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Author Topic: what did i do wrong?  (Read 34827 times)
AE7IS
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Posts: 96




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« Reply #15 on: November 14, 2014, 02:40:10 PM »

thanks for the input , but i must confess i am a bit more confused.  I get that the plate and load points are just the starting points.  I also must admit that I tried changing both (one at a time), increasing and decreasing.  My grid reading didn't change.  not a bit.  only when I brought the plate voltage up to the red area did my grid meter go up and then only to perhaps 75 (i didn't hang around to see where it would stop...chicken)  tried with the alc unhooked and hooked up no difference.  I will try the test with the builtin tuner tonight and see.  So far no smoke and i would really like to keep it that way.  Im not trying for 600 or even 500..400 would be nice tho.  some have said that a watt meter is required, others say not needed.  so how would i tune without some indication of power out?  is that what the grid meter does? kinda? sorry being so stupid  wanted to get that tot thing that tof unit from w8ji.  seemed like it made it pretty straightforward...unfortunatly he hasn't finished the instructions yet. i keep thinking that maybe the tubes are "soft", i did get this used?  anyway to tell?
one more time, thanks so much for the help  its all a learning experience
frank
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WB2WIK
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« Reply #16 on: November 14, 2014, 03:29:54 PM »

thanks for the input , but i must confess i am a bit more confused.  I get that the plate and load points are just the starting points.  I also must admit that I tried changing both (one at a time), increasing and decreasing.  My grid reading didn't change.  not a bit.  only when I brought the plate voltage up

You are confused!  You can't adjust the plate voltage in that amp.  It's whatever it is.
Quote
to the red area did my grid meter go up and then only to perhaps 75 (i didn't hang around to see where it would stop...chicken)  tried with the alc unhooked and hooked up no difference.  I will try the test with the builtin tuner tonight and see.  So far no smoke and i would really like to keep it that way.  Im not trying for 600 or even 500..400 would be nice tho.  some have said that a watt meter is required, others say not needed.  so how would i tune without some indication of power out?  is that what the grid meter does? kinda?

No, that's not what it does.  Grid current is a good tuning indicator but doesn't provide any indication of output power.

I've seen some on-line YouTube tutorials on tuning that amp, but the ones I've seen weren't very good.  Too much talk and not enough doing it. Cheesy

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KM1H
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« Reply #17 on: November 14, 2014, 05:01:37 PM »

Go to a relatively safe band such as 40 or 20M.

Start with about 30W drive and watch only plate Current and grid Current

Starting with the manual settings adjust just the Tune knob, you should already have some somewhat midscale plate current at this point.

If there is no Grid current then Decrease the Loading by Increasing the caps capacity; this part confuses many as it is counter intuitive. In that and most amps that will be to a Lower dial scale number.

Tweak the Tune control a bit to try and find the resonance sweet spot on the Grid meter. If you get Grid current and its too high reverse the Load control a bit to bring it down and then peak again with the Tune control.

IGNORE the manual here and do not exceed 150 ma Grid current at any time except for a second or so during tuning. The 811A and 572B are 50 ma per tube devices. MFJitron lies again of course and wants the same Grid current as the AL-811H. It really is 200ma for the AL-811H.

Once youre in the ballpark bring the Load control to a higher number until Grid current is a very low amount at 30W.

Now slowly increase drive to about 45W and always use the Load control to keep the Grid current in spec.

Finish up by slightly tweaking the Tune control to peak Grid current and the Load control to keep it under the 150 ma.

Your output will be about 450W at 45W drive indicating a 10 dB power gain. Forcing the tubes to 600W gets you another 1.25dB, not enough to even hear much less beat on the tubes.

Carl
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KH6AQ
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« Reply #18 on: November 14, 2014, 05:14:43 PM »

You do have a wattmeter, right? One is required to tune this amp.

Follow the tuning instructions on page 6 of the manual and as it says don't exceed 200 mA of grid current.
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KM1H
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« Reply #19 on: November 14, 2014, 06:20:11 PM »

A. He already said he doesnt have a wattmeter.

B. One isnt NEEDED to tune an amp

C. The manual is wrong for the 3 tube AL-811

Carl
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K0ZN
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Posts: 1862




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« Reply #20 on: November 14, 2014, 08:21:34 PM »

OK.... maybe I can help.  I have a 3 tube AL-811.

