All input slugs appear to be perfect.  Seller told me he tuned the 17/15 slug for 17 but I have been using in on 15 and get 1kw output with no measurable SWR on the radio with less than 100ma Ig on CW tone. I forget the input power being used for that. I was using it to talk to South America today on 15m.

Just use the thing and don't sweat it. No amp is perfect. Don't overdrive it and you'll be ok. The tube is very forgiving. IMHO of course.

Great choice

It's been a while since I worked on one of those. I did not read the whole service manual but it looks like the amp has a variable bias circuit (Q101, 102, 103). It turns off the bias when no or very low signal is present.
The external ALC output looks like a standard ALC that limits radio's output power. Obviously the ALC is dynamic and variable.
You'll have to measure idle current and bias voltage to verify it's operation. I honestly can't tell you how much power it should put out exactly. Based on what I remember and the fact that it uses the 3-500Z tube, 700 - 800 watts sounds about right, especially with the anode voltage not being near the max.

I am happy with the output.It's a used amp with a used tube, and it was less than 1/2 price of new.

The thing I would like to get to work is the ALC.

I follow the directions in the manual and it says it will lower the Ig by moving the ALC set pot counter clockwise and it starts off by limiting it to 100 ma Ig.

I turn the ALC pot, which now smoothly moves the ALC voltage set needle the way it should, but the Ig stays at 180ma instead of being limited at 100ma when the meter reading says it should be limited to 100ma.

I can not find anything on the web about this problem. I have read the manual directions and many other directions some linked here, and it just shows no sign of limiting Ig, so I have to assume either I am doing something drastically wrong or the ALC circuit is inop

Update: I fixed the ALC. It was a bad connection inside the amp on the center conductor of the ALC RCA connector. It looked fine until I poked it and it was loose. Resolder. Fixed.

Now the important issue.

If I key the amp with no RF input I get 30ma Ig and 75ma Ip.
This means that the bias circuit has failed. There should be no current on either the grid or the plate when keyed and no RF input. This accordin g to the trouble shooting guide by W8JI who designed the amp and the link posted by someone above. Thank you.

It also means the grid current needle follows the plate current needle and is not accurate, so I have no idea what the grid current is. I tested the D117 diode as suggested in the trouble shooting guide and it is shorted, just like the guide says. The Ip does not drop when loaded more than max power so I suspected something was wrong. Now I know. I have been using it at 600-800 watts anyway which should not cause any problems I hope. I just don't know what the currents are but since I am not pushing it, I hope it does not matter. I am tuning for max power and getting great unsolicited audio reports so I think I am tuning it right.

Ameritron tech support said that diode being shorted could make the Q3 on my old board (Q103 on the newer schematic) power transistor that turns on the tube also fail,and if that has failed the other 2 transistors in the circuit likely failed too. But the tube does turn on and the amp does hit almost full power on transmit, so I hope it is just the diode. And one I replace it the bias will hopefully work and the meters will hopefully be accurate.
Going to get one or a dozen of the diodes tomorrow and replace it.

This amp has lost the serial number sticker in the back. Seller said it was 14 years old. Except the main power board has a sep 4, 1994 date on it so the fucker lied and it is a 23 year old amp, not a 14 year old amp. The difference is inside with fault resistors not there like the newer ones and some 2 65volt MOV current clamping devices that I will try to add if I can find out where they go. W8JI suggests that be brought up to current production specs but does not go into detail on where they are. So I emailed him. Hopefully he has the time to answer with some info. I have learned alot about the amp but there is so much I don't know. I just hope the only thing blown is the diode.

I paid less than 1/2 new for this amp, guy said nothing was wrong with it,  except there is. So there is that. Still less than 1/2 price of new so I guess I don't have much to complain about. Maybe I will get it fixed for the contest tomorrow, but I doubt it.

Most annoying! But it sounds like you are a diode away from a 100% functional amp, so don't lose hope! On the plus side, since you've had to fuss with it so much, you are now much better prepared to maintain it in the future

If I remember correctly, some AL-80 owners have disabled the automatic bias control feature. They claimed that it's not quick enough or good enough. It made some weird noise in their audio.


Edited: Found an article about it: Link

I did see that and W8JI dedigned the radio and has posted online that was a problem with the early amps and I have an early amp because of how he took the RF to turn in the bias circuit. It was fixed in later models of the amp. I will see what kind of audio reports I get now that I just replaced components in the bias circuit.

Still, I had a bias circuit failure and the Ig and Ip readings were completely innacurate. I found a blown diode and blown Q103 power transistor and just finished replacing them and it now works the way it should right down to the letter.  

So I am happy I was able to get the parts at the local parts store. glad I remembered heat transfer paste for the power transitor and happy Ivwas able to fix it.

Yay!

And I would be willing to bet that what you did exceeds 99% of most ham capabilities. Researched the problem, interpreted schematics, debugged the board, ordered the right parts, reworked the board, and successfully.

Most hams can't even figure out how to build a microphone cable.

One of my faults is that I have always been the type to do it myself and enjoy fixing stuff.

And I don't have time for everything, so things don't get done.

The only thing that concerned me was the HV. I have been shocked across the chest before and it sucked, both times.

3KV would be the last time for sure.

In full disclosure I have a BS in Electrical Engineering and I have a basic understanding of electrical stuff, even though most of those brain cells appear to be inop from decades of decay and drinking.

I am very happy I was able to fix it but pissed I was sold a broken amp that was stated to be fully working.