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[AMPS] [Fwd: AL-1500 oscillation]

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Subject: [AMPS] [Fwd: AL-1500 oscillation]
From: (W7XU Arliss)
Date: Tue, 23 Feb 1999 17:50:42 +0000
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It seems likely that the cause of the oscillation in
my AL-1500 is identified (see the note below).  Now to
have my QSK board modified and see if that cures the

Thanks to all for the suggestions.

73,  Arliss  W7XU
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To: <>
Date: Mon, 22 Feb 1999 19:06:14 -0500
From: Tom Rauch <>
Subject: Re: AL-1500 oscillation
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Date sent:              Mon, 22 Feb 1999 22:48:06 +0000
From:                   W7XU Arliss <>
Subject:                Re: AL-1500 oscillation
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Organization:           personal

> Hi Tom,
> You are correct, I have a QSK board in the amp (sorry I 
> forgot to mention that in the original note).  So now
> I have some hope that there is a cure in sight.  Great!

You might post the cause back to the amps reflector. Once again 
the oscillation is a VLF parasitic (this is also seen in some SB-
220's but for a different reason). I might have explained the problem 
incorrectly in my last e-mail.

The cause in the AL-1500 is the dc path for the diode control 
voltages is decoupled by series chokes and shunt capacitors, that 
form a low pass filter. Since the input and output circuits are also 
low pass filters the low pass filter formed by the components in the 
QSK board can, under certain load conditions and component 
tolerances, provide enough low frequency feedback to make the 
amp oscillate.

The safest solution is to pull the board and return it to Ameritron. 
They will make the mods and return the board to you at no charge.

73, Tom W8JI


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