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Author Topic: What Changes Would You Do To Your Ameritron 811/811H?  (Read 28752 times)
M0HDX
Member

Posts: 57




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« Reply #60 on: April 15, 2015, 04:50:52 AM »

I've loads of different tubes to choose from, but the all behave in the same manner. I've adjusted the input circuit, but with no joy.

I am contemplating buying an AL-80B and keeping the AL-811H as a standby. Wink

Hello ian, The main downfall are the junk 572b, s and 811, s coming out of china  nowdays, Many arrive DOA or produce low power out the box.I sold my Ameritron al811 and purchased a Acom 1000 and never looked back. Maybe a AL80B with a single 3-500z would be a better option.

Cheers jim M0HDX
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N9XTF
Member

Posts: 282




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« Reply #61 on: April 15, 2015, 05:27:16 AM »

Hi Doug,

I've just got round to read your reply there.

I'll strip everything back, but I'm not hopeful of a change as I've done this before.  I'll let you know how it goes.  The only time I noticed a major difference was when a patch lead that was about 8 feet long between the rig and the amp, on 10m the input SWR went haywire.  I soon figured out this was a quarter wave on 10m and was causing a problem.  I tend not to use patch leads of this length anymore and most of them as 18 inches or less made of reasonable quality RG58U coax cable that I've made up myself.

73,

Ian - MM0IMC.



Ian,

If your coax jumper length is changing the SWR significantly between the radio and amplifier, I would be very suspect of the jumper.  I only use RG-213 for jumpers and make them to fit between point A to B.  I have never concerned myself with resonant lengths; should not be a problem.  For antenna runs I use DX Engineering Flex 400.  Now on my 40M dipole, I use RG8X at legal limit without issue.  

At a minimum, I would use good quality RG-8X jumpers and see what happens.  The RG58U may not be shielded well and when soldering, you may be melting the dielectric, bringing the braid closer to the center conductor; possibly changing the impedance.   I use many different lengths of jumpers, long to short, and have never had an effect on the SWR on these runs; this makes me very suspect.

Choosing good quality cable and making sound terminations is very important and can cause all types of problems.  Others here with more knowledge will have better comments than I do.  If your jumper were resonant on 10M between the radio and amplifier, does it only cause a problem with the amplifier in operation?  I'm betting that the jumper has an issue and is picking up unwanted signal from the transmitted signal from the antenna or amplifier output.  

Make up some good RG8X, RG213 or 9913 jumpers and then do your test between the radio, amplifier and dummy load.

Doug - N9XTF
« Last Edit: April 15, 2015, 06:02:49 AM by N9XTF » Logged
KM3F
Member

Posts: 910




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« Reply #62 on: April 16, 2015, 06:52:05 AM »

Theoretically, if both ends of the patch cord are in good match to their loads and the coax is the same impedance, the length should not make any difference except for loss.
It all works the same as antenna matching.
However, as you talk the load impedance the amplifier presents can vary with dynamic drive level due to the dynamics of the tubes during their varying load/drive.
If swamping resistance is included in the input circuit it keeps the impedance change to a minimum.
If you test the 10 foot patch line on a flat dummy load and it measured flat then the amplifier load is changing over a wide range as you talk.
This may or may not be a fault depending on the amplifier input circuit design.
On my AL80B the load remains unchanged at any drive level.
You can use the radio's internal Tuner if you need by turning the amp on and hitting the auto tune button. It should match down the same as it would with an antenna.
Only difference you will see is the tuner presents a loss of about 10 watts +/- so you have to increase your amplifier drive level to get back to the output you want to run.
Good luck.
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KG6AMW
Member

Posts: 628




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« Reply #63 on: April 17, 2015, 07:55:42 AM »

I suppose improvements can be made.   Had my AL 811 amp for 15 years with few problems. In the first 3 years I replaced 2 tubes (1 tube due to rough handling and the other for heavy handed tune ups).  On year 13 I replaced all 3 Chinese tubes due to age.   Don't run over 400 watts SSB/CW, watch your tune ups and it will just run and run.       
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MM0IMC
Member

Posts: 255




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« Reply #64 on: April 17, 2015, 09:25:31 AM »

Hi Doug,

I've just got round to read your reply there.

