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Author Topic: al-811h load control fully clockwise on 80m  (Read 12675 times)
K4RVN
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Posts: 261




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« Reply #15 on: May 12, 2016, 06:02:11 PM »

Steve, no respect or answers for you just like Rodney. LOL
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K7MH
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Posts: 455




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« Reply #16 on: May 12, 2016, 06:32:30 PM »

I had the same problem with an older AL-811. Had to add more padding. It's a common problem. I don't remember what I added but an email to Ameritron solved the problem.
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WY7CHY
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« Reply #17 on: May 12, 2016, 06:40:42 PM »

I had the same problem with an older AL-811. Had to add more padding. It's a common problem. I don't remember what I added but an email to Ameritron solved the problem.

The sad thing is; I've been on back and forth emails with Ameritron for the last couple days. I can't say that they were all that helpful. First, they suggested that I look at the "Tank Circuit" and power supply board. They wanted me to make sure the coil hadn't gotten too hot and part of the loop hadn't welded to the next loop and changed the capacitance. Ok, I looked. Looked normal.

Then, when I told them it looked good, they wanted my to check diode D-16 and the 2 resistors on the same board. I replied: "Isn't D-16 related to the meters? If D-16 was a problem, wouldn't that affect ALL BANDS and not just the 80m". Their reply.... And I QUOTE, because it's CLASSIC:

".......if the diode was bad the grid would be too high on all bands resulting in the load being out of tune. Evidently you have something going on with that tank circuit coil. Best regards".

I'll reply to them again with your comment about having to "Add more padding" and that it's a common problem. I'll see what they say. Thanks. Mike.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
K4RVN
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Posts: 261




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« Reply #18 on: May 12, 2016, 08:14:31 PM »

Mike,
I own an AL 80 B and an A. I would suggest that you connect that amp to a dummy load like WB2WIK suggested and asked do you own one. I believe he also owns an AL 80 B. It sounds to me like you may have an antenna problem on that band. The 50 ohm dummy load will eliminate the possible antenna problem and let you know it is an amp problem.
Good luck,

Frank

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WY7CHY
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Posts: 953




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« Reply #19 on: May 12, 2016, 10:17:27 PM »

Trust me, I have used a dummy load. This isn't my first rodeo. But for what it's worth, I'm using an external antenna tuner, so the amp doesn't see the antenna anyway. Is sees the 50 ohm load of the tuner. The main reason for tuning into a dummy load, is: A) You don't have a tuner; and B) You don't piss off everyone on the frequency who might be trying to use it. But again, there is not difference at all.

Tuner and antenna; or dummy load, the results are the same. Start at 10 watts into amp, plate and load seem to do what they're suppose to. RF Out peaks, plate dips, adjust load for max RF out. Go up to about 20-30 watts into amp. Plate adjusts like it's suppose to. Don't have to budge it much at all. Load, has to go higher to get the RF to peak higher. From 3-ish, to around 5-ish. Go up to 40 watts input to amp, same thing. Plate doesn't need much budging. Load is up around 7-8. To get 50 watts in, load has to be maxed out at 10 to keep the grid current in the safe zone. I can push a little more RF power into the amp, but then I'm pushing the grid current because I have no more load capacitance to work with.

And it's exactly the same with a dummy load. Which it SHOULD BE when using a tuner. With an antenna tuner, the amp never sees the antenna. "Assuming of course that the tuner can tune the antenna". Which mine can.

This isn't the end of the world. I can get 450-480 watts out on 80m. SWR between the transceiver and the amp is real good. I keep the grid current and the plate current below the max. (I back off the power a little bit). I mainly use 80m for local daily Net Traffic. "The Loop antenna is pretty NVIS on 80". But ALL the other bands work fine. I even tried the bands I never use. 40, 20, 17, 15, and 12 meters were all good. Good power, good SWR to exciter, Plate and Load settings are very close to what the manual says. All is good. Spoke to Venezuela, Guatamala, Puerto Rico and St. Croix today on both 20 and 15 meters. I can use the 80 meters. Just at reduced wattage. "Around 400-450 watts". Which is fine That means SSB is around 600 watts. (If my PEP meter and math are right). Even on the good bands, I never run full. I run about 500 watts cw. Which is about 650-700 watts on SSB.

I've passed on the "Padding" info to Ameritron. We'll see if they reply back with any suggestions. I haven't de-soldered the caps on the bandswitch to test them. It could be a bad cap. I don't think it's the tank coil. That looks really good. But it's all ok. All is good. If we can figure it out, we will. If not, it's not like I don't have use of the 80m band. Thanks for all the input. Mike.
 
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
WB2WIK
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« Reply #20 on: May 13, 2016, 09:41:40 AM »

If your amp on 80m "peaks" at "full loading" (which is MINIMUM load capacitance, not maximum), how could adding more padding capacitance help?

Should be just the opposite: There's already too much padding capacitance, you'd need to make it smaller.
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WY7CHY
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Posts: 953




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« Reply #21 on: May 13, 2016, 11:48:39 AM »

Technically, I agree. Usually, adding "More Padding" is for those who have the opposite problem where they have the load set to 1; not 10. But I was going on the post by K7MH who said he had the exact same problem, and he had to add more padding.

In my situation, I looked and I have the 3 caps on the bandswitch. Normally, it's 2 caps, and some people have had to add the 3rd capacitor. (According to Ameritron). I already have the 3 capacitors. Now, without unsoldering them, it is possible that one of the caps have gone bad, and it's influencing and affecting the load. "Just a stab in the dark -I haven't unsoldered the caps to test".

