Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1] 2 3 4 5 6 Next   Go Down
  Print  
Author Topic: AL-811H Lost Plate Current  (Read 13584 times)
WY7CHY
Member

Posts: 1018




Ignore
« on: August 11, 2016, 09:32:28 PM »

My AL-811H has been working great. Today, I turned it on, let it warm up for a minute or two like always. Preset the band. Transceiver was tuned properly. Matter of fact, I was just talking on it barefoot and it's fine. Put the Amp in operate mode so I could tune it. I use a pecker and SSB, so it's not like I put a lot of power into it. I key it up and I "THINK" I heard something different; can't tell. But no plate current at all. Plate voltage is around 1650. (That's normal for it). Grid current goes high. (Higher than normal). Grid current does change depending on how much rf I put in. But no plate current.

I disconnected the ALC. I lowered the transceiver to about 20 watts. Changed tuning to RTTY instead of SSB/Pecker. Still no plate current. If I push more than 30 watts into the amp, the grid current will max out. 

If it was a tube, I'd think there'd be some plate current and some output. Any ideas?

Thanks. Mike.
Logged

Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W1NK
Member

Posts: 658


WWW

Ignore
« Reply #1 on: August 12, 2016, 02:50:02 AM »

http://www.w8ji.com/ameritron_811h_572_amplifier_trouble_shooting.htm

See #12 on the list.  Sounds like your plate choke opened up.  If that's it, it's simple to swap out the bad choke for a good one... if I can do it, anyone can do it!  Cheesy

Frank, W1NK
Logged
W1QJ
Member

Posts: 2984




Ignore
« Reply #2 on: August 12, 2016, 03:59:08 AM »

Yes, it could very well be the plate choke opened or a glitch resistor if someone put one in.  Do this test.  See if the HV meter goes down when the amp is in transmit with no drive.  Just keyed.  The HV meter should go down a bit.  If it doesn't budge the there is no voltage on the plates of the tubes, hence an open B+ line
Logged
W8JX
Member

Posts: 13268




Ignore
« Reply #3 on: August 12, 2016, 04:28:40 AM »

Yes, it could very well be the plate choke opened or a glitch resistor if someone put one in.  Do this test.  See if the HV meter goes down when the amp is in transmit with no drive.  Just keyed.  The HV meter should go down a bit.  If it doesn't budge the there is no voltage on the plates of the tubes, hence an open B+ line

Very good tip for a quick check of plate choke. If choke is gone though he may have a shorted tube that popped choke. If blown pull all tubes and use a ohm meter to check plate to grid and plate to filament for shorts.
Logged

--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
Member

Posts: 1018




Ignore
« Reply #4 on: August 12, 2016, 06:36:23 AM »

Thanks for the replies. I hope it's as simple as a blown plate choke. Those are pretty simple to replace. As I mentioned previously, at first I though I blew a tube. But even with a tube gone, I should have had some plate current. Unless the tube shorted. Thanks for the ideas. I'll get looking at it tonight. Thanks. Mike.
Logged

Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
Member

Posts: 13268




Ignore
« Reply #5 on: August 12, 2016, 07:52:42 AM »

Thanks for the replies. I hope it's as simple as a blown plate choke. Those are pretty simple to replace. As I mentioned previously, at first I though I blew a tube. But even with a tube gone, I should have had some plate current. Unless the tube shorted. Thanks for the ideas. I'll get looking at it tonight. Thanks. Mike.


A blown tube would reduce plate current but not zero it out. A shorted tube if you are lucky with blow a fuse or choke before it does more damage.

On a side note  I am not a fan of a "pecker" for tuning. You are better to tune without it and limit key down to 5 seconds or less and then wait same 6 to 8 seconds or more and repeat until done. The 811 is a LD amp at best due to it easily exceeding the ratings of the 811 tubes in it and therefore easy to damage during tuning and operation as well and using a pecker can induce a false security tuning it too. You have to remember that key down idle current the tubes are pretty much at max rated dissipation ratings before modulation (and many do not realize this) which pushes tube well past limits while "pecking" with no zero current idle time. This means that tubes will still over heat with pecker after 8 to 10 seconds vs with method I suggest which during 6 to 8 second pause during tune cycle there is zero current and tubes can shed some heat before next key down.  Also I am not at all convinced that pecker tuning method is less stressful on amp than as I suggested above. I suggest if a tube(s) is indeed bad that you scrap pecker and install 3ea 572's and be done with it.
Logged

--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
WB2WIK
Member

Posts: 21837




Ignore
« Reply #6 on: August 12, 2016, 08:09:19 AM »

Certainly does sound like HV is not reaching the tubes.

Only other comment:  No reason to wait a minute or two for this amp to "warm up."  811As "warm up" in less than three seconds and are ready to go.   Waiting longer doesn't do anything except run up your electric bill a little bit more.
Logged
WY7CHY
Member

Posts: 1018




Ignore
« Reply #7 on: August 12, 2016, 08:37:02 AM »

Only reason I wait a minute or two, is usually because if I'm using the amp, it usually am going through the transceiver to make sure I don't have it set for max power; make sure the antenna tuner is tuned, etc. Probably not really 2 minutes.

As for the pecker; even with it, I never leave it keyed more than 5 seconds. I've gotten use to WHERE the AL-811H settings are for plate/load, that it's pretty much 90% tuned before I key it with the pecker.

As for the tubes, they are new. Only had them in a couple of months. Well actually, they're NOS. Russian G-811. Very good tubes. I'm hoping that the plate choke just blew. I didn't blow any power fuses. All 4 tubes still light up. Can't really tell if any of the tubes are bad. Worse comes to worse, I still have the old tubes I had in it before replacing with these a couple months ago.