I'll strip everything back, but I'm not hopeful of a change as I've done this before.  I'll let you know how it goes.  The only time I noticed a major difference was when a patch lead that was about 8 feet long between the rig and the amp, on 10m the input SWR went haywire.  I soon figured out this was a quarter wave on 10m and was causing a problem.  I tend not to use patch leads of this length anymore and most of them as 18 inches or less made of reasonable quality RG58U coax cable that I've made up myself.

73,

Ian - MM0IMC.



Ian,

If your coax jumper length is changing the SWR significantly between the radio and amplifier, I would be very suspect of the jumper.  I only use RG-213 for jumpers and make them to fit between point A to B.  I have never concerned myself with resonant lengths; should not be a problem.  For antenna runs I use DX Engineering Flex 400.  Now on my 40M dipole, I use RG8X at legal limit without issue. 

At a minimum, I would use good quality RG-8X jumpers and see what happens.  The RG58U may not be shielded well and when soldering, you may be melting the dielectric, bringing the braid closer to the center conductor; possibly changing the impedance.   I use many different lengths of jumpers, long to short, and have never had an effect on the SWR on these runs; this makes me very suspect.

Choosing good quality cable and making sound terminations is very important and can cause all types of problems.  Others here with more knowledge will have better comments than I do.  If your jumper were resonant on 10M between the radio and amplifier, does it only cause a problem with the amplifier in operation?  I'm betting that the jumper has an issue and is picking up unwanted signal from the transmitted signal from the antenna or amplifier output. 

Make up some good RG8X, RG213 or 9913 jumpers and then do your test between the radio, amplifier and dummy load.

Doug - N9XTF

Just to clarify, I use RG58U upto the point of the amplifier, after that it's RG213U. Wink  I've tried what you suggested regarding the direct connect to the amp missing out everything else, but I get the same results.  The RG58U I've used has a 95% screen coverage from what I can see, I make up the patch leads myself, not trust anyone else's work.

I've emailed some more info, including screenshots from my RigExpert AA-54 so you can see the input SWR that the rig sees on different bands from the amplifier. 

73,

Ian - MM0IMC.

« Last Edit: April 17, 2015, 09:49:13 AM by MM0IMC » Logged
MM0IMC
Member

Posts: 255




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« Reply #65 on: April 18, 2015, 04:18:23 AM »

Here's some screen shot I took from my antenna analyser the other day of the input SWR that the rig sees coming straight out the back on the amp...


160m input


80m input


40m input


20m input


15m input


12m input


10m input


12m-10m input wide scan


12m-10m input modified wide scan

The last two images show the difference before and after I increased the gaps in the winding of the 12m-10m input coil.  The same difference could not be achieved by moving the slug in and out.  What concerns me is that the lowest input SWR on that input circuit seems to be up at around 42MHz, even before modifying the input coil and using the standard silver mica capacitors that came with the amp...
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KM1H
Member

Posts: 5559




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« Reply #66 on: April 18, 2015, 08:38:58 AM »

Try disconnecting the tank circuit and plate choke and replace it with a 2K resistor to ground with as short leads as possible. I suspect your analyzer is "seeing" the plate choke which has a series resonance in the CB band plus the plate circuit.

Carl
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K8BDW
Member

Posts: 3




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« Reply #67 on: April 18, 2015, 10:11:58 AM »

Replace the 811's with 572 B's, which I did. Watch the drive however, the 572 will last forever using proper drive and not exceeding the power voltage inputs of the amp.
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W8JX
Member

Posts: 13268




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« Reply #68 on: April 18, 2015, 11:59:44 AM »

Replace the 811's with 572 B's, which I did. Watch the drive however, the 572 will last forever using proper drive and not exceeding the power voltage inputs of the amp.

Really not best choice especially if it is 811H as it lacks B+ current to properly heat plates to getter tubes. (AL811 and 811H use same power supply) With 3 tube unit you can run them at a higher current per tube than possible on 4 tube model and no way you can hurt 3 of them tuning.
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--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
W3RSW
Member

Posts: 606




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« Reply #69 on: April 18, 2015, 12:20:03 PM »

" what the rig sees coming out of the back (panel) of the amp"
Are not Those charts amplifier input swr's, somewhat removed from plate chokes, 2k resistor equivalents, etc.?  Grin   ...unless I drastically missed something, say backward current transfer ratio.