I'm also wondering something else. "Again, a stab in the dark". I've heard of individuals who have had some issues with their amp when they "Cut the green wire" to allow the amp to work on the 10m band. I know that has been done on my amp because I saw the cut wire and I'm also able to tune up on 12m. (It shares the circuit with 10m). Is it possible that the 10m mod is affecting the 80m loading? Again, just a stab. If that's the case, that's a real easy fix. Reconnect the cut green wire. I NEVER us 12/10m bands. I use 15/17/20/40/80 meters exclusively. Anyway; just a thought. Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W1QJ
Member

Posts: 2944




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« Reply #22 on: May 13, 2016, 03:45:45 PM »

Mike, making "stabs in the dark" is not the way to diagnose a problem.  Once you get to bands above 40 meters the load control hovers around the middle of the dial for all the rest of the bands.  Only on 160 and 80 meters does the load control tend to be more toward 1 to 3 on the load dial (full left almost)  If your dial setting on the load is toward #10 the "truth table" dictates that your load variable cap is set up opposite than it should.    You need to open the amp up and look and see if the load cap is fully meshed at #1 on the dial, which t should be.  If you are getting the most output at #10 it has to be just the opposite and the load cap is meshed fully at #10.  If you set it properly the 80 meter power and 160 meter power will be peaked in the 1 to 3 range on the dial.  Can you do this?  The truth table dictates this is your problem and since all the other bands tend to peak at half scale, it would not matter which way it was set it would be about right in either case.  Lou
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KK5DR
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Posts: 631


WWW

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« Reply #23 on: May 13, 2016, 04:43:00 PM »

If you get a clearly visible peak in RF power out, it doesn't matter where the knob sets.
If you want your 811 tubes to last, run them like Collins did in the 30L-1.
500 watts out, they last decades. Anymore than that, and you are greatly shortening the life span.
Pretty simple.
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WA1RNE
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Posts: 1010




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« Reply #24 on: May 14, 2016, 07:17:41 AM »

 You're getting some good advice, especially being more methodical about the troubleshooting process.

 i.e. using a dummy load to eliminate a variable in the troubleshooting process.

 The purpose of the adjustable pi network is to allow the amplifier to operate into a range of load impedance while keeping the tubes within their safe operating parameters.

 In your case, the load control is near 10 on the scale which corresponds to maximum loading (minimum capacitance) on 80 meters and near full output, so the output impedance is clearly well away from 50 ohms resistive.

 If this amplifier was at Ameritron for repair, what's the chances the technician would be using an external tuner and antenna for a load to troubleshoot your issue? Pretty slim because he would be going against standard procedures.

 The dummy load also eliminates another possibility:  at increasing power levels your tuner and antenna may be failing, i.e. a component may be arcing or overheating, once again causing amplifier to see a load impedance outside of it's operating range.

 After you have completed that step - and presuming the amplifier still loads incorrectly - you should feel confident that external variables have been eliminated and it may be time to start looking for problems in the amplifier.

 ...WA1RNE
 
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WY7CHY
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Posts: 953




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« Reply #25 on: May 14, 2016, 08:30:47 AM »

Rne. I appreciate the input. But if you read back a post or two, you'll see that I have tuned it into a dummy load. As well as to a tuner which in the eye of the amp, is also a 50 ohm load. Dummy load or tuner results in the exact same thing.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W3RSW
Member

Posts: 606




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« Reply #26 on: May 14, 2016, 05:31:15 PM »

C's 23, 24, & 25 ( 360, 500 & 360 PF respectively at 1kv) are your auxiliary switched in loading caps.  Check to see if they are in correct order and that all three go to correct band switch taps.  I can see one case where a 500 PF has been switched in erroneously where a 360 PF was expected.  You would then see an additional 140 PF load where none was designed for that tap. Curiously on 160 meters , by proportion the same error of almost wrong cap might not affect the dial or mesh error of the variable cap much as on 75/80.

For that matter, factory could have put wrong values in one or more of these caps in a series of builds.  Even if right, Trying to get a spread all across the 75/80 meter band in conjunction with using two of the same caps on 160 may simply have caused Ameritron to degrade 80 to 500 watt nominal by picking L net coil tap to marginalize 80.  No one's later resoldered the 80 coil tap have they?   Does your plate voltage and current the yield the same power supply input wattage as on the other bands ( within reasonable error) to get 500 watts output on all?   --Etc.  So, stuff to look at , measure and try.
 
Those DM load caps ( yellow  1kv  flat caps ) clustered around the band switch look pretty flimsy to me current wise, ...probably are marginal but ok in parallel on 160 at the 500 watt level, at little from nominal mismatch that is.

Another thing I'd try is to inspect, measure C3, C4 and L1 of the input network.  May simply be a miss valued cap place in a series of amps, wandered or mistuned slug value of L 1, etc. or did you say you already peaked up the slug from the rear....  Will be very broad.
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Rick, W3RSW
W1QJ
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Posts: 2944




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« Reply #27 on: May 15, 2016, 04:13:10 AM »

I don't believe the OP has confirmed if the load control is set properly with the log scale, that being maximum capacitance at the ZERO point on the log scale as it should be.  My guess is someone switched it.
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W3RSW
Member

Posts: 606




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« Reply #28 on: May 15, 2016, 04:48:15 AM »

Well then how could the loading knob give the right table readings on all the other bands as the operator has already noted? 

If he hasn't already, opening the cabinet again will reveal lots of info ncluding the cap's mesh and yellow flat caps arrangement.  Grin
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Rick, W3RSW
W1QJ
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Posts: 2944




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« Reply #29 on: May 15, 2016, 05:01:24 AM »

Well then how could the loading knob give the right table readings on all the other bands as the operator has already noted? 

Good question, go back and look at my comments on this thread.  probably up a few here on page 2.  I discuss that very question you just asked.  Grin Grin Grin Grin Grin
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