When I get home tonight, I'll pull the tubes and measure the choke to see if it's open. If it is, I'll order a new one. This choke is the original, and I noticed that the winding are a bit loose. They don't cost that much. If I order a new choke, I might consider a new parasitic while I'm at it. My AL-811H has the old style tube caps with the wound resister in series to the cap; instead of a board. Also; even though it's the "H" model (AL-811H), I noticed that the HV Caps are 210uf instead of 270uf. According to all the ameritron info I've read, only the original AL-811 used the 210uf. Supposedly the "H" and later models of the AL-811 used the 270uf. I might replace them while I'm at it.

I'm just Hoping and Praying that it's just the plate choke. This has been a good amp. Got it from a friend of mine about 6-7 months ago. I've liked it. I hate thinking I might spend weeks or longer trying to troubleshoot it. I opened it up, and visually, everything looks fine. Didn't see anything burnt, black, open, etc.

I'd like to be able to test the tubes, but not quite sure how to accurately test those. And if a tube is shorted, and it is what blew the Plate Choke, I'd hate to put in the new choke and the tube would blow the new choke. Any idea on how to do a basic test on the tubes?
Logged

Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
Member

Posts: 13268




Ignore
« Reply #8 on: August 12, 2016, 08:54:36 AM »

Russian or Chinese a 811 tube is only rated 45 watts continuous dissipation which is very LD for a amp. A 572 is rated over 3x that to put it into perspective. When you use a AL811 you are play Russian roulette with tube life. How many "bullets" are in "gun" depends on how much output from tubes.

On resetting drive level, I run the same power barefoot that I use to drive amp. If 50 watts does not cut it neither will 100 on HF most of the time. On nice thing about doing that way is that going from 50 to 400 watts is nearly a 10 db jump vs a single S-unit from 100 to 400 watts. (in my case I go from 50 to about 1000 watts or 13 db which is a solid two S-units)   
Logged

--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
Member

Posts: 1018




Ignore
« Reply #9 on: August 12, 2016, 09:10:09 AM »

Thanks for the replies.

Question. If I was to replace the 811A tubes, and you recommend using the 572b, why would I only put in 3 tubes as you recommend? Why not 4 like I have in there now?

Thanks. Mike.
Logged

Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
Member

Posts: 13268




Ignore
« Reply #10 on: August 12, 2016, 09:20:17 AM »

Thanks for the replies.

Question. If I was to replace the 811A tubes, and you recommend using the 572b, why would I only put in 3 tubes as you recommend? Why not 4 like I have in there now?

Thanks. Mike.


Because you power supply cannot begin to exploit 4 of them and you will get just as much power safely with 3 as you are power supply limited here. It is a waste of money to use 4. To put it into perspective, 4 811's are rated a max plate current of 700 ma. 3ea 572' are rated at 825 ma which is at limits of your power supply.
Logged

--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
Member

Posts: 1018




Ignore
« Reply #11 on: August 12, 2016, 09:30:43 AM »

Interesting. Thanks.

3 things.....

1) I'd still get the same 800 watts PEP/SSB that I get now with the 811A's?
2) Would it matter which of the 4 tube slots I leave empty? Is there a certain order?
3) The AL-811H normally has neutralization. With only 3 tubes in, will there be any affect?

Thanks. Mike

P.S. If I do the 572B, and I need a new plate choke for my current problem; I was thinking of getting a new parasitic. Would I get the 3 tube model like for the AL-811 instead of the 4 tube model for the AL-811H that I have?
« Last Edit: August 12, 2016, 09:34:22 AM by WY7CHY » Logged

Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
Member

Posts: 13268




Ignore
« Reply #12 on: August 12, 2016, 09:53:54 AM »

1) I'd still get the same 800 watts PEP/SSB that I get now with the 811A's?

Yes but 800 watts PEP is exceeding your 811'a ratings by a good bit. Roughly 50% of rated output power is dissipated in tubes so at 800 watts out you dissipating 400 watts or more than 50% more than 4 tubes CCS intermittent ratings of 260 watts total. (those amps are badly over rated for sales hype) 3 ea 572's are rated 480 watts dissipation continuous.

2) Would it matter which of the 4 tube slots I leave empty? Is there a certain order?

Which ever give best airflow over tubes

3) The AL-811H normally has neutralization. With only 3 tubes in, will there be any affect?

If needed you can re neutralize it

P.S. If I do the 572B, and I need a new plate choke for my current problem; I was thinking of getting a new parasitic. Would I get the 3 tube model like for the AL-811 instead of the 4 tube model for the AL-811H that I have?

Good question. 3 tube will work fine but you will have to use tube sockets that match it. If you use 4 tube you can leave one float if you every plan to go back to 811's (not sure why you would though)
Logged

--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
Member

Posts: 1018




Ignore
« Reply #13 on: August 12, 2016, 09:54:07 AM »

Back on topic.

As I asked previously, IF a tube had shorted, and that caused the Plate Choke to pop, is it possible that the tube is STILL SHORTED, and if I replace the plate choke, the tube could blow the new choke? Is there a way to somewhat test the 4 tubes; other than all 4 do light up?

Thanks. Mike
Logged

Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
Member

Posts: 13268




Ignore
« Reply #14 on: August 12, 2016, 09:58:07 AM »

Back on topic.

As I asked previously, IF a tube had shorted, and that caused the Plate Choke to pop, is it possible that the tube is STILL SHORTED, and if I replace the plate choke, the tube could blow the new choke? Is there a way to somewhat test the 4 tubes; other than all 4 do light up?

Thanks. Mike

As I stated earlier use a ohm meter to check plate to grid and plate to filament in each tube. 
Logged

--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
Pages: [1] 2 3 4 5 6 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!