AL-80A question, help please - Amplifiers Forum at eHam.net

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eHam.net Forum : Amplifiers : AL-80A question, help please

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AL-80A question, help please	Reply
by WD259 on October 23, 2009	Mail this to a friend!
Hello All, Trying to help out a friend with his concerns with his older AL-80A Ameritron amp. I'm pretty familiar with the 811 and other amp series, but learning on the this one so I thought I would ask the experts. The amp runs pretty good on the lower bands (20/40) at about 700-800 watts. Setup is normal per the book 3100 volts @ 50-100ma with no exciter. Tunes up no issues, plate knob in the proper area for the bands. On 75 and 160, the plate knob locates between 20 and 40 meters on the plate band scale and only about 400-500 watts max output. We are wondering if there is a failing component in the plate tuning network or where to start looking for the cause. The tube is pretty old, but seems to be pretty stout on the other bands. Any words or wisdom or suggestions on where to go from here? I have a good amount of test gear; LC meter, scope etc, just need some guidance. Thanks for the help. 73 DE Dave KD8GEH

RE: AL-80A question, help please	Reply
by K4RVN on October 23, 2009	Mail this to a friend!
The tuned input circuit may need to be adjusted. My AL 80A did the same thing for years until a few months ago. There are slug tuned coils that can be adjusted behind the band switch under the cover. Your problem may be that the exciter is not providing enough power to drive the amp for its rated output due to the tuned input being out of adjustment. I had that problem and could only get 450 to 600 watts max out. Since the adjustment, I can get full output on most bands with 90 watts drive on my transceiver. I used a dummy load to adjust mine, took about 30 minutes from start to finish. This assumes that your 3-500Z is OK. I bought a new one which did not fix the output problem, then got serious and did some thinking. It's running great now on all bands. If you don't feel good about the adjustment yourself, get a tech to do it. I only used 5 watts drive during the adjustment to peak each slug. Be careful of the HV, and only slide the cover back enough to get your tool into the coil holes. Call Ameritron to determine which hole is for each band or email me and I'll dig out the info they sent me after I called. Good luck.

RE: AL-80A question, help please	Reply
by K6AER on October 23, 2009	Mail this to a friend!
I don’t know if the A model is much different than the B model but I’ll bet the tank circuit is about the same. Maybe Tom, W8JI could jump in here. Make sure the padder capacitors on the tank band switch, C15-170 pF, C16-500 pF and C17-170 pF are not burned and the switch contacts are good. Many hams forget to move the band switch from 80-160 at night to 20 in the morning and load up the amplifier with a 20 meter signal with the band switch in the 80-160 meter position. The amplifier loads very nicely until the switch contacts let go or the capacitors burn up.

RE: AL-80A question, help please	Reply
by W8JI on October 24, 2009	Mail this to a friend!
What is the input SWR indicated on the radio's SWR meter when the amp is running on 160 Dave?? Are you using the radio's tuner? If so shut it off. What radio do you have? How much power does it make into the amp on 160? What power indicating meter do you have? How much grid current do you have on 160? How much plate current do you have on 160? Without knowing all of these things, it is all a guessing game. Tom

RE: AL-80A question, help please	Reply
by WD259 on October 25, 2009	Mail this to a friend!
Thanks all for the info. I'll pop the cover off, take a look around and do some readings. Let you know what I come up with. 73 DE Dave KD8GEH

RE: AL-80A question, help please	Reply
by W8JI on October 26, 2009	Mail this to a friend!
Dave, I designed that amplifier. I even managed the company. You can tell everything you need to know from OUTSIDE the cabinet. You do not need to "pop the cover off and take readings". That is not good for the amplifier and it can get you killed. I'm afraid in the haste to give answers it is very common on eHam to not ask the right questions. The only way anyone could really tell you what is wrong is if they know answers to all the questions I asked, ALL of which can be answered without removing the cover. Slow and steady will win the race, poking around inside on a wild guess can get you killed. Tom

RE: AL-80A question, help please	Reply
by WD259 on October 26, 2009	Mail this to a friend!
Hi Tom, Thanks for the heads up and the concern. My intention was to look for bad caps/components and replace a pilot then run it up with the cover on. Pretty familiar with HV, not planning on even changing a meter lamp without bleeding the caps off. I can just get the current measurements for now. I do have some data , although second hand and will confirm: Are you using the radio's tuner? If so shut it off. No direct into res di-pole What radio do you have? How much power does it make into the amp on 160? Icom IC-7000 80-85 watts What power indicating meter do you have? He has the amp meter and the watt meter in the Palstar tuner only How much grid current do you have on 160? He says 150mA How much plate current do you have on 160? Unknown Thanks again all for the concern and help, esp you Tom. You have a wonderful rep and do fine design work. Keep you informed. Dave KD8GEH

RE: AL-80A question, help please	Reply
by WB2WIK on October 26, 2009	Mail this to a friend!
.RE: AL-80A question, help please Reply by WD259 on October 26, 2009 Mail this to a friend! Are you using the radio's tuner? If so shut it off. No direct into res di-pole< ::That wasn't Tom's question. The question was, do you have a tuner in the radio itself? This has nothing to do with your antenna. It's a simple question, either yes, or no, and pertains only to the RADIO. >What power indicating meter do you have? He has the amp meter and the watt meter in the Palstar tuner only How much grid current do you have on 160? He says 150mA How much plate current do you have on 160? Unknown< ::How can this be "unknown?" The plate current is read by the same meter as the grid current, just using the other needle and scale. Are you saying the plate current meter doesn't work?? WB2WIK/6

RE: AL-80A question, help please	Reply
by W8JI on October 26, 2009	Mail this to a friend!
It is unlikely you have a bad component you will see. Let's see what the 160 meter input SWR to the amp is (indicted on the radio) when the amp is operating, and what plate current is at that grid current. Use FM or RTTY or CW carrier.

RE: AL-80A question, help please	Reply
by WD259 on October 26, 2009	Mail this to a friend!
Thanks again Tom, and for your comment Steve. As noted before I dont have the amp in my shack yet. He's going to bring it over this week and we'll see what we get. Sorry if I wasn't clear, tuner off in the radio on the question. Take care, Dave

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