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Author Topic: what did i do wrong?  (Read 34826 times)
AE7IS
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Posts: 96




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« on: November 13, 2014, 08:50:00 PM »

hooked up the 811 to the 590.  yes i read the manual (both)  wired correctly, antenna less than 1.5/1, set the plate and loading as the manual indicated.  disconnected the alc, kept exciter power level at 65 watts (per meter on 590)one meter reads right on, but grid meter doesn't.  It shows 45-50 where it should be 100-150 (manual)  didn't matter if I was using cw or usb, tried from 20-10 meters, no real difference.  the only way I can get the grid meter to come close is to overload the plate voltage (just for a second)  alc plugged in , no difference.   so please, where do i look first?
I appreciate any help or guidance.
mahalo and thanks
frank
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NO2A
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Posts: 1400




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« Reply #1 on: November 13, 2014, 11:09:29 PM »

If you`re not sure how to properly tune the amp stop before you do any damage. When you first apply drive do it with low power,say 5-10 watts then peak the plate cap for max output. Is your swr on the `590 low enough? If grid current is too low the rig may be seeing too high an swr to deliver full output to drive the amp.
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KH6AQ
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Posts: 7987




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« Reply #2 on: November 14, 2014, 04:47:02 AM »

I would not worry about the grid current unless it hits the specified limit. Adjust TUNE and LOAD for maximum RF output (to tune this amp you must have an RF power meter) while keeping the RF drive such that the RF output does not exceed 600 watts.
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W8JX
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Posts: 13268




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« Reply #3 on: November 14, 2014, 04:55:47 AM »

I would not worry about the grid current unless it hits the specified limit. Adjust TUNE and LOAD for maximum RF output (to tune this amp you must have an RF power meter) while keeping the RF drive such that the RF output does not exceed 600 watts.

600 watts is playing with fire as you have to exceed tube ratings to get there. 450 to 500 tops if you want reasonable tube life.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KH6AQ
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Posts: 7987




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« Reply #4 on: November 14, 2014, 05:54:35 AM »

Running 600 watts of CW (50% duty cycle) with 65% efficiency causes the tubes to dissipate 54 watts. That is below the 65 watt ICAS rating. I always liked the dull red plate color when running CW on my AL-811.
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W8JX
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Posts: 13268




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« Reply #5 on: November 14, 2014, 06:16:55 AM »

Running 600 watts of CW (50% duty cycle) with 65% efficiency causes the tubes to dissipate 54 watts. That is below the 65 watt ICAS rating. I always liked the dull red plate color when running CW on my AL-811.

Great math but not accurate. During key down you will be dissipating at least 100 watts per tube which is over twice the rated continuous dissipation. Also zero signal plate current is running about 40 watts so tubes are really loaded even then. When you look at a old SB 200 at 600 out even with just 2 tubes you are below tubes ratings. Many many operator have melted/damaged tubes in AL811 amp trying to run rated power. I consider it bad advice to recommend running 3 tube amp at 600 watts.   
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Ham since 1969....  Old School 20wpm REAL Extra Class..
AE7IS
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Posts: 96




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« Reply #6 on: November 14, 2014, 07:08:34 AM »

thanks for the input.  I really wasn't trying to run 600 watts, simply following the manual.  I did start with 10 watts exciter input , going up to 60-70 .  when I first started the grid meter didn't even move that was on 20 meters.  when i went to 15 meters and retuned for that band then i got movement.  but no matter what it stayed around 45 on the meter.  the antenna is a hex beam, swr running barefoot hasn't gone above 1.3-1 on any band.  just adding an amp wouldn't change that right?  Yes this is my first time trying to tune an amp.  If one doesn't follow the manual then how should I be doing it?  in other words, how do you learn unless you jump in?  like I said, the grid meter is the only one showing abnormal movement.

what would cause this?  this is a used 811, looking on the net , I got that the tubes may be weak but that seems to be the only thing i could find.  keep 'em coming please.  its obvious i need help.  thanks
frank
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W8JX
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Posts: 13268




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« Reply #7 on: November 14, 2014, 07:17:39 AM »

Low grid current tends to suggest low drive or soft tubes or a high input SWR to amp that will fold drive power back even if it is set to a higher level. Try this, engage auto tuner on rig and hit tune with amp on line and see if that changes things. If it does, you have a problem with amp input tuning.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
AE7IS
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Posts: 96




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« Reply #8 on: November 14, 2014, 08:06:56 AM »

should i get a watt meter?  or anything else ?  I really don't want to cause a problem with the amp or the radio.
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KB4QAA
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Posts: 3342




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« Reply #9 on: November 14, 2014, 08:51:01 AM »

Yes, you should have a watt meter. 

