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Author Topic: New Amp tuning question  (Read 3602 times)
AJ0Z
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« on: September 02, 2011, 12:07:25 PM »

Hi all, Another question on amplifier tuning if you don't mind. I finally have my AL-80B / ATR-30 up and running and all seems right with the world. I still can't get over busting pileups on a single cal or two when barefoot I was usually left out in the cold. A whole new world of Ham Radio, QRO!

My question is regarding power out from the amp. I tune the amp for max drive with max allowable input from the exciter with all currents kept in safe ranges. Now since I don't always need a full KW. Is the proper way to reduce power out from the amp just to reduce the exciter drive or to actually reduce output via the plate/ load controls. It seems I saw a thread saying the former over the later but I can't find it and I want to do it right to take the best care of my equipment.

As always thanks in advance for any and all comments.

Andy - AJ0Z
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K2DC
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« Reply #1 on: September 02, 2011, 01:27:32 PM »

Andy,

   Yes, the proper way to reduce output is to reduce the drive level, although you may need to touch up the tune and load controls a bit after you reduce the drive.  And it's my understanding that 3-500's like to be run at or near full output, so as long as your antennas system is stable (no sudden changes in VSWR) you're probably not adding much to tube life by running them lightly.  W8JI may chime in with more on that.

73,

Don, K2DC
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K9FV
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« Reply #2 on: September 03, 2011, 05:35:15 AM »

I'm no expert by any means, but I don't think you should "touch up" the plate or load after reducing drive.

Here is a GREAT page for tuning and the why's of what to do. http://www.w8ji.com/loading_amplifier.htm

"ALWAYS load your amplifier for maximum obtainable power, and reduce drive to rated, safe, or desired operating power levels"

Good luck and have fun,

73 de Ken H>
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AJ0Z
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« Reply #3 on: September 03, 2011, 09:50:18 AM »

Thanks Ken and Don for your replies. I thought I was on the right track but I will look into how the 3-500Z likes to be operated.
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AG6K
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« Reply #4 on: October 17, 2011, 06:45:51 PM »

Andy,

   Yes, the proper way to reduce output is to reduce the drive level, although you may need to touch up the tune and load controls a bit after you reduce the drive.  And it's my understanding that 3-500's like to be run at or near full output, so as long as your antennas system is stable (no sudden changes in VSWR) you're probably not adding much to tube life by running them lightly.  W8JI may chime in with more on that.

73,
Don, K2DC

  I autopsy 3-500Zs.  The most common failure I see are bent filament helices causing the filament to touch the grid when the filament is hot and expanded.  Rich, ag6k
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W1QJ
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« Reply #5 on: October 18, 2011, 05:08:39 AM »

Andy,

   Yes, the proper way to reduce output is to reduce the drive level, although you may need to touch up the tune and load controls a bit after you reduce the drive.  And it's my understanding that 3-500's like to be run at or near full output, so as long as your antennas system is stable (no sudden changes in VSWR) you're probably not adding much to tube life by running them lightly.  W8JI may chime in with more on that.

73,
Don, K2DC

  I autopsy 3-500Zs.  The most common failure I see are bent filament helices causing the filament to touch the grid when the filament is hot and expanded.  Rich, ag6k


Rich, What does your morbid forensic rant have to do with the loading up of a 3-500 based amplifier?
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W8JX
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« Reply #6 on: October 18, 2011, 06:42:33 AM »

And it's my understanding that 3-500's like to be run at or near full output

Yes, you do not baby a 3-500z. Unlike a 811 amp it is NORMAL for the anode(s) to glow dull red to red at times and not a cause for concern. If you baby it and not properly heat up anode it will not activate the gettering material on anode which absorb air molecules which normal leak in over time in a 3-500z.   When it starts glowing orange you are pushing it too hard.  Properly run a 3-500z can last many many years.
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W8JI
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« Reply #7 on: October 18, 2011, 07:13:23 AM »

 When it starts glowing orange you are pushing it too hard.  Properly run a 3-500z can last many many years.

Depends on the anode. Graphite uses a lower temperture gettering material and should not be made more than dull red.

The higher temperture molybdenum anode used by some manufacturers can be run bright orange at higher temperture areas without issues.

4-125A's run just about yellow hot at rated dissipation.
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AG6K
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« Reply #8 on: October 18, 2011, 07:18:12 AM »

 When it starts glowing orange you are pushing it too hard.  Properly run a 3-500z can last many many years.

Quote
Depends on the anode. Graphite uses a lower temperture gettering material and should not be made more than dull red

  what gettering material is that Mr. Rauch.  tnx
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W8JX
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« Reply #9 on: October 18, 2011, 07:36:39 AM »

 When it starts glowing orange you are pushing it too hard.  Properly run a 3-500z can last many many years.

