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Re: [Amps] How to tune an FL-2100B

To: <amps@contesting.com>, "Dan Wright" <dwright12@neb.rr.com>
Subject: Re: [Amps] How to tune an FL-2100B
From: "Tom W8JI" <w8ji@w8ji.com>
Date: Tue, 4 Jul 2006 10:39:57 -0400
List-post: <mailto:amps@contesting.com>
>>PEP from the FT101EX could be as much as 150 watts. That 
>>means the FL2100 needs to be fully loaded at 150 watts of 
>>CW carrier drive, and that is just too much.  You'd need 
>>an attenuator pad between the amp and rig or really watch 
>>your control settings.
>
> Why can't I just reduce the drive on the '101 to 25 watts 
> and drive the amp with that?

25 watts carrier? That's 100 watts PEP if you watch the peak 
envelope power and use the controls properly to maintain 
that peak level.
You'd need a good PEP reading meter. The Ameritron PEP meter 
is a very good one for this application since it even reads 
extremely short peaks accurately and holds the level on the 
meter, and it also reads pretty close on avarage power. The 
key will be a good meter.

> From brief experience:
>
> It looks like if I drive the amp with 25 watts, I get 
> around 125 -130 watts out of the
> amp. Four times that (PEP) is 520 watts, well below the 
> 1200 watts PEP rating
> of the amp.

Well, in order to be LINEAR amplifier carrier efficiency has 
to be about half or less the efficiency on full power peaks. 
Let's assume the 2100 makes 60% efficiency at full drive. 
That means 30% or less efficiency on carrier, so we'll guess 
25% to be safe.

At 25% carrier efficiency four times the power would be the 
input power, or 130 watts times four or 520 watts. That 
means the anode heat is 520-130 or 390 watts. The tubes are 
rated at 160 watts each, so you are 35 watts over each 
tube's dissipation limit.

If you are NOT over each tube's dissipation limit at 130 
watts carrier, the amplifier is almost certainly mistuned 
for linear AM service.

Now if you wanted to run the 572's at 2/3 of rated 
dissipation on AM,  you have 320*.666 = 213 watts 
dissipation available. With 213 watts dissipation you have 
284 watts input available, 213 watts of heat, and 71 watts 
of carrier.

Now you don't have to run the amp that way, but that's 
probably a reasonable value for AM. The tubes won't melt and 
it would be linear. You also would not have high voltages on 
the tank circuit on audio peaks.

Linear amplifiers on AM are generally heat limited, not peak 
power limited, when properly tuned.

73 Tom 


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