A watt meter can't harm anything.  How could it?
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KA0HCP, ex-KB4QAA Relocated to Ks. April 2019.
W8JX
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Posts: 13268




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« Reply #10 on: November 14, 2014, 08:53:23 AM »

should i get a watt meter?  or anything else ?  I really don't want to cause a problem with the amp or the radio.

Engaging auto tuner on rig will not damage anything. If drive/grid current increases then it shows there is a mismatch in amp input.

A watt meter is not a "got to have" but it is nice.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WB2WIK
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Posts: 21837




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« Reply #11 on: November 14, 2014, 10:48:07 AM »

should i get a watt meter?  or anything else ?  I really don't want to cause a problem with the amp or the radio.

How are you tuning up the amp without a wattmeter or some sort of power output indication?

The AL-811 doesn't have any.

The recommended "PLATE" and "LOAD" presets aren't very meaningful, except perhaps as a "starting point" for actual tuning.  Depending on your load (antenna), amount of drive power and section of each band you're operating, the final tune settings are likely to be very different from the starting points.

Low grid current is indicative of improper tuning, almost always.  The GRID current will "peak" as you rotate the PLATE tuning control to peak the output power, and when output power is peaked to max, the GRID current will also be max.  The LOAD control can be advanced to increase output power (unless it's already too far advanced) and that will REDUCE grid current.  The two controls are interactive and usually required 2-3 touch-ups before output power is finally peaked.

But without a wattmeter, it takes a more experienced operator to tune that amp.  I'd definitely get a wattmeter and put it in line after the amplifier; then you'll see the interaction between actual output power and the AL-811 meter indications.
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N3DT
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Posts: 1790




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« Reply #12 on: November 14, 2014, 11:45:13 AM »

Just curious, but doesn't the al811 measure both Ip and Ig? The Ip should dip while the Ig peaks. I don't know how you can tune an amp without knowing Ip, other than output watts. I guess that's the nice thing about the AL80B is you can watch Ip, Ig and PO all at the same time. But I still like my LP-100A better for PO.
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KM1H
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« Reply #13 on: November 14, 2014, 11:47:01 AM »

A safe and sane power for even USA made 811A's is 150W out per tube, this goes back decades to the Collins 30L1, Heath Chippewa and others.
With them a little anode color during tuning or voice peaks wasnt fatal.

OTOH the Chinese versions have thinner sheet metal plates that easily burn thru or develop hot spot discoloration plus Ameritron/MFJ intentionally increase filament voltages and specs to meet advertised specs set by the marketing weenies.
I get a lot of those 3 and 4 tube amps in here for service and always rewire the transformer primary leads for no more than 6.3VAC at the socket with all tubes lit up at a nominal 123VAC input and let the HV fall where it may which is under what the manual calls normal.
There are far less tube arcs also and about 15W drive per tube should not be exceeded.

If the Ig is watched and fully peaked AND kept within spec that is an excellent indicator of proper tuning, a wattmeter is an optional accessory but useful when it includes a VSWR function.

The 4 electrolytics are also running close to the limit as shipped and often fail from power surges; a 100V or less HV is an additional safety overhead for an amp that is marginal in all respects to start with.

Upgrading to an AL-80B brings the same overvoltage filament to meet an outrageous PEP spec. It is a fairly good amp when the drive and currents are run within the tube manufacturers specs, not MFJ's hype and control over Ameritron.

Carl
« Last Edit: November 14, 2014, 11:49:31 AM by KM1H » Logged
W8JX
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Posts: 13268




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« Reply #14 on: November 14, 2014, 02:06:28 PM »

A safe and sane power for even USA made 811A's is 150W out per tube, this goes back decades to the Collins 30L1, Heath Chippewa and others.

I fully agree. I have long said that the 3 tube 811 amp was a good up to 450 watts and the 4 holer good for up to 600.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
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