>
>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
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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