Amazing thread. Life of its own.
« Last Edit: April 18, 2015, 12:22:28 PM by W3RSW » Logged

Rick, W3RSW
G3RZP
Member

Posts: 1323




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« Reply #70 on: April 18, 2015, 12:29:59 PM »

The input impedance of a Class AB gg stage is dependent on input power level. At very low input levels where the tube is in Class A - likely to be those from an antenna analyser - it is 1/gm for each tube. When you get to AB2 and grid current, there's some argument as to what it is, but there's general agreement that it isn't a simple 1/gm..

Determination of input impedance really needs a dual directional coupler and a Vector Voltmeter on the input so the forward and reflected powers and relative phase can be measured over the full power range.
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MM0IMC
Member

Posts: 255




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« Reply #71 on: April 19, 2015, 07:49:28 AM »

I finally sorted this myself after over two years of trying...

The neutralising transformer's metal plates that are parallel to the valves (tubes) was far too close and compared to many photographs I've seen, to the point where they were rubbing up hard against the insulated connecting rod between the front and rear band switches.  Input SWR on 10m is now 1.1:1.
« Last Edit: April 28, 2015, 08:14:25 AM by MM0IMC » Logged
WA3YUR
Member

Posts: 3




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« Reply #72 on: June 10, 2015, 03:33:36 AM »

Thanks to those with actual input, and a valid reply to the query posed by the OP.
It's sad when people in the amateur community take it upon themselves to go full snark mode, and that they feel that putting themselves over makes them superior to the rest. Our hobby is already shrinking, and we need all the positive input we can get to keep the true spirit alive, and just maybe it won't be buried before we're all SK.
Again, I respect opinions, so why not help the community when someone has the interest enough to post a question at the risk of trolling or flaming?
If you want the contrary, youre free to start your own post on the topic of  how sh*tty you think that amp is, and you like minded ones can all pile on in your own confab; instead of hijacking a thread and going off- topic so the ones interested in doing something about it or contributing positively  don't have to wade through rants that don't assist the OP or the rest of us.
73

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W1BR
Member

Posts: 4196




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« Reply #73 on: June 10, 2015, 09:27:01 AM »

Replace the 811's with 572 B's, which I did. Watch the drive however, the 572 will last forever using proper drive and not exceeding the power voltage inputs of the amp.

Really not best choice especially if it is 811H as it lacks B+ current to properly heat plates to getter tubes. (AL811 and 811H use same power supply) With 3 tube unit you can run them at a higher current per tube than possible on 4 tube model and no way you can hurt 3 of them tuning.

We should look at the actual RCA spec's for the 811 tubes to see if plate current or color plays a role in gettering?

http://www.radiovilag.hu/images/811A.pdf

In CCS ratings they should  NOT show plate color... that implies that the plate temperature is not involved in the gettering process. The Chinese may have changed things, but I suspect the original 811 tubes were flash gettered during manufacture, as were the original 813 RF power tubes... another tube that is not designed to show plate color in CCS operation.

Pete
« Last Edit: June 10, 2015, 09:34:29 AM by K1ZJH » Logged
KE4ZHN
Member

Posts: 175




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« Reply #74 on: June 16, 2015, 09:45:13 AM »

Sell it and buy yourself a solid state amp. The era of tubes has come and gone. The terrible quality of Chinese tubes is fast making all tube type amplifiers junk. Russian tubes? The trade embargo against Russia killed that source at least for now. The Russian tubes aren't so great either. You can spend top dollar and buy the best amplifier designed or build it yourself...but if the tubes it must use are junk it makes the entire amplifier junk right along with it. After all, the tubes are the heart of the beast. If you like Eimac ceramics...good luck. May as well plan on the divorce when the XYL finds out what you spent on tubes for your amplifier. Another issue. I know a fellow ham who has a very nice commercially built amplifier that takes a GU84B Russian tetrode. These cannot be found anywhere. And IF you find one, the seller wants an arm and a leg for it with no guarantee it will even work since it's Russian military surplus. So now he has this gorgeous monster amp...that is a very expensive paper weight. He now has a solid state amp on order. Something else to think about. Since the military and many other industrial users don't use tubes anymore, how much longer will Eimac be able to stay in business making tubes? Their market share is dwindling at an alarming rate. High voltage MOSFETS are where it is at today.....like it or not.
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