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Author Topic: using a Swan MK II on AM  (Read 1370 times)
W8JI
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« Reply #15 on: November 13, 2008, 10:10:47 PM »

The rule is on AM carrier the tubes have to dissipate about three times the carrier power. Tube dissipation is virtually always more of an issue than PEP power ratios or power supplies when dealing with AM linears.

375 watts carrier, which is 25% of 1500 watts, would be about 1125 watts anode dissipation.

There wasn't an old KW amateur amplifier manufactured that would handle that. They were designed when the plate input power was 1000 watts maximum any mode, and almost always for CW or SSB where efficiency was 50% or more and average power low. Even an amp that handles long RTTY or FM at 1 KW input would have a tough time on AM when tuned for good peak linerity.

When used on AM a class AB2 GG amp is lucky to do 25% carrier efficiency. That means the carrier heating in the tubes is about three times the carrier output power, and it is a long duty cycle. It really is a matter of how hot we want the tube seals to get, not the PEP power ratios or the power supply.

Of course it is possible to give up linearity and increase efficiency. That would work too.

73 Tom
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K9FON
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« Reply #16 on: November 14, 2008, 02:04:43 PM »

Well i have been running the4 amp at about 150 to 200 watts carrier on AM and i let it modulate to about 1 KW or so. My probem is the Icom 746 pretty much is worthless on AM.
W8JI, im sorry i was confused. I guess maybe i should get a BSEE in electronics engineering to be a ham to key up my radios! Oh well.
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W8JI
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« Reply #17 on: November 14, 2008, 04:55:14 PM »

Sorry if I offended you, but it is important to understand what the rules are with AM.

The dissipation in the tubes is generally about three times the carrier power on AM.

The PEP is four times the carrier power if everything is linear with 100% modulation.

From those numbers we find roughly the following:

200 watts carrier is 600 watts heat and 800 watts PEP.

300 watts carrier would be 900 watts heat and 1200 watts PEP

375 watts carrier would be 1500 watts PEP and and 1125 watts heat.

From that we can see heat in the tubes is the real issue unless the amp has a large amount of airflow and a pretty big tube. Most older KW amps barely handle 500 watts of heat without running the tubes over seal ratings. I can't think of any exceptions.

73 Tom

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N6AJR
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« Reply #18 on: November 17, 2008, 05:34:58 PM »

And remember, Tom is like one of the best on AMPS, period, and Steve is no slouch either. Ask tomm how many amplifiers he has designed over the years, and to list a few.. HI hi, I believe  both of them  over most others here on Eham..  They know their stuff.

tom N6AJR  ( the other tom)
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K9FON
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« Reply #19 on: November 18, 2008, 04:57:57 PM »

Well i bought an old Yaesu FT 101EE and it works well on am. I used it with the MK II tonight and it works well. Running about 200 watts carrier and modulates to about 1200 watts pep. I have not tried it on the air but it seems to run cool and so far no heat issues.
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