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[AMPS] AL-1500 oscillation?

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Subject: [AMPS] AL-1500 oscillation?
From: (Rich Measures)
Date: Sun, 21 Feb 1999 03:35:40 -0800

>I noticed a problem with my Ameritron AL-1500 amp
>tonight.  When the amp is keyed in the CW position
>with no drive (but with the exciter connected to the
>input of the amp), all seems fine, with no RF out
>and no grid current.
>But if I then switch the mode position of the amp
>from CW to SSB, with no other changes, the grid current
>begins to flow (slowly at first, then more rapidly) 
>and the watt meter indicates about 50 W output.  

?  Is your AL-1500 allegedly "neutralized"?  
>If the feedline is removed from the exciter, the problem 
>persists.  However, if I then short the input, the grid
>current and power out drop to zero.  When the exciter is
>reconnected to the input, the amp takes off again.  This
>happens with the band switch in any position, but becomes
>progressively worse as you go lower in frequency.
>Since it's the weekend I haven't had an opportunity to
>contact Ameritron, but I'm wondering if others have 
>experienced this problem ...

?  yes.  Some owners have also experienced tube-failure due to 
gold-sputtering from the grid during intermittent oscillations.  

> and what was needed to correct it.
?   1.  Remove any  so-called "neutralization"  circuitry.  2.  Install 
glitch protection 
3. .Install a low vhf-Q parasitic-suppressor in the anode-circuit in 
order to reduce vhf voltage-gain.  .    
(note:  The AL-1500 is the only 8877 amp. ever manufactured on planet 
Earth that uses no vhf suppressor whatsoever) 

-  cheers, Arliss


R. L. Measures, 805-386-3734, AG6K,  

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