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[Amps] AL-80B questions

To: "" <>
Subject: [Amps] AL-80B questions
From: "" <>
Date: Mon, 26 Jun 2006 11:44:48 -0400
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Hello Gentlemen,

I have a few questions about an Ameritron AL-80B amplifier that I converted for 
50 MHz mono-band service.

The first question goes to tuning the amplifier.  I am using a Vacuum Variable 
cap, 3 ? 30pF on the plate and the original air variable plate cap has been 
moved to the load position.  With 60 watts of drive, I achieve full amplifier 
output of approximately 900 watts with a grid current of 65ma and a plate 
current of 575ma.  This happens with the plate cap at minimum and the load cap 
at ½ its range or set in the ?middle?.  I can achieve the same output power 
results by ?screwing in? the plate cap and turning the load cap counter 
clockwise.  This setting yields a grid current of 100ma and a plate current of 
450ma.  The latter produces currents more typical of how it operated as an HF 

I do not have an O scope to check linearity.  That is on the list of items to 
purchase.  The first tuning method produces a more ?linear? gain reading up to 
800 watts output.  In other words, if I graph the input wattage against the 
output wattage, the resulting gain stays very close up to the 800 watt mark.  
The second tuning setting results in this gain measurement fluctuating up and 
down and drops of more at the 800 watt mark.  Any comments as to how this 
amplifier should be tuned?

The second question is that the internal watt meters show about a 100 watts 
more output (forward and reflected power) as compared to an external Bird 
wattmeter.  Can the internal watt meters be compensated for 50MHz to bring them 
closer to a true value?

The third question, when using the ALC, the power cuts back as expected in CW.  
However, when transmitting SSB, the ALC set point has to be set close to Zero 
to have an effect on the exciter?s drive power.  While transmitting on SSB, the 
grid current will only deflect about 20 or 30ma so the ALC never sees the 100ma 
that I had it set to cut back at.  Is this a typical issue on SSB?  

Lastly, while transmitting in SSB, the 3-500Z does not show any color.  I can 
transmit a long burst, 30 or 40 seconds, and never see a color change.  If I 
key the amp in CW, I can see light orange well before this time period.  Is it 
ok to operate in this manner and periodically operate CW to produce enough heat 
to ?condition? the tube?

Thanks for your input ? Doug N9XTF

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