The cold hard fact is you really, really should have an RF watt meter to tune up that amp. It *can" be done other wise, but it is MUCH MUCH easier on you AND the tubes if you have a way to see relative RF output changes/increase as you tune. Although you *can* tune it without an output indicator you are likely making life difficult and or dangerous for your tubes !

try it this way:  on ~ 7.035 Khz:  Set the LOAD control to 1.8 and the PLATE control to 7.25.  Those will be "in the ball park", but probably not exact
on your amp. Key the amp (drive it) with about 28 watts RF. Tune (adjust) the Plate control for maximum OUTPUT. If you can't measure output, I would tune the PLATE control for a dip in the plate current. Adjust the LOAD control for maximum output. The re-adjust the PLATE for max. output. On CW you can drive it to about 400 watts output. If you cannot measure output, then do NOT drive it with more than about 32 watts.  HEED the warning in the book !!... don't hold it key down tuning it for more than about 5 seconds and let it cool for 15 between tuning sessions (until you get it down quickly).

If you want to tune up in the phone portion of the band, try around 7.280 Mhz. Use 3.6 on the LOAD control and 7.5 on the PLATE.  Follow previous instructions.
If you do not have an output meter, I would not drive it with more than about 40 watts.

Further to the above: on 20 M try 14.280 or so and use 3.1 on the LOAD and 8.6 on the PLATE.  (Again, your amp will likely give slightly different readings)

Make sure you are not tuning up on top of somebody's conversation/QSO !  Best way is a dummy load.

BUY a small hand mirror so you can easily and quickly look through the air vent hole in the left side of the cabinet and see what the color of the tube plates are.
Regardless of what Ameritron/MFJ says, the 811A tubes are NOT "tough"...they are rather fragile....especially the grids! KM1H is correct. DO NOT exceed 150 ma of grid current!!  The grids in 811A's are very tiny, fine wires; they won't take much abuse.
You WILL ruin the tubes quickly if you run excessive grid current.  

DO NOT operate the amp if the tube plates "glow" more than a very dull red. Bright orange is BAD ! You WILL burn a hole in the tube plates rather quickly if you run them too hot.

IF you see the EITHER meter going into the "excessive" area IMMEDIATELY unkey (turn off the drive power) to the Amp and figure out WHY the current is excessive....probably related to too much drive power or grossly incorrect PLATE or LOAD controls....or wrong band !

It initially seems like it is "difficult" to tune an amp, but once you get the hang of it , it is easy and quick.  LOG the reading of the controls along with the drive POWER
that gave those control settings.

FYI:  If you are technically inclined, you can also build a simple RF field strength meter for an output indication.  A stronger signal is more RF output !

I also had to go into the INPUT slug coils in the back and re-tune them....from what i can see is you get a CHOICE of EITHER 18 or 15 and EITHER 30 or 20.
I am a little concerned about the stability of that amp on the higher bands, so I tuned the input for 1:1 on 18 M...and essentially lost 15....by choice. (I got the feeling that amp was operating "on the edge" stability wise on 10 M, so I stay off of 10 with that amp....but that is an opinion and not a fact.)
FYI: tuning control settings get EXTREMELY critical/sensitive on the upper bands. "plan accordingly".

I had "fits" with my AL-811 when it was new. (failures in tubes, a failed diode and a mis-wired tank coil !! ...see my reviews in the eHam review section.)
After getting all that stuff sorted out.... it has run very reliably. I do not "push it".... I run mostly CW and have found that the tubes seem to be "happy"
at about 375 watts output on CW... and that is still "pushing it" to some degree. On SSB you can get more; 500 OUTput is probably fine on SSB, but don't push it on CW, data or RTTY modes. The 811A only had 65 watts of plate dissipation in ICAS (intermittent) service. In continuous service (such as RTTY or DATA or FM, etc.) they are rated at 45 watts of plate dissipation ! The AL-811 is a very inexpensive design....you trade a lot of stuff to get a low purchase price....one must understand that.

My guess is that MOST of the 811A amps are ruined are damaged by improper operation and/or over drive by hams who don't understand tube type amplifiers. This little amp will give decent service if you are KIND to it ! What fascinates me is that I also have an Alpha and I have found that I can work (mostly CW) about 85% of the DX stations with the AL-811 that I can work with the Alpha.....so, bang for the buck is really very good!

Good luck!   73,  K0ZN

P.S.   again... GET an RF output meter....it will save you a ton of troubles.  


