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Author Topic: 10 mils of grid current AL-811  (Read 3990 times)
KB2OEV
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« on: November 06, 2016, 07:21:40 AM »

After installing W8JI TOF circuit in my AL-811 I now have a steady 10 mils of grid current showing when I power up the amp. This grid current stays steady at 10 mils even in standby. Current reads normal (approx. 150 mils) during operation.  Any ideas why this is and what affect it has on the amps ability to achieve full output?
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W1QJ
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« Reply #1 on: November 06, 2016, 07:24:45 AM »

That should not be.  Go over the installation instructions again carefully and make sure you did not make a mistake, check to solder bridges and miswiring.  Always double and triple check your work.
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KB2OEV
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« Reply #2 on: November 06, 2016, 06:17:04 PM »

Thanks, I did check everything and its according to the instructions. I guess I'll take it out and chalk it up to not a good addition.
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W9FIB
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« Reply #3 on: November 06, 2016, 06:19:54 PM »

Check to make sure all 811s are warm. I had something similar and found 1 tube not making good contact with the socket.
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73, Stan
Wisdom is knowledge you gain after you know it all.
K6AER
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« Reply #4 on: November 07, 2016, 08:56:10 AM »

Does the amplifier draw current with the tubes
removed?

Does the amplifier draw normal current when driven with RF?

Does the amplifier tune normally?

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KB2OEV
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« Reply #5 on: November 07, 2016, 02:15:06 PM »

I did not check it with the tubes removed. It seems to draw normal current when driven with RF but, I suspect I could get a few more watts out if I wasn't starting out with 10 Mils. It tunes normally. The tube are new Taylor tubes last week.  When I took the original tubes out one came apart on my hand (glass envelope was obviously broken.
« Last Edit: November 07, 2016, 07:02:59 PM by KB2OEV » Logged
KD6VXI
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Posts: 177




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« Reply #6 on: November 10, 2016, 02:48:20 PM »

The amp current draw with no tubes is a biggie.

If your getting an indication with no tubes,  that points to the TOF circuit being at fault or a faulty installation.

--Shane
KD6VXI
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KB2OEV
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« Reply #7 on: November 10, 2016, 09:29:37 PM »

Thank you . I'm going to try to check that this weekend.

Bob, KB2OEV
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KM1H
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« Reply #8 on: November 11, 2016, 05:48:11 AM »

There were several panic fix attempts with that amp which soon led to JI being let go. During one phone call to Ameritron it was stated they were already implementing fixes that JI's methods caused problems.

Carl
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VK3BL
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« Reply #9 on: November 12, 2016, 03:49:41 PM »

There were several panic fix attempts with that amp which soon led to JI being let go. During one phone call to Ameritron it was stated they were already implementing fixes that JI's methods caused problems.

Carl


Wow, outright slander and not even an attempt to help the original poster with their problem.

Nice showing of Ham spirit Carl.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
KM1H
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« Reply #10 on: November 12, 2016, 04:15:01 PM »

Trouble making Aussie, call Ameritron and ask them.

I thought I already helped him by explaining the possible situation affecting him.

Why dont you come to his aid instead of just being a TROLL??? Shocked  Angry

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VK3BL
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« Reply #11 on: November 12, 2016, 04:41:16 PM »

The amp current draw with no tubes is a biggie.

If your getting an indication with no tubes,  that points to the TOF circuit being at fault or a faulty installation.

--Shane
KD6VXI

The TOF circuit is just a device to add peak reading functionality to the meters basically.  It sounds like it is installed incorrectly or malfunctioning in such a way that a small amount of current is always going to the grid meter.

This is likely of only cosmetic concern, but worth checking in case the grid meter is no longer reading accurately at any level.

Worth asking Tom W8JI if there is a calibration pot in the TOF module to set 0 on the meter. 

In any circumstance, it is unlikely that it affects your amplifier's ability to make peak power.  As a triode amplifier, if you tune for maximum smoke and advance load a little, you will be linear and within AL-811 specifications.

In my personal opinion, the only real value of the TOF circuit is its ability to put the amp into standby if the grid current is exceeded (eg, antenna/feedline failure).  I do not put much stock in its ability to significantly increase linearity - anything it can do in that regard can be better done with proper station monitoring.  Heck, even an SDRPlay with a small random wire attached would provide better guidance in tuning for linearity.

I doubt I am the only one to have drawn these conclusions... I would personally find having a peak reading grid meter would be harmful and/or annoying.  Remember, grid current is roughly linear being higher with too much loading capacitance and lower with too little.  The sweet spot isn't obvious like it is with power, which in a simplistic sense follows a parabolic curve. 

Basically, simply knowing the peak grid current tells you absolutely nothing useful, other than the grid current is within design specifications.  Given that no other 811A design specifications are adhered to in the AL-811, and the grids are as tough as an incandescent bulb (eg, you WILL NOT fry them), the only advantage of the TOF circuit is it will save your plates if you have a sudden catastrophic antenna system failure.


On a side note, I was kinda trolling you Carl, but my point is, if you're going to criticize someone or their products, at least have the decency to state why.  As mentioned above, I am no fan of the TOF circuit, and have stated EXACTLY why.
« Last Edit: November 12, 2016, 04:56:57 PM by VK3BL » Logged

J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
VK3BL
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« Reply #12 on: November 12, 2016, 05:02:32 PM »

After installing W8JI TOF circuit in my AL-811 I now have a steady 10 mils of grid current showing when I power up the amp. This grid current stays steady at 10 mils even in standby. Current reads normal (approx. 150 mils) during operation.  Any ideas why this is and what affect it has on the amps ability to achieve full output?


Check that you haven't popped D16 the meter protection diode also.  It goes every time a tube farts, and it is a simple replacement being a 1N4007. 

I'd suggest you do this as 150ma of grid current does sound on the high side for a properly tuned AL-811.  Mine usually made full power between 70ma and 100ma with Russian/Chinese tubes, or 50ma and 80ma with RCAs.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
KB2OEV
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Posts: 7




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« Reply #13 on: November 13, 2016, 03:45:23 AM »

Thank you, I will check all these thins as soon as I have time and I'll report the results here.  I just got a new radio, so I now have to make up an interface cable to the amp because the one on the radio end is different.

Thanks,
Bob, KB2OEV
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W1QJ
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Posts: 2980




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« Reply #14 on: November 13, 2016, 05:45:50 AM »

After installing W8JI TOF circuit in my AL-811 I now have a steady 10 mils of grid current showing when I power up the amp. This grid current stays steady at 10 mils even in standby. Current reads normal (approx. 150 mils) during operation.  Any ideas why this is and what affect it has on the amps ability to achieve full output?


Check that you haven't popped D16 the meter protection diode also.  It goes every time a tube farts, and it is a simple replacement being a 1N4007. 

I'd suggest you do this as 150ma of grid current does sound on the high side for a properly tuned AL-811.  Mine usually made full power between 70ma and 100ma with Russian/Chinese tubes, or 50ma and 80ma with RCAs.


Of course D16 if shorted would show grid current indication at idle, but it is really not grid current at all.  When that diode shorts the grid meter is indicating plate current as it tracks the plate meter.  Sure, that is most likely the problem.  I should have thought of that.
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