Depends on the anode. Graphite uses a lower temperture gettering material and should not be made more than dull red.

The higher temperture molybdenum anode used by some manufacturers can be run bright orange at higher temperture areas without issues.

4-125A's run just about yellow hot at rated dissipation.

Well to reach "rated" dissipation of a 3-500z you are going to get more than dull red so there would not be much logic in using a low temp materiel for one is there? The point I was trying to make is no need to panic when you see anodes glowing some.
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W8JI
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« Reply #10 on: October 18, 2011, 08:41:19 AM »

Well to reach "rated" dissipation of a 3-500z you are going to get more than dull red so there would not be much logic in using a low temp materiel for one is there? The point I was trying to make is no need to panic when you see anodes glowing some.

Depends on the surface area of the anode. Most graphite anodes have considerably more surface area than moly anode tubes.
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AG6K
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« Reply #11 on: October 18, 2011, 02:47:16 PM »

Andy,

   Yes, the proper way to reduce output is to reduce the drive level, although you may need to touch up the tune and load controls a bit after you reduce the drive.  And it's my understanding that 3-500's like to be run at or near full output, so as long as your antennas system is stable (no sudden changes in VSWR) you're probably not adding much to tube life by running them lightly.  W8JI may chime in with more on that.

73,
Don, K2DC

  I autopsy 3-500Zs.  The most common failure I see are bent filament helices causing the filament to touch the grid when the filament is hot and expanded.  Rich, ag6k


Rich, What does your morbid forensic rant have to do with the loading up of a 3-500 based amplifier?

  Don == you're getting me mixed up with my cousin Virginia Ann since she autopsies dead humans and I autopsy dead tubes.

cheers
Rich, ag6k
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W8JX
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« Reply #12 on: October 18, 2011, 03:21:20 PM »

Well to reach "rated" dissipation of a 3-500z you are going to get more than dull red so there would not be much logic in using a low temp materiel for one is there? The point I was trying to make is no need to panic when you see anodes glowing some.

Depends on the surface area of the anode. Most graphite anodes have considerably more surface area than moly anode tubes.

Not from what I have seen. While they appear to have more thermal mass they cannot be formed in a multifaceted surface with a lot of surface like metal/moly can be. 
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N2EY
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« Reply #13 on: October 18, 2011, 03:35:47 PM »

Well to reach "rated" dissipation of a 3-500z you are going to get more than dull red so there would not be much logic in using a low temp materiel for one is there? The point I was trying to make is no need to panic when you see anodes glowing some.

Depends on the surface area of the anode. Most graphite anodes have considerably more surface area than moly anode tubes.

Not from what I have seen. While they appear to have more thermal mass they cannot be formed in a multifaceted surface with a lot of surface like metal/moly can be. 

The real issue is "what does the manufacturer data say?"

Tube data sheets, particularly RCA and Eimac, usually state what color the plate will be at various dissipation levels. In all cases I have seen, graphite anodes aren't supposed to show much if any color at maximum dissipation. OTOH, depending on the tube type and materials, metal anode color can range from none to bright orange in normal, within-ratings dissipation.

Just to make it more of a sporting course, the same basic tube type may be made differently over time and by different manufacturers. Most of the 813s I've seen were RCAs and had graphite plates, but I've seen at least one that had a metal plate (not sure if it was RCA). The 833 has a tantalum plate, the 833A has a zirconium-coated plate. Etc.

73 de Jim, N2EY

.....remembering the push-pull 450TLs at W3FDY, Field Day 1970, 40 ssb......
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W8JI
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« Reply #14 on: October 18, 2011, 04:11:59 PM »

The real issue is "what does the manufacturer data say?"

Which is based on dissipation and surface area to radiate heat.
Quote
Tube data sheets, particularly RCA and Eimac, usually state what color the plate will be at various dissipation levels. In all cases I have seen, graphite anodes aren't supposed to show much if any color at maximum dissipation. OTOH, depending on the tube type and materials, metal anode color can range from none to bright orange in normal, within-ratings dissipation.


Absolutely. Moly anodes can run hotter, and thus the anode can be physically much smaller in surface area, to radiate the same heat.

The 3-500Z is normally a brighter red color into slight yellow at rated dissipation.
The 3-500ZG is a very dull red at rated dissipation.

This is because the graphite has to be held at a lower temperature. To dissipate the same power, the graphite anode is manufactured with almost twice the effective emissive area for heat radiation. This allows a lower temperature delta  between the hot anode and the area around the tube.



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