« Last Edit: November 14, 2014, 08:44:24 PM by K0ZN » Logged
K4RVN
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Posts: 261




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« Reply #21 on: November 14, 2014, 10:11:55 PM »

Frank, You need to listen to WX7G, and WB2WIK and K0ZN.  I agree with them that you need a watt meter to tune the AL811 as I owned one for three years that I bought new. Use about 20 watts to tune the AL 811 for max out on a watt meter connected to your good antenna that you mentioned with a low SWR. Make sure you use the presets as a starting point then tuning the amp with 20 watts until you get the max out on your watt meter. Make sure you don't unload the load setting down toward zero. After getting used to loading the amp with 20 watts, then turn up the drive to about 55 watts which should give you about 500 watts. Don't try to max the amp out unless you want to buy some new tubes due to the long tuning time and exceeding the tubes ratings for extended periods. I can tell you as a former owner of the three tube 811, don't try to operate or tune the amp without a watt meter. I don't pay much attention to the meters on the amp when tuning unless they go way too high. Getting used to tuning the amp at lower drive and power out will allow you to put out 200 to 300 watts or more and I would suggest that you make a few qsos with the amp
at lower power so you don't blow something. 

Frank
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WA7PRC
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« Reply #22 on: November 14, 2014, 10:44:49 PM »

I agree with them that you need a watt meter to tune the ...
For decades, I used only an inexpensive and super easy to use oscilloscope to tune my SB-220. An advantage is, when using SSB, it indicates if I don't have the amplifier loaded enough or if I'm overdriving it (either case causes splatter). NO meter will indicate that. W2AEW shows how he does it in this video clip.

vy 73,
Bryan WA7PRC
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K4RVN
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« Reply #23 on: November 15, 2014, 07:40:22 AM »

By the way Frank, your plate voltage is not adjustable during the tuning process as it is fixed once your input power to the amp is selected.  I think you were talking about the plate current in your post. The plate voltage can be monitored, but not adjusted. At any rate, the amateurs I mentioned in my post know what they are talking about and I would like to think I do having owned the specific model amp you have for three years no problems with tubes. You need a simple watt meter to use this amp and even a radio shack 40 buck one will do, but suggest you get one for the long term if possible. I own three watt meters plus have one in the tuner plus one on my AL 80 B. The cross needle ones show reflected power and forward power at the same time. That will let you know when your antenna or connector cables have a problem at a glance when your power out is reflected.  You are unaware of your power out from the amp to the antenna without a watt meter. Good luck I know it's confusing, just keep it simple and enjoy the hobby. I also owned a 590 for a short time and used it to drive the AL 811 so not a stranger to your set up. You may have already damaged your tubes with improper delayed tuning times, but I hope not.

Frank
« Last Edit: November 15, 2014, 07:43:56 AM by K4RVN » Logged
AE7IS
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Posts: 96




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« Reply #24 on: November 15, 2014, 10:19:27 AM »

thanks for the input. (pun)  a watt meter is on the list.  and I won't play with the amp until I get on.  MFJ-891 okay?  thats about 150  or so . (half what i paid for the amp)  it is what it is.
frank
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AE7IS
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« Reply #25 on: November 15, 2014, 10:23:47 AM »

one more thing if I may.  I asked on this forum because the responses i get are actually helpful, not demeaning.  Unlike that "other forum".  I don't ask these kind of questions there anymore..  Very nice to have you all here and willing to help.  even when you disagree it never gets bad or derogatory. 
Just wanted to acknowledge.
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G3RZP
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« Reply #26 on: November 15, 2014, 10:59:43 AM »

I'd strongly suggest that a power/SWR meter and dummy load are really essential items to have, even without an amplifier. Otherwise, fixing many of these problems is rather like trying to take the engine out of a car without having a set of wrenches!

I have a feeling that the Licence Courses often miss this sort of advice out.....
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AE7IS
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Posts: 96




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« Reply #27 on: November 15, 2014, 11:29:52 AM »

  ZP,I didn't take any stinking lic. course.  didn't know they had such a thing until after i was an extra.   nope, even after 40-50- years playing with radios and I didn't know that a watt meter was essential to do anything.  Guess I've been lucky so far. 
thanks
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WA7PRC
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« Reply #28 on: November 15, 2014, 12:10:55 PM »

I didn't know that a watt meter was essential to do anything.
As I mentioned, it's not. However, an inexpensive and easy to use oscilloscope is a very handy tool for ensuring you're not underloading and/or overdriving your amplifier on AM or SSB modes. Otherwise, for other modes, tuning for maximum power works using some form of meter.

A suitable lab scope should have a vertical amplifier response of at least twice the radio frequency. For 10m, a 60 MHz scope is fine. A fair price is around $1/MHz.

vy 73 es gl,
Bryan WA7PRC
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AE7IS
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Posts: 96




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« Reply #29 on: November 15, 2014, 05:55:07 PM »

l'ld love to pick one up bryan.  Any idea where i could find such a thing at the price you mention?  As an aside, I went to RS today looking for a watt meter.  Guy tried to point me to the multimeters??.  needless to say they had none.
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