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Author Topic: new to amps  (Read 2285 times)
KC8Y
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Posts: 243




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« on: May 12, 2013, 05:53:49 AM »

I am new to amplifiers.  Plan on getting the AL-80B for my first introduction into using one; have I made a good chose Huh

Also, for the AL-80B operation (my xmtr is IC-7410), is/are any additional
devices I require for it to operate with my rig Huh

I've been licensed for over 40-years, BUT never used one before.  I'm 60 years old.

I only have a 120v circuit & only operate digital-modes
« Last Edit: May 12, 2013, 06:12:43 AM by KC8Y » Logged
N6AJR
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Posts: 9908




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« Reply #1 on: May 12, 2013, 12:57:00 PM »

that will be a great choice, see if there is a local ham who can tutor you on its operation, and you will need a cable with RCA jacks on both ends for the RLY connection.
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W8JX
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« Reply #2 on: May 12, 2013, 01:12:22 PM »

that will be a great choice, see if there is a local ham who can tutor you on its operation, and you will need a cable with RCA jacks on both ends for the RLY connection.


Yes good choice. Digital is a high duty cycle mode so limit output to about 600 watts.
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AD9DX
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Posts: 1480




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« Reply #3 on: May 13, 2013, 09:01:31 AM »

I can't think of a better starter amp. The tube is rugged and still plentiful. The power supply is far beefier than the AL-811 and you have a bit more margin with getting the hang of tuning.

And the advice about keeping the drive at or below 600w is spot on. Go ahead and get a watt meter to monitor output and SWR and the amp should last you a long time. 
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WX7G
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« Reply #4 on: May 14, 2013, 11:03:39 AM »

Be sure to tune the amp at 600 watts. That means to tune for maximum power using the TUNE and LOAD controls while keeping the driver power such that 600 watts is achieved. This will result in maximum efficiency (about 60%) with the tube plate dissipating 400 watts.

If tuned at 1 kW, then backed down to 600 watts by reducing the drive, the efficiency will be about 36% and the tube plate dissipation will be about 1000 watts.

The color of the tube plate will tell the story. Anything hotter than orange is too hot.
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K4RVN
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Posts: 770




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« Reply #5 on: May 14, 2013, 11:15:09 AM »

Dave, I am glad to see that you clarified maximum amp power in your post. So many newbies read posts by others and think one has to use maximum drive to tune and that is not the case as you know.
Once the drive is set say to 50 watts, then you need to tune for max power out at 50 watts drive to get the efficiency you mentioned. Also It is my perception that many tube failures are the result of improper tuning with max drive by inexperienced operators. If I am wrong in my thinking I'm sure someone will call my hand.

Frank
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W8JX
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« Reply #6 on: May 14, 2013, 11:22:08 AM »

It is my perception that many tube failures are the result of improper tuning with max drive by inexperienced operators. If I am wrong in my thinking I'm sure someone will call my hand.

Could not agree more. Many run max power into amp. I run same power barefoot and with amp. 50 watts. 
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W6UV
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Posts: 538




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« Reply #7 on: May 14, 2013, 12:26:49 PM »

Also It is my perception that many tube failures are the result of improper tuning with max drive by inexperienced operators.

I see this mentioned all the time. As a new amp user myself, I'm wondering what "improper tuning" is -- can someone explain it?

Does it mean trying to tune up on 20M with the amp's band switch set to 80M? Or perhaps having the tune and load controls not set to approximate values before starting to tune? Or maybe tuning up for several minutes at a time (I sure hear a lot of this on the bands, which puzzles me because I can tune my manual-tune amp in about 5 seconds max).

I'd really like to know what improper tuning is so I can avoid it.
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K4RVN
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« Reply #8 on: May 14, 2013, 01:11:59 PM »

Hello W6uv,
If you can tune in 5 seconds, you have nothing to worry about. Improper tuning in my view includes all you mentioned plus trying to get the meters to read the manual tuning values when on SSB.
Also not having a device to read watts at the output of the amp; switching bands while the amp is in the operate position. I am not condemning these inexperienced ops, just identifying their mistakes which could help them in the long run. All you have to do is read the amp forum often to see how confused some are. This also includes long time ops with no amp use experience.
You  could also include too much drive when adding drive does no increase power out from the amp as well as prolonged tuning exceeding the max currents.
I think I did all of the above when I first bought an amp.

Frank
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WB2WIK
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Posts: 20595




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« Reply #9 on: May 17, 2013, 10:48:06 AM »

Also It is my perception that many tube failures are the result of improper tuning with max drive by inexperienced operators.

I see this mentioned all the time. As a new amp user myself, I'm wondering what "improper tuning" is -- can someone explain it?

Does it mean trying to tune up on 20M with the amp's band switch set to 80M? Or perhaps having the tune and load controls not set to approximate values before starting to tune? Or maybe tuning up for several minutes at a time (I sure hear a lot of this on the bands, which puzzles me because I can tune my manual-tune amp in about 5 seconds max).

I'd really like to know what improper tuning is so I can avoid it.

Biggest mistake I see is peaking PLATE and LOAD for maximum output power and then just leaving it like that.  With most amps, this is an underloaded condition and more LOADing will improve linearity.

With the AL-80B (and lots of other manually tuned tube amplifiers), I tune for max output then while observing grid current, I increase loading some more to reduce the Ig about 10%.  THEN, it's loaded.  IMD measurements confirm heavy loading produces cleaner signals, almost always.

UNDERloaded amps not only generate higher IMD, but often needlessly bang the grids when it's just not necessary.
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W6UV
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Posts: 538




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« Reply #10 on: May 18, 2013, 08:00:08 AM »

Also It is my perception that many tube failures are the result of improper tuning with max drive by inexperienced operators.

I see this mentioned all the time. As a new amp user myself, I'm wondering what "improper tuning" is -- can someone explain it?

Does it mean trying to tune up on 20M with the amp's band switch set to 80M? Or perhaps having the tune and load controls not set to approximate values before starting to tune? Or maybe tuning up for several minutes at a time (I sure hear a lot of this on the bands, which puzzles me because I can tune my manual-tune amp in about 5 seconds max).

I'd really like to know what improper tuning is so I can avoid it.

Biggest mistake I see is peaking PLATE and LOAD for maximum output power and then just leaving it like that.  With most amps, this is an underloaded condition and more LOADing will improve linearity.

With the AL-80B (and lots of other manually tuned tube amplifiers), I tune for max output then while observing grid current, I increase loading some more to reduce the Ig about 10%.  THEN, it's loaded.  IMD measurements confirm heavy loading produces cleaner signals, almost always.

UNDERloaded amps not only generate higher IMD, but often needlessly bang the grids when it's just not necessary.

How would you do this on a tetrode amp where there's no grid current to